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Biomedical subjects

D A Taylor

Publications and source records attributed to D A Taylor.

At least 127 records · Page 7Linked to original sources
PubMed1989

Cytoplasmic Ca2+ is a primary determinant for myosin phosphorylation in smooth muscle cells.

Initiation of smooth muscle contraction is associated with Ca2+/calmodulin activation of myosin light chain kinase which catalyzes the phosphorylation of the 20-kDa light chain of myosin. In tracheal smooth muscle cells in culture, the extent of myosin light chain phosphorylation is less than 10% at basal cytosolic free Ca2+ concentrations of 150 nM. Stimulation of these cells with serotonin, histamine, carbachol, or the Ca2+ ionophore, ionomycin, increases free cytosolic Ca2+ concentrations and the extent of myosin light chain phosphorylation. Light chain phosphorylation reaches a maximal value of 67% at Ca2+ concentrations below 1 microM. The relationship between the extent of light chain phosphorylation and cytosolic free Ca2+ concentration is apparently independent of the source of free intracellular Ca2+ or the agent used to stimulate the cells and is not altered by pre-exposure of the contractile apparatus to high concentrations of free Ca2+. Pretreatment of cells with 8-bromo-cyclic GMP or forskolin decreases free cytosolic Ca2+ concentrations and the extent of myosin light chain phosphorylation in response to histamine or ionomycin. Pretreatment with 8-bromo-cyclic GMP also decreases the maximal extent of light chain phosphorylation. These results indicate that cytosolic free Ca2+ concentration, per se, is a primary determinant for myosin light chain phosphorylation in tracheal smooth muscle cells.

Animals↗
PubMed1989

The development and reversal of the tolerance to morphine in the longitudinal smooth muscle-myenteric plexus preparation of the guinea pig.

Chronic treatment with morphine results in a reduction in the potency of morphine in the longitudinal smooth muscle-myenteric plexus of the guinea-pig ileum. Implantation of morphine pellets leads to the development of tolerance to the inhibitory effects of morphine upon neurogenic contractions of this preparation. Tolerance develops within 24 hours, peaks between days 4 and 7 and disappears by day 14. A similar time course for the development of tolerance to the inhibitory effects of 2-chloroadenosine is also seen in these same morphine-tolerant preparations. The rate of reversal of morphine tolerance was assessed after the removal of the morphine pellets four days after implantation. In this situation, tolerance to the effects of morphine were maintained for at least 24 hours, were partially reversed at day 2 and were totally reversed by day 4. The delay in the development and reversal of the effect are consistent with the fact that chronic treatment with morphine evokes an adaptive sensitivity change.

2-Chloroadenosine↗
PubMed1988

Calcium dependence of myosin light chain phosphorylation in smooth muscle cells.

Smooth muscle cells grown in culture may provide a model system for studying the Ca2+ dependence of myosin light chain phosphorylation. Tracheal smooth muscle cells in culture had 60% of the myosin content of tracheal tissue. Western analysis with appropriate antibodies demonstrated one 20-kDa light chain and the presence of a 150-kDa myosin light chain kinase in both tracheal smooth muscle tissue and cells. Moreover, tracheal cells contained 74% of the myosin light chain kinase activity measured in tissue. Similar types of analyses of nonmuscle cells showed a much lower myosin and myosin light chain kinase content. Carbachol (10 microM) or ionomycin (10 microM) stimulation of fura-2-containing cells resulted in a rapid increase in cytosolic free Ca2+ concentration and in the extent of myosin light chain phosphorylation. Maximal increases in Ca2+ concentrations were greater with ionomycin than with carbachol (4400 versus 492 nM). Light chain phosphorylation increased after the Ca2+ concentration exceeded 200 nM from control values of 165 nM. Half-maximal phosphorylation (33%) occurred at 260 nM Ca2+. There was a similar relationship between free cytosolic Ca2+ concentrations and the extent of myosin light chain phosphorylation in carbachol- and ionomycin-stimulated cells. This relationship had a Hill coefficient of 2.7. These observations indicate that small changes in Ca2+ concentrations stimulate myosin light chain phosphorylation and thus presumably contraction in smooth muscle cells.

Animals↗
PubMed1988

Morphine tolerance and nonspecific subsensitivity of the longitudinal muscle myenteric plexus preparation of the guinea-pig to inhibitory agonists.

1. The sensitivity of the longitudinal smooth muscle/myenteric plexus (LM/MP) to agonists which reduce the amplitude of neurogenic contractions was studied in preparations obtained from animals implanted with either placebo or morphine (75 mg/pellet) pellets 7 days prior. 2. Tolerance or subsensitivity to morphine was observed following chronic treatment with morphine and was revealed as a rightward shift of the concentration-response curve to morphine. The degree of tolerance decayed modestly with time after removal from a morphine containing environment suggesting a time dependence for the loss of subsensitivity to morphine. 3. LM/MP preparations from animals pretreated with morphine also developed subsensitivity to the inhibitory effects of the purine analogue, 2-chloroadenosine. Subsensitivity to 2-chloroadenosine was seen as a parallel rightward shift of the concentration-response curve in morphine-tolerant preparations. The magnitude of the loss in sensitivity was comparable to that observed to morphine. 4. A reduction in sensitivity of the LM/MP following chronic treatment with morphine was also observed to the inhibitory effects of the alpha2 adrenoceptor agonists, clonidine and xylazine. In contrast to the results obtained with morphine and 2-chloroadenosine, the development of subsensitivity to alpha2 adrenoceptor agonists was characterized by a marked reduction in slope and a depression of the maximum response. 5. These data suggest that myenteric neurons possess spare receptors for morphine and 2-chloroadenosine but not for clonidine and xylazine. Furthermore, the studies support the idea that tolerance is associated with a general cellular change or adaptation which impacts on all of these inhibitory substances in such a way as to reduce their efficacy.

2-Chloroadenosine↗
PubMed1988

Calcium control of smooth muscle contractility.

Ca2+ is a primary second messenger that binds to an intracellular receptor protein, calmodulin. Increases in cytosolic Ca2+ concentration mediated by activation of cell surface receptors result in the formation of a Ca2+ calmodulin complex that regulates many Ca2+-dependent cellular processes. In smooth muscle, Ca2+/calmodulin activates myosin light chain kinase, which phosphorylates the regulatory light chain of myosin. This phosphorylation reaction increases the actin-activated MgATPase activity of myosin and is associated with increases in contractile properties, including force, stiffness, and maximal shortening velocity. These biochemical and biomechanical responses occur rapidly (seconds) in response to physiological stimulation involving neurotransmitter activation of smooth muscle cells. Thus, the Ca2+-dependent phosphorylation of the myosin light chain is a primary event in activation of smooth muscle contraction.

Actins↗
PubMed1988

Electron probe analysis of human skin: determination of the water concentration profile.

The water concentration profile across rapidly frozen human epidermis has been measured using electron probe analysis and analytical electron microscopy. Determinations were made within the cytoplasm of individual cells. From the basal layer, the water content remained relatively constant or decreased slightly across the viable tissue and decreased approximately linearly across the stratum corneum. A considerable discontinuity in water content occurred between these two regions over the stratum corneum-stratum granulosum junction and the last granular cell layer. The dominance of the water profile by a discontinuity suggests water loss is governed by a partitioning process, presumably a partitioning into the lipid domain. A water discontinuity offers important functional advantages in the conservation of substances within the body and in protection from intruding molecules.

Body Water↗
PubMed1988

Electron probe analysis of human skin: element concentration profiles.

Concentration profiles for the major biological inorganic elements Na, P, S, Cl, and K were measured across human skin using electron probe analysis and analytical electron microscopy. Determinations were made within the cytoplasm of individual cells. Uniform element concentrations were present throughout the viable tissue, whereas element profiles in the stratum corneum were considerably diverse. Phosphorus was practically absent from the stratum corneum. Sulfur (per unit volume) continuously increased from the inner to the outer cell layers of the stratum corneum largely as a result of cytoplasmic water loss as cells migrate to the surface. Potassium was essentially excluded from the inner stratum corneum. Very large gradients for K, Na, and Cl occurred from the middle of the stratum corneum to its outer surface; these gradients are likely the result of the inward diffusion of salts from sweat and could play a variety of physiological roles. The paucity of K and P within the inner stratum corneum suggests these important intracellular solutes (and perhaps others, including water) are recycled within the viable tissue, thus providing a virtual nutrient supply immediately underneath the stratum corneum. Alterations in this recirculation could have a regulatory function in the physiology of this tissue.

Chlorine↗
PubMed1988

Sensitivity of caudal arteries and the mesenteric vascular bed to norepinephrine in DOCA-salt hypertension.

This study was undertaken to determine what factors might contribute to arterial supersensitivity to norepinephrine associated with deoxycorticosterone acetate (DOCA)-salt hypertension in the rat. Experimental groups of male rats were uninephrectomized and 1 week later began receiving twice weekly injections of DOCA (20 mg/kg s.c. in sesame oil) plus 1% NaCl and 0.2% KCl in their drinking water. For each experimental group, a group of age-matched male rats underwent a sham operation and received injections of sesame oil and the NaCl-KCl drinking water. Perfused caudal arteries from 3-week-hypertensive rats were supersensitive to intraluminal and extraluminal norepinephrine administration. However, this difference in sensitivity between hypertensive and control caudal arteries was demonstrable at low rates of perfusion, 0.5 to 1.0 ml/min, but not at rates of 2.0 to 2.6 ml/min. The supersensitivity was not due to differences in neuronal uptake or to inhibition of extraneuronal uptake by DOCA. The perfused mesenteric vascular bed from 3- or 6-week-hypertensive rats was also supersensitive to intraluminal norepinephrine. However, the demonstration of supersensitivity in the mesenteric vasculature was independent of perfusion rate (2.3-6.8 ml/min) and perfusion pressure in the range of 30 to 60 mm Hg. There was little or no supersensitivity to transmural nerve stimulation in either the caudal artery or the mesenteric vasculature, a finding consistent with the observed decrease in endogenous norepinephrine content. Microelectrodes were used to determine resting membrane potential in the smooth muscle cells. No differences in resting membrane potential were detected between caudal or mesenteric arteries from hypertensive compared with control rats 2, 3, or 6 weeks after initiation of the DOCA-salt regimen. It is concluded that 1) the perfusion rate is a critical factor in designing experiments to test the sensitivity of caudal arteries to drugs, 2) the perfused mesenteric vascular bed is a useful preparation for studying sensitivity of blood vessels in hypertension, 3) the supersensitivity of blood vessels in the DOCA-salt model may be of greater importance relative to circulating catecholamines than to sympathetic innervation, and 4) the supersensitivity of blood vessels to norepinephrine in the DOCA-salt model is not due to changes in neuronal uptake, extraneuronal uptake, or membrane potential of the vascular smooth muscle cells.

Animals↗
PubMed1988

The effects of hyperstriatal lesions on one-trial passive-avoidance learning in the chick.

The roles of different forebrain structures in memory formation in the chick were investigated using restricted radio-frequency lesions. Young chicks will spontaneously peck at a small bright bead. If the bead has been coated with a distasteful substance, the chicks learn not to peck a similar bead on subsequent presentation. Thus, in a single trial chicks learn not to peck at an aversive stimulus. Bilateral lesions of the intermediate part of the medial hyperstriatum ventrale (IMHV) prevented the acquisition of this 1-trial passive-avoidance learning task. However, neither bilateral lesions of the lateral cerebral area (LCA) nor sham operation affected learning. IMHV has previously been shown to be critically involved in the learning process of imprinting in the chick. The present experiment demonstrates that the role of IMHV in learning is not restricted to imprinting. The function of IMHV in imprinting has been suggested to be concerned with the recognition of objects. In the present study sham-operated and LCA-lesioned chicks recognized the visual characteristics of the training bead and did not avoid a bead of a different color in the test. We propose that IMHV-lesioned chicks fail to learn the task because they are unable to recognize the visual characteristics of the training bead and consequently cannot make the association between the bead and the unpleasant taste.

Animals↗
PubMed1987

Biochemical markers of contraction in human myometrial smooth muscle cells in culture.

Phosphorylation of a light chain subunit of myosin by Ca2+ and calmodulin-dependent myosin light chain kinase is believed to be essential for smooth muscle contraction. The biochemical properties of the myosin phosphorylation system in human myometrial smooth muscle cells in monolayer culture were compared with those of human myometrial tissue and nonmuscle cells in culture. Native myosin was isolated from other cellular proteins of crude homogenates by polyacrylamide gel electrophoresis (in the presence of pyrophosphate) and quantified by densitometry. The myosin content of myometrial smooth muscle cells in culture and that of myometrial tissue were similar and four- to five-fold greater than that of human endometrial stromal cells or skin fibroblasts in culture. The specific activities of myosin light chain kinase in homogenates of myometrial smooth muscle cells that were maintained in culture and in myometrial tissue were similar (2.05 +/- 0.18 and 1.60 +/- 0.37 nmol phosphate incorporated per min per mg protein, respectively). On the other hand, enzyme activity in skin fibroblasts was only 5% of that in myometrial smooth muscle cells. Myosin light chain kinase activity in myometrial smooth muscle cells was dependent upon Ca2+ and was inhibited reversibly by the calmodulin antagonist, calmidazolium. The intracellular Ca2+ concentration measured by quin2 fluorescence was 0.12 microM in resting cells and increased in a concentration-dependent manner with KCl to a maximal value of 0.47 microM. These results indicate that biochemical processes important for smooth muscle contraction are retained in human myometrial smooth muscle cells in culture.

Calcium↗
PubMed1987

The cuing and priming of cognitive operations.

The effect on performance of advance information about the specific cognitive operations to be performed on a stimulus was investigated in two experiments using cues (information useful and necessary for performance) and primes (information useful but not necessary for performance). In the first experiment, a cue presented prior to a digit stimulus indicated whether the digit was to be classified as odd or even, or low (less than 6) or high (greater than 5). Results showed that performance improved with increasing time between cue and digit and with practice. A stroop-like asymmetric interference of the low-high operation on the odd-even operation was also observed. In the second experiment, a prime that matched the cue, mismatched it, or was neutral was presented before the cue. Results showed facilitatory and inhibitory priming effects, as well as a distance effect based on the position of a digit relative to the boundary between 5 and 6. The results of both experiments were discussed in terms of a model based on relative processing speeds of the two relevant properties of the digits.

Attention↗
PubMed1987

Evidence for tryptaminergic and noradrenergic involvement in the antisecretory action of morphine in the rat jejunum.

Experiments have been performed to determine whether the antisecretory (antidiarrhoeal) effect of morphine in the intestine is mediated by a direct action of morphine on enteric nerves. Rats were pretreated with 6-hydroxydopamine (6-OHDA) or p-chlorophenylalanine (PCPA) to deplete intestinal stores of noradrenaline and 5-hydroxytryptamine (5-HT). Intraperitoneal injection of 6-OHDA (3 doses at 50 mg kg-1) caused a selective reduction in the level of noradrenaline in the jejunum to 7.3% of control. Intraperitoneal injection of PCPA (200 mg kg-1) selectively reduced the jejunal level of 5-HT to 30.5% of control. Groups of rats that had been treated as described above were anaesthetized and then injected intravenously with saline or with blocking doses of either atropine (0.25 mg kg-1), hexamethonium (20 mg kg-1), ketanserin (30 micrograms kg-1), methysergide (30 micrograms kg-1), phentolamine (2 mg kg-1) or propranolol (1 mg kg-1). Following perfusion of the lumen of the jejunum, the rate of glucose absorption was measured to assess the integrity of the mucosa. Glucose absorption was unaltered in animals pretreated with hexamethonium and propranolol but there was a small enhancement in animals pretreated with atropine, PCPA, methysergide, 6-OHDA and phentolamine. The rate of net water absorption from the lumen of the jejunum and the rate of fluid secretion into the lumen following intra-arterial infusion of vasoactive intestinal peptide (VIP, 0.8 microgram min-1) were unaltered by any of the drug treatments. Intravenous injection of morphine (10 mg kg-1) did not alter the levels of noradrenaline or 5-HT in the whole jejunum. However, this dose of morphine did cause a 63.5% decrease in the VIP-induced change in water transport. This antisecretory effect of morphine was unaltered in animals pretreated with atropine, hexamethonium and propranolol. In contrast, methysergide, ketanserin and 6-OHDA abolished the antisecretory effect of morphine. PCPA and phentolamine produced a partial inhibition of morphine's antisecretory effect. It is concluded that morphine produces its antisecretory effect in the jejunum by activation of noradrenergic and tryptaminergic systems.

Animals↗
PubMed1987

Norepinephrine depletion and sensitivity changes in rat heart induced by pretreatment with reserpine.

Depletion of norepinephrine, sensitivity to isoproterenol and sensitivity to tyramine in rat atria were investigated after various doses and schedules of pretreatment of rats with reserpine. Virtually complete depletion of norepinephrine occurred in both right and left atria and ventricles after doses of 1.0 mg/kg/day of reserpine for one or more days of pretreatment. A smaller dose, 0.3 mg/kg/day, produced lesser depletion, and a larger dose, 2.5 mg/kg/day, caused severe central nervous system depression and high mortality. Chronic treatment (5 days or longer) with the 1.0-mg/kg/day dose produced supersensitivity of right atria to the chronotropic, but not inotropic, responses to isoproterenol. Chronic treatment with this dose for 7 days produced inotropic supersensitivity in left atria. Most of the schedules of pretreatment with reserpine depressed the maximum response to tyramine. However, the data indicate that the tyramine-releasable norepinephrine was not a consistent reflection of the total norepinephrine pool, even when depletion was very pronounced. The effects of depletion of cardiac stores of norepinephrine with reserpine in comparison with the effects of cardiac sympathectomy are discussed.

Animals↗
PubMed1987

Characteristics of adaptive supersensitivity in the left atrium of the guinea pig.

Chronic pretreatment of guinea pigs with reserpine (0.1 mg/kg/day for 7 days) induces inotropic supersensitivity in left atria. The sensitivity is increased to isoproterenol, norepinephrine, 5'-guanylylimidodiphosphate and forskolin, and the maximum response is increased to the partial agonist albuterol. These results, coupled with data in the literature, suggest that adaptive supersensitivity in the guinea pig heart is due to a change in one or more of the components of the adenylate cyclase system that is specifically coupled to beta adrenoceptors. The results indicate that the supersensitivity is demonstrable when the concentration-response curves for agonists are determined in isolated whole left atria but not when they are determined in strips cut from left atria. This explains a discrepancy in the literature. It is suggested that cellular changes, possibly in electrolyte distribution, resulting from the additional manipulation of cutting the atria into slices obscure the sensitivity difference between the control and experimental tissues.

Albuterol↗
PubMed1986

Antagonism by some ergot derivatives of 5-HT-induced vasoconstriction.

The ability of a number of ergot derivatives to inhibit 5-hydroxytryptamine (5-HT)-induced vasoconstriction was examined in the perfused rat mesenteric artery preparation. 5-HT produced an increase in perfusion pressure indicative of vasoconstriction. The ergot derivatives inhibited the 5-HT-induced vasoconstriction in a manner that was predominantly not competitive in nature. As 5-HT2 antagonists the ergot derivatives ranged in potency from CQ 32-084 which abolished the 5-HT2 receptor mediated response at a concentration of 10 nM to LY-141865 which was inactive up to a concentration of 10 microM.

Animals↗