Biomedical subjects

R L Moss

Publications and source records attributed to R L Moss.

At least 109 records · Page 6Linked to original sources

PubMed1995

Calcium sensitivity of isometric tension is increased in canine experimental heart failure.

To examine the role of alterations in myofibrillar function in chronic heart failure, we determined isometric tension-pCa relations in permeabilized myocardium from a canine model of dilated cardiomyopathy (DCM) produced by chronic rapid pacing. In the initial series of experiments, seven dogs were paced at 250 beats per minute for 28.9 +/- 7.0 days, resulting in ventricular dilatation and reduced ejection fractions by echocardiography and elevated intracardiac filling pressures. Isometric tension-pCa relations were measured by using mechanically disrupted and permeabilized myocyte-sized preparations obtained from left ventricular biopsies before (n = 11) and after (n = 10) chronic rapid pacing-induced heart failure. Resting sarcomere length (SL) was set at 2.35 microns, and preparations had low end compliance (SL was 2.23 +/- 0.03 microns during maximal activation). Passive tension (2.1 +/- 1.0 versus 2.4 +/- 0.6 mN/mm2) and maximal Ca(2+)-activated tension (25.9 +/- 9.3 versus 27.8 +/- 6.8 mN/mm2) were similar for control and DCM preparations, respectively. However, the calcium sensitivity of isometric tension was increased in failing myocardium (pCa50 5.95 +/- 0.11 [DCM] versus 5.83 +/- 0.10 [control], P = .001). Treatment of myofibrillar preparations with the catalytic subunit of protein kinase A decreased calcium sensitivity of tension to a greater degree in failing preparations (shift of pCa50 from 6.04 +/- 0.06 to 5.75 +/- 0.09, n = 7) than in nonfailing preparations (5.91 +/- 0.08 to 5.74 +/- 0.07, n = 8), and isometric tension-pCa relations in the two groups were not significantly different after protein kinase A treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Agonists↗

PubMed1995

Alpha 1-adrenergic receptor stimulation decreases maximum shortening velocity of skinned single ventricular myocytes from rats.

alpha 1-Adrenergic agonists have negative inotropic effects on mammalian myocardium under some conditions, and biochemical experiments measuring the Ca(2+)-activated actomyosin ATPase activity of myofibrillar preparations suggest that this may result from a decrease in cross-bridge cycling rate caused by phosphorylation of myofilament proteins. Experiments with intact ventricular preparations, however, have failed to demonstrate a mechanical manifestation of a decrease in cycling rate. The present study examined the effect of alpha 1-adrenergic receptor stimulation on maximum shortening velocity in skinned single ventricular myocytes from rats. Enzymatically isolated myocytes were incubated with the beta-receptor antagonist propranolol in the presence or absence of the alpha 1-adrenergic receptor agonist phenylephrine and were then rapidly skinned to preserve the phosphorylation state of myofilament proteins. The velocity of unloaded shortening (Vo) was determined by use of the slack-test method and compared between skinned control and phenylephrine-treated cells. The relationship between isometric tension and [Ca2+] was also assessed for each myocyte. Vo was significantly lower in the alpha 1-adrenergic receptor agonist-treated cells than in the control cells, but there was no effect on Ca2+ sensitivity of isometric tension. In addition, the myosin heavy chain isoform composition accounted for a significant amount of the variation in Vo within the treatment groups. On the basis of these and previous results we propose that alpha 1-adrenergic receptor stimulation inhibits cross-bridge cycling rate at the level of myofilament proteins by a mechanism that may involve phosphorylation of troponin I by protein kinase C.

Actin Cytoskeleton↗

PubMed1995

Osmotic compression of single cardiac myocytes eliminates the reduction in Ca2+ sensitivity of tension at short sarcomere length.

According to the Frank-Starling relation, cardiac output varies as a function of end-diastolic volume of the ventricle. The cellular basis of the relation is thought to involve length-dependent variations in Ca2+ sensitivity of tension; ie, as sarcomere length is increased in cardiac muscle, Ca2+ sensitivity of tension also increases. One possible explanation for this effect is that the decrease in myocyte diameter as muscle length is increased reduces the lateral spacing between thick and thin filaments, thereby increasing the likelihood of cross-bridge interaction with actin. To examine this idea, we measured the effects of osmotic compression of single skinned cardiac myocytes on Ca2+ sensitivity of tension. Single myocytes from rat enzymatically digested ventricles were attached to a force transducer and piezoelectric translator, and tension-pCa relations were subsequently characterized at short sarcomere length (SL), at the same short SL in the presence of 2.5% dextran, and at long SL. The pCa (-log[Ca2+]) for half-maximal tension (ie, pCa50) increased from 5.54 +/- 0.09 to 5.65 +/- 0.10 (n = 7, mean +/- SD, P < .001) as SL was increased from approximately 1.85 to approximately 2.25 microns. Osmotic compression of myocytes at short length also increased Ca2+ sensitivity of tension, shifting tension-pCa relations to [Ca2+] levels similar to those observed at long length (pCa50, 5.68 +/- 0.11). These results support the idea that the length dependence of Ca2+ sensitivity of tension in cardiac muscle arises in large part from the changes in interfilament lattice spacing that accompany changes in SL.

Analysis of Variance↗

PubMed1995

Cardiac sarcoplasmic reticulum phosphorylation increases Ca2+ release induced by flash photolysis of nitr-5.

Effects on Ca(2+)-induced Ca2+ release due to phosphorylation of sarcoplasmic reticulum (SR) proteins were investigated in isoproterenol-treated saponin-permeabilized trabeculae from rat ventricles. In these experiments, Ca2+ release from the SR was induced by a rapid change in concentration of free Ca2+ (ie, trigger Ca2+) achieved by flash photolysis of nitr-5, and the amount of Ca2+ released was assessed by measuring isometric tension. Ca2+ uptake by the SR was more rapid, and the amount of Ca2+ released by a given concentration of trigger Ca2+ was greater in isoproterenol-treated trabeculae compared with control trabeculae. However, under the same conditions of Ca2+ loading, the amplitudes of caffeine-elicited tension transients in control trabeculae were similar to those in isoproterenol-treated trabeculae, suggesting that the Ca2+ available for release was similar in the two cases. Control experiments showed that there were no significant differences in Ca2+ sensitivity of tension between isoproterenol-treated and control trabeculae. Also, application of alkaline phosphatase to trabeculae that had previously been treated with isoproterenol returned SR Ca2+ release to control levels. We conclude that the greater release of Ca2+ in isoproterenol-treated trabeculae in response to a given concentration of trigger Ca2+ is due to phosphorylation of SR proteins, most likely the Ca2+ release channel.

Alkaline Phosphatase↗

PubMed1995

Isometric and dynamic contractile properties of porcine skinned cardiac myocytes after stunning.

The purpose of this study was to investigate myofibrillar mechanisms of depressed contractile function associated with myocardial stunning. We first tested whether the degree of stunning was directly related to changes in myofilament Ca2+ sensitivity. Variable degrees and durations of low-flow ischemia were followed by 30 minutes of reperfusion in an open-chest porcine model of regional myocardial stunning (n = 27). Ca2+ sensitivity of isometric tension was measured in skinned myocytes obtained from endocardial biopsies taken during control aerobic flow and after 30 minutes of reperfusion. The degree of stunning, as assessed by percent systolic wall thickening, ranged from -3% to 75% of control but did not correlate (r = .11) with changes in pCa50, ie, pCa for half-maximal tension. Only in the group (n = 10) with the most severe level of ischemia was there a significant decrease in pCa50 (from 5.97 +/- 0.06 in the control condition to 5.86 +/- 0.07 after ischemia, P < .05). Less severe levels of ischemia (n = 17) resulted in significant stunning (percent systolic wall thickening, 38 +/- 4% of control) but no change in pCa50. To investigate the possibility that alterations in myofibrillar cross-bridge kinetics contribute to depressed function in stunning, maximum velocity of shortening (Vo) was measured in postischemic myocytes. Vo in postischemic myocytes was reduced to 56 +/- 4% of Vo in control myocytes and was independent both of the degree of stunning (r = .26) and changes in Ca2+ sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1994

Lesions of the accessory olfactory bulb decrease lordotic responsiveness and reduce mating-induced c-fos expression in the accessory olfactory system.

The effect of bilateral lesion of the accessory olfactory bulb (AOB) on the mating-induced enhancement of sexual receptivity was investigated in ovariectomized (OVX) female rats. Lesions of the AOB significantly reduced the lordosis-to-mount (L/M) ratio in mating tests conducted 20 to 50 days after the lesion but L/M ratios at earlier (10 days) and later (51-90 days) time periods were not affected. The decrease in L/M was accompanied by a reduction in the number of c-fos immunopositive cells in the medial amygdala (mAMYG) and bed nucleus of the stria terminalis (BNST) measured after 3 h of repetitive mating. In the mAMYG, the reduction in c-fos immunoreactivity was correlated to the L/M ratio as well as to the number of intromissions received during the mating tests. The results suggest that information processed from the AOB to the mAMYG and the BNST is important for facilitation of lordosis behavior, and that the mAMYG may integrate information from the AOB with ascending input activated during copulatory behavior to regulate receptivity.

Amygdala↗

PubMed1994

Vomeronasal organ-mediated induction of fos in the central accessory olfactory pathways in repetitively mated female rats.

Removal of the VNO significantly reduced the enhancement of lordosis and the induction of fos immunoreactivity in luteinizing hormone-releasing hormone (LHRH) neurons in ovariectomized estrogen-primed rats. There was a significant positive correlation between the two variables. In the accessory olfactory bulb (AOB) of the repetitively mated rats, the number of fos-positive cells in the granule (G) cell layer was significantly lower in the VNO-removed rats, whereas that in the mitral (M) cell layer was not significantly different between VNO-removed and VNO-sham females. The G/M ratio (calculated by dividing the mean number of fos-positive cells in the G cell layer by that in the M cell layer), taken as an estimate of the output of the AOB, was relatively larger in the VN-sham as compared with the VNO-removed rats. There were significant positive correlations between G/M ratio and the increase in LQ and between the G/M ratio and the percentage of fos-positive LHRH cells. The positive correlation between the number of fos-positive cells in the posterodorsal medial amygdala (PDMA) and the increase in LQ and that between the number of fos-positive cells in the PDMA and the percentage of fos-positive LHRH cells were significant, supporting the role of the medial nucleus of amygdala in lordosis. However, the correlation between G/M ratio and the number of fos-positive cells in the PDMA was not significant, indicating that fos immunoreactivity in the PDMA is not directly related to that in the AOB.(ABSTRACT TRUNCATED AT 250 WORDS)

Amygdala↗

PubMed1994

Estrogen regulation of dopamine release in the nucleus accumbens: genomic- and nongenomic-mediated effects.

The ability of estrogen to modulate mesolimbic dopamine (DA) was examined using in vivo voltammetry. Estrogen priming (5 micrograms, 48 h) of ovariectomized (ovx) female rats resulted in a slight decrease in K(+)-stimulated DA release measured in the nucleus accumbens: this decrease was accompanied by a significant increase in both DA reuptake and DA clearance times. Following estrogen priming nomifensine, a potent inhibitor of the DA uptake carrier, was still able to potentiate K(+)-stimulated DA release and alter the time course of DA availability, but the response was attenuated compared with ovx controls. Direct infusion of 17 beta-estradiol hemisuccinate (17 beta-E, 20-50 pg) into the nucleus accumbens resulted in a biphasic potentiation of K(+)-stimulated release. An initial increase in release was observed 2 min after 17 beta-E infusion; this increase, although reduced by 15 min, was still significantly higher than control values. A subsequent potentiation was observed 60 min after the initial 17 beta-E infusion; this response remained for at least an additional 60 min. Nomifensine did not significantly alter K(+)-stimulated DA release following 17 beta-E infusion, but was still able to potentiate the total time DA was available extracellularly. These data suggest that the mesolimbic A10 DA neurons that terminate in the nucleus accumbens can be modulated in vivo by estrogen and that this modulation may be mediated by both genomic (long term) and nongenomic (short term) mechanisms.

Analysis of Variance↗

PubMed1994

Patch-clamp analysis of direct steroidal modulation of glutamate receptor-channels.

Steroid hormones regulate the neuroendocrine and behavioral functions of the brain by using a number of diverse cellular mechanisms. Many steroids exert rapid electrophysiological effects on neurons, involving specific interactions with membrane components, such as neurotransmitter receptors. Previous studies suggest that the steroids, estrogen and pregnenolone sulfate (PS), might directly modulate glutamate receptors. The present experiments utilized patch-clamp recording of glutamate receptor-channels in excised membrane patches to test for direct modulation by these steroids. Characteristic single-channel activity from N-methyl-D-aspartate (NMDA) receptors could be elicited in both inside-out and outside-out patches excised from acutely dissociated hippocampal neurons. PS, but not 17 beta-estradiol, increased the open probability of NMDA channel activity in inside-out and outside-out patches. The PS-induced increase in open probability could be attributed to an increase in both frequency of opening and mean open time of the NMDA receptor, though the effect on frequency of opening was more prominent. The non-NMDA agonist, kainate, induced continuous shifts and increased noise in the baseline current of outside-out patches, but rarely activated clearly resolvable single-channel openings. 17 beta-estradiol and PS had no apparent effect on the kainate-induced currents. These findings suggest that some steroids can directly modulate glutamate receptors, but other steroids may utilize indirect mechanisms for regulating glutamatergic synaptic transmission.

Animals↗

PubMed1994

Beta-adrenergic receptor stimulation increases unloaded shortening velocity of skinned single ventricular myocytes from rats.

In vitro biochemical experiments have suggested that stimulation of beta-adrenergic receptor may increase the rate of crossbridge cycling in mammalian myocardium, but recent attempts to demonstrate a mechanical correlate have yielded conflicting results. To investigate this issue, we measured the effect of isoproterenol (ISO) and cAMP-dependent protein kinase (PKA) on unloaded shortening velocity (Vo). Vo is thought to be determined by the rate-limiting step of the crossbridge cycle, ie, the rate of crossbridge detachment from actin, and is therefore an index of the cycling rate. Single rat ventricular myocytes were enzymatically isolated, incubated in Ringer's solution without (control) or with 0.1 mumol/L ISO, and then rapidly skinned. Some control cells were subsequently treated with 3 micrograms/mL PKA for 40 minutes. Vo was then measured during maximal activation (pCa 4.5) in control, ISO-treated, and PKA-treated cells using the slack-test method. To test the efficacy of the agonist treatments, Ca2+ sensitivity of isometric tension was also assessed for each treatment by determining the [Ca2+] required for half-maximal tension (ie, pCa50). Both ISO and PKA treatment reduced the Ca2+ sensitivity of isometric tension compared with same-day control cells, in agreement with previous studies in intact and in skinned preparations. Vo was increased 38% by ISO treatment and 41% by PKA treatment compared with same-day control cells. 32P autoradiography showed that troponin I and C protein were the principal proteins phosphorylated by PKA treatment. We conclude that beta-adrenergic stimulation increases the rate of crossbridge release from actin, by a mechanism that most likely involves the phosphorylation of troponin I and/or C protein by PKA.

Animals↗

PubMed1993

Gap junction communication modulates [Ca2+]i oscillations and enzyme secretion in pancreatic acini.

Global (all cells in an acinus) and focal (1-2 out of 10-15 cells) stimulation of pancreatic acini with bombesin or t-butyloxycarbonyl-Tyr(SO3)-Nle-Gly-Tyr-Asp-2-phenylethyl ester (CCKJ) together with modulation of gap junction (GJ) permeability by octanol and NO2- was used to study the role of GJ permeability in controlling [Ca2+]i oscillations and enzyme secretion. GJ permeability was quantitated by measuring fluorescence recovery after photobleaching. Octanol at 0.5 mM markedly reduced, whereas 15 mM NO2- increased GJ permeability. Focal application of bombesin caused synchronized oscillations in the entire acinus, whereas global stimulation resulted in asynchronous oscillations. Increasing GJ permeability with NO2- had no effect on bombesin-evoked [Ca2+]i oscillations. Octanol inhibited ongoing oscillations evoked by focal or global bombesin stimulation. However, when GJ were blocked prior to stimulation, subsequent global stimulation with bombesin induced long-lasting oscillations in all cells. Re-establishing GJ communication for as little as 37.5 s conferred GJ dependence on the order and time of [Ca2+]i spiking evoked by global bombesin stimulation. Focal and global stimulation with CCKJ gave different patterns of [Ca2+]i oscillations. However, in contrast to bombesin, inhibition of GJ with octanol had no effect on oscillations induced by global CCKJ stimulation. Increasing GJ permeability with NO2- synchronized CCKJ-stimulated oscillations by equalizing the amplitude and increasing the frequency in all cells within an acinus. These observations suggest that amplitude and frequency of [Ca2+]i oscillations can be regulated independently of each other, and that GJ permeable molecules modulate the frequency of [Ca2]i oscillation in an agonist-specific manner. Regardless of the agonist, increasing the frequency of oscillations by modulation of GJ permeability correlated with an increased enzyme secretion.

Animals↗

PubMed1993

The role of the medial nucleus of amygdala in the mating-induced enhancement of lordosis in female rats: the interaction with luteinizing hormone-releasing hormone neuronal system.

The effect of bilateral lesion of the medial nucleus of amygdala (mAMY) on the mating-induced enhancement of lordosis behavior in ovariectomized (OVX) estrogen-primed rats was investigated. The enhancement of lordosis following repeated coital stimulation was significantly reduced in the mAMY-lesioned rats as compared with the sham-operated controls. Double labeling immunocytochemistry of the brain of the repeatedly mated females for Fos protein and luteinizing hormone-releasing hormone (LHRH) revealed that a significantly lower percentage of the LHRH neurons in the mAMY-lesioned females exhibited Fos immunoreactivity than the controls. This suggests that bilateral destruction of the mAMY suppresses the activation of the LHRH neuronal system following repeated mating. Furthermore, the correlation between the number of Fos-positive LHRH neurons and lordosis-to-mount ratio in the sham-females was significant, while a similar comparison in mAMY-lesioned females was not significant. Since LHRH is reported to enhance lordosis behavior in OVX estrogen-primed rats, it appears likely that the effects of mAMY on lordosis are mediated through the LHRH neuronal system. The results further support the involvement of the accessory olfactory system in the mating-induced enhancement of lordosis behavior in female rats.

Amygdala↗

PubMed1993

Hepatobiliary dysfunction during total parenteral nutrition is caused by infusate, not the route of administration.

Cholestatic jaundice is the major complication of total parenteral nutrition (TPN). Both the intravenous (IV) route of nutrition and the enteral fast have been implicated as causes of TPN-associated cholestasis (TPN-AC). The purpose of this study was to determine whether TPN-AC is caused by the TPN solution itself or the IV route of administration and enteral fast. Prepubescent rabbits (n = 24) were divided into four groups: CONTROL, fed standard lab chow; TPN, received a standard hyperalimentation solution of dextrose, Aminosyn, and lipids via the jugular vein; ENT, received the same hyperalimentation solution via a duodenostomy tube; and OSM, received a polymeric formula (Osmolite) via a duodenostomy tube. After 14 days on these diets, we measured bile flow, bile acid excretion, sulfobromophthalein (BSP) excretion, plasma amino acid profile, serum liver enzymes, and liver histology. Statistical analysis was by analysis of variance. Hyperalimentation solution significantly depressed hepatobiliary function, whether it was given IV or by gut. Bile flow in both the TPN (36.4 microL/kg/min) and ENT (46.2) groups was significantly less than CONTROL (84.5) or OSM (62.9). Hepatic secretory function, measured by excretion of the cholephilic dye BSP, was depressed in both TPN and ENT (57% and 55% of IV dose excreted in bile over 60 minutes, respectively) compared with CONTROL (84%) or OSM (71%). Serum liver enzymes were normal in all groups. Histological injury similar to TPN-AC in humans (portal inflammation and hepatocyte degeneration) was seen in both groups receiving the hyperalimentation solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1993

Excitatory and inhibitory synaptic processing in the accessory olfactory system of the female rat.

The accessory olfactory system constitutes a sensory system specifically involved in regulating neuroendocrine function and reproductive behavior. The chemosensitive structure of this system, the vomeronasal organ, exclusively innervates the accessory olfactory bulb, which in turn projects via mono- or disynaptic pathways to a limited number of regions implicated in endocrine and sexual function, including the amygdala and hypothalamus. The present study investigated synaptic processing between the different levels of this sensory system, with particular focus on the input from the accessory olfactory bulb to the medial amygdala and the reciprocal connections between the medial amygdala and the ventromedial hypothalamus. Extracellular single-unit recordings were obtained from medial amygdala neurons in anesthetized female rats to study the synaptic responses elicited by stimulation of the olfactory bulb and hypothalamus. Locally applied agonists and antagonists of amino acid neurotransmitters were tested for their ability to mimic and block these synaptic responses in an attempt to identify the neurotransmitters involved in the stimulated pathways. Electrical stimulation of the accessory olfactory bulb induced orthodromic responses in 88% of 288 medial amygdala neurons, with 67% showing orthodromic inhibition and 21% showing excitation as the shortest-latency response. Many cells displayed multiphasic responses with both orthodromic excitation and inhibition. In separate experiments, main olfactory bulb stimulation also produced excitatory (39%) or inhibitory (50%) orthodromic responses in medial amygdala neurons (n = 105), but the latency and distribution of responses were significantly different than with accessory olfactory bulb stimulation. Stimulation of the ventromedial hypothalamus also had prominent excitatory (29%) or inhibitory (59%) orthodromic actions on the majority of amygdala neurons. Out of 288 cells tested with both accessory olfactory bulb and ventromedial hypothalamus stimulation, 79% were orthodromically responsive to both areas, whereas only 3% responded to neither area. Fourteen (6%) medial amygdala neurons were antidromically activated from the ventromedial hypothalamus, and 11 of these 14 cells were simultaneously orthodromically responsive to accessory olfactory bulb stimulation, indicating that the accessory olfactory bulb can influence medial amygdala neurons that project directly to the hypothalamus. Iontophoretic application of drugs to the medial amygdala revealed that glutamate and GABA consistently mimicked the orthodromic excitatory and inhibitory responses, respectively, from both the accessory olfactory bulb and ventromedial hypothalamus. In some cases, ejection of bicuculline could block or reverse excitation of the orthodromic inhibitory responses, whereas kynurenic acid could eliminate the orthodromic excitation, indicating that excitatory and inhibitory amino acid transmitters are at least partially involved in these pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗

PubMed1993

Total parenteral nutrition-associated cholestasis: clinical and histopathologic correlation.

Cholestatic jaundice is the major complication of total parenteral nutrition (TPN) in infants and children. The pathogenesis of this syndrome is poorly understood. The aims of this study were: (1) to define the histologic liver injury in relation to the clinical course of infants on TPN and (2) to determine whether enteral feeding will reverse or halt these changes. We identified 31 infants treated for severe gastrointestinal disease for whom liver histology was available from 1987 to 1991. Clinical records and liver biopsy (23) or autopsy specimens (13) were reviewed. Five patients had biopsies at two subsequent operations. The clinical diagnosis was necrotizing enterocolitis (24), atresia or stenosis (3), midgut volvulus (2), Hirschsprung's disease (1), and sepsis (1). Twenty-one of 31 infants were premature and had a mean birth weight of 1,868 g. Twenty-five of 31 were on TPN and 28 of 31 had received some enteral feeding by the time of the biopsy. Enteral feeding was begun as early as possible in all infants even if continued TPN was necessary for full support. Cholestasis occurred in 71% of premature infants versus 22% of full-term babies. Infants with cholestasis had been on TPN for a longer time (37 days v 18) with a correspondingly shorter period of enteral feeding (17 days v 27). Mean total bilirubin level was 14 in patients with cholestasis and 5 in those without, but the bilirubin level did not correlate with the extent of histological injury and was frequently normal despite marked histological damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile Ducts, Intrahepatic↗

PubMed1993

Tension transients initiated by photogeneration of MgADP in skinned skeletal muscle fibers.

Addition of MgADP to skinned skeletal muscle fibers causes a rise in Ca(2+)-activated isometric tension. Mechanisms underlying this tension increase have been investigated by rapid photogeneration of ADP within skinned single fibers of rabbit psoas muscle. Photolysis of caged ADP (P2-1(2-nitrophenyl)ethyladenosine 5'-diphosphate) resulted in an exponential increase in isometric tension with an apparent rate constant, kADP, of 9.6 +/- 0.3 s-1 (mean +/- SE, n = 28) and an amplitude, PADP, of 4.9 +/- 0.3% Po under standard conditions (0.5 mM photoreleased MgADP, 4 mM MgATP, pH 7.0, pCa 4.5, 0.18 M ionic strength, 15 degrees C). PADP depended upon the concentration of photoreleased MgADP as well as the concentration of MgATP. A plot of 1/PADP vs. 1/[MgADP] at three MgATP concentrations was consistent with competition between MgADP and MgATP for the same site on the crossbridge. The rate of the transient, kADP, also depended upon the concentration of MgADP and MgATP. At both 4 and 1 mM MgATP, kADP was not significantly different after photorelease of 0.1-0.5 mM MgADP, but was reduced by 28-40% when 3.5 mM MgADP was added before photorelease of 0.5 mM MgADP. kADP was accelerated by about twofold when MgATP was varied from 0.5 to 8 mM MgATP. These effects of MgATP and MgADP were not readily accounted for by population of high force-producing states resulting from reversal of the ADP dissociation process. Rather, the results suggest that competition between MgADP and MgATP for crossbridges at the end of the cycle slows detachment leading to accumulation of force-generating crossbridges. Elevation of steady-state Pi concentration from 0.5 to 30 mM caused acceleration of kADP from 10.2 +/- 0.5 to 27.8 +/- 1.8 s-1, indicating that the tension rise involved crossbridge flux through the Pi dissociation step of the cycle.

Adenosine Diphosphate↗

PubMed1993

Maximum velocity of shortening in relation to myosin isoform composition in single fibres from human skeletal muscles.

1. Maximum velocity of shortening (Vmax) and compositions of myosin heavy chain (MHC) and myosin light chain (MLC) isoforms were determined in single fibres from the soleus or the lateral region of the quadriceps (vastus lateralis) muscles in man. Muscle samples were obtained by percutaneous biopsy, and membranes were permeabilized by glycerol treatment (chemical skinning) or by freeze-drying. 2. Types I, IIA and IIB MHCs were resolved from single fibre segments by 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and five different fibre types were identified: fibres containing type I MHC, types I and IIA MHCs, type IIA MHC, types IIA and IIB MHCs, and type IIB MHC. Only a few fibres co-expressed types I and IIA MHCs but 28% of all quadriceps fibres expressed both IIA and IIB MHCs in variable proportions. Fibres co-expressing types I and IIB MHCs were not found. 3. Alkali (MLC1 and MLC3) and dithio nitrobenzoic acid (DTNB) (MLC2) myosin light chains were observed in all type II fibres in variable proportions. MLC (MLC1s and MLC2s) isoforms from type I fibres had lower migration rates than the corresponding isoforms from type II fibres (MLC1f and MLC2f). More than half of type I fibres in both soleus (65%) and quadriceps (68%) muscles also expressed 'fast' MLC3 and 36% of the type II fibres from quadriceps muscle expressed the slow isoform of MLC2. 4. Differences were observed in some mechanical characteristics of freeze-dried versus chemically skinned fibres. Maximum tension (P0) and specific tension were lower in freeze-dried types I and IIA fibres than in chemically skinned, while no differences were observed in the IIA/B fibres. The numbers of types I/IIA and IIB fibres were too low to allow statistical comparisons. In chemically skinned fibres, mean specific tension (0.20 +/- 0.01 N/mm2) did not vary with fibre type. In freeze-dried fibres, on the other hand, specific tensions varied according to MHC type: higher (P < 0.01) specific tensions were observed in types IIB (0.19 +/- 0.01 N/mm2) and type IIA/B fibres (0.18 +/- 0.04 N/mm2) than in type I fibres (0.12 +/- 0.02 N/mm2). The specific tension of type IIA fibres (0.12 +/- 0.05 N/mm2) did not differ significantly from the other fibre types. Cross-sectional areas and mean Vmax did not differ between freeze-dried and chemically skinned fibres, either when all fibres were pooled or within respective fibre types. Vmax data from all fibres of a given type, irrespective of membrane permeabilization technique, have therefore been pooled.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1993

Influence of male rats on the luteinizing hormone-releasing hormone neuronal system in female rats: role of the vomeronasal organ.

Olfactory information processed by the vomeronasal system is reported to influence reproductive functions in a variety of mammals. The present studies were designed to determine if male-associated cues affect the luteinizing hormone-releasing hormone (LHRH) neuronal system, and, if so, to determine the extent to which these cues are processed by the vomeronasal organ (VNO). Ovariectomized rats underwent VNO removal (VNX) or sham surgery (VN-Sham). Forty-eight hours after estrogen priming (5 micrograms), they were subjected to one of the following treatments: repeated mating, repeated exposure to male-soiled bedding or repeated exposure to clean bedding. In animals treated for 180 min, coronal brain sections were double labelled for Fos protein and LHRH. An intense Fos immunoreactivity was induced following mating in the majority of LHRH neurons in the VN-Sham females, whereas removal of the VNO significantly suppressed the mating-induced Fos staining. Exposure of female rats to male-soiled bedding or clean bedding did not induce appreciable Fos immunoreactivity in LHRH neurons. Following 90 min of mating or exposure to bedding, blood samples were assayed for luteinizing hormone (LH). Mating stimulated the release of LH in VN-Sham females, while the removal of the VNO significantly suppressed the mating-induced LH release. Exposure of the females to male-soiled bedding or clean bedding did not induce an LH surge. The present results demonstrate that male-originating sensory cues (i.e. repeated mating) can influence the LHRH neuronal system, as evidenced by the presence of Fos immunoreactivity in LHRH cell bodies, and indicate that this effect is mediated through the VNO to a certain extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗