Biomedical subjects

K Hermsmeyer

Publications and source records attributed to K Hermsmeyer.

At least 55 records · Page 3Linked to original sources

PubMed1988

Intracellular Ca2+ release in vascular muscle cells by caffeine, ryanodine, norepinephrine, and neuropeptide Y.

Distribution of intracellular free calcium concentration, (Ca2+)i, in living cells has been measured with submicron resolution in isolated, single vascular muscle cells from neonatal Wistar-Kyoto (WKY) rats. The experiments were carried out on cells loaded with fura-2 using a digital photon-counting camera (PMI VIM) with computer analysis of 16-bit images. Determination of the fluorescence intensity at 360 nm excitation allowed correction for a nonhomogenous intracellular fura-2 dye distribution and revealed areas with high calcium concentrations (hot spots, HS) associated with putative sarcoplasmic reticulum (SR), even in nonactivated cells. Investigation of the effects of caffeine and ryanodine revealed that caffeine activates both centrally and peripherally located SR to release calcium, while ryanodine preferentially acts on peripherally located SR, presumably to lock calcium channels of the SR in an open state. The interaction of calcium release and uptake mechanisms in excitation-contraction coupling is supported by intracellular calcium distributions during spontaneous contraction and relaxation, which suggest a pattern of calcium release from peripherally located SR followed by release from centrally located SR. Additional studies on the effects of neuropeptide Y and norepinephrine virtually rule out any potentiation of norepinephrine by neuropeptide Y via direct modulation of (Ca2+)i in vascular muscle cells.

Alkaloids↗

PubMed1987

Halothane relaxes previously constricted isolated porcine coronary artery segments more than isoflurane.

Coronary vasodilation by halothane and isoflurane were compared using in vitro tension recording. Porcine left anterior descending coronary arterial segments (1.5-2.0 mm o.d.) were constricted with either K+ (30 mM) or prostanoid U44069 (6 X 10(-7) M) in the absence of other drugs or anesthetics. Following stabilization of constriction, arteries were exposed to halothane or isoflurane at 0.5, 1.0, 1.5, 2.0, and 3.0% concentrations. K+ (30 mM) induced constriction was reduced by halothane at 1.5, 2.0, and 3.0% and U44069 (6 X 10(-7) M) induced constriction was reduced at 0.5, 1.0, 1.5, 2.0, and 3.0%. K+ (30 mM) induced constriction was reduced by isoflurane only at 3.0% and U44069 (6 X 10(-7) M) induced constriction was reduced by isoflurane only at 2.0 and 3.0%. U44069 induced constriction was more susceptible than K+ induced constriction to relaxation by halothane or isoflurane. Halothane was more potent than isoflurane as a direct relaxant of porcine epicardial left anterior descending arterial segments previously constricted with K+ (30 mM) or U44069 (6 X 10(-7) M).

Animals↗

PubMed1987

Felodipine actions on vascular muscle Ca2+ channels.

Felodipine is a potent, but relatively slow, relaxation agent in rat caudal artery, decreasing 30 mM K+ contractions by 39% at a concentration of 1 nM and 88% at 10 nM. Membrane potential at rest was unchanged, but 10 nM felodipine caused a 5 mV hyperpolarization of vascular muscle cells previously depolarized by 30 mM K+. Felodipine selectively decreased the sustained, but not the transient, type of calcium current in a whole-cell voltage clamp of azygos venous muscle cells. Relaxation by felodipine was additive to that caused by 10 microM trifluoperazine, a calmodulin antagonist, arguing against an action of felodipine via calmodulin. The vascular muscle relaxant effects of felodipine appear to be explainable by blockade of the sustained type of calcium channels.

Animals↗

PubMed1986

Calcium and sodium channels in spontaneously contracting vascular muscle cells.

Electrophysiological recordings of inward currents from whole cells showed that vascular muscle cells have one type of sodium channel and two types of calcium channels. One of the calcium channels, the transient calcium channel, was activated by small depolarizations but then rapidly inactivated. It was equally permeable to calcium and barium and was blocked by cadmium, but not by tetrodotoxin. The other type, the sustained calcium channel, was activated by larger depolarizations, but inactivated very little; it was more permeable to barium than calcium. The sustained calcium channel was more sensitive to block by cadmium than the transient channel, but also was not blocked by tetrodotoxin. The sodium channel inactivated 15 times more rapidly than the transient calcium channel and at more negative voltages. This sodium channel, which is unusual because it is only blocked by a very high (60 microM) tetrodotoxin concentration but not by cadmium, is the first to be characterized in vascular muscle, and together with the two calcium channels, provides a basis for different patterns of excitation in vascular muscles.

Animals↗

PubMed1986

Membrane potential, Ca2+ influx, and Ca2+ release in single vascular muscle cells.

Isolated single vascular muscle cells from azygous vein of rats were used to make measurements of intracellular Ca2+ release, using a differential interference contrast 2 wavelength system and the Ca2+ indicator arsenazo III (Az III). Ca2+ release in spontaneously contracting isolated single muscle cells was extremely nonuniform, giving Ca2+ signals in some areas that were at least five times as great as those in others. Some areas of the cell showed virtually no detectable increase in Ca2+ activity during contraction, and these differences in Ca2+ activity corresponded with differences in contractile filament movement within the cell. The possibility that the nonuniformity of the Ca2+ signals was due to localization of Az III, which had been introduced by liposomes, was excluded because optical density at the 580 nm isosbestic point in any 5-20 micron 2 area varied by not greater than 50% from the average Az III concentration. In contrast, when isolated single vascular muscle cells were stimulated with electric current pulses, Ca2+ release and contraction were uniformly synchronized throughout the cell. Our data suggest that the uptake and removal process by intracellular transport is the major determinant of intracellular Ca2+ activity in azygous venous vascular muscle cells.

Animals↗

PubMed1986

Membrane ATPase mechanism of K+-return relaxation in arterial muscles of stroke-prone SHR and WKY.

These studies compared the importance of electrogenic Na+-K+ active (ATP driven) transport, changes in K+ conductance, and passive Ca2+-Na+ countertransport in the large relaxation that occurs in the rat caudal and basilar artery on return to K+ from K+-free solutions. Furthermore, we compared the importance of these three membrane electrical mechanisms in stroke-prone spontaneously hypertensive rats (SP-SHR) versus their normotensive Wistar-Kyoto control rats (WKY) in basilar (cerebral) and caudal arteries. We found that in both basilar and caudal arteries the hyperpolarization and relaxation that occurred on return to K+ after exposure to a 0 K+ (extracellular) solution was consistently greater in SP-SHR than in WKY. The change in membrane potential occurring on transition to 0 K+ in arteries maintained at low temperature (16 degrees C), used as an estimate of the change in K+ conductance during the K+ transition, was not different in either basilar or caudal arteries between SP-SHR and WKY. Thus the hyperpolarization on return to K+ at body temperature would depend primarily on the level of activity of the membrane ATPase, referred to as the Na+ pump. We also sought to compare the passive (but electrogenic) Ca2+-Na+ countertransport mechanism between strains for both arteries, but we were unable to detect any evidence of the predicted hyperpolarization-contraction on transition from 145 to 10 mM extracellular Na+. Furthermore, the return to extracellular Na+ solution failed to show the depolarization-relaxation predicted by the Ca2+-Na+ countertransport mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗

PubMed1986

Differential reactivity to 5-hydroxytryptamine in canine coronary arteries.

Responses to 5-hydroxytryptamine (5HT) were compared in large [2.1-3.0 mm outside diameter (OD)], medium (1.5-1.8 mm OD) and small (0.5-1.0 mm OD) isolated canine coronary arteries. 5HT produced contraction of large and medium arteries, with the maximal response averaging 35.1 +/- 4.0 and 21.0 +/- 3.3%, respectively, of the contraction to 100 mM KCl. Endothelial removal increased the response to 5HT, with the maximal response averaging 43.6 +/- 12.6 and 32.4 +/- 7.5%, respectively, of the 100 mM KCl contraction. Small arteries did not contract significantly to 5HT in the presence or absence of endothelium. However, 5HT (10(-6) M) contracted small arteries that were contracted with 30 mM KCl, averaging 130 +/- 3% of the original contraction to KCl. This further contraction to 5HT was slightly potentiated by removal of the endothelium. We conclude that, unlike larger epicardial arteries, coronary arteries less than 1 mm OD are unresponsive to 5HT under resting conditions. Failure of small arteries to contract to 5HT cannot be explained by an inhibitory influence of the endothelium. However, 5HT enhances the contraction of small arteries to K+, and this response tends to be augmented by endothelial removal.

Animals↗

PubMed1986

Calcium channels in muscle cells isolated from rat mesenteric arteries: modulation by dihydropyridine drugs.

The patch clamp technique was used to make whole-cell recordings of calcium channel currents from single muscle cells freshly isolated from rat mesenteric arteries. The cells were found to contain two types of calcium channels; one type is activated by small depolarizations and inactivates quickly, whereas the other requires stronger depolarizations for activation and inactivates more slowly. Nitrendipine blocked the second type of channels with a potency that depended on membrane potential. Interpreted by a modulated receptor hypothesis, these results suggest that nitrendipine binds to the inactivated state of the channel with a KD of about 0.5 nM, similar to concentrations effective in relaxing blood vessels. The magnitude of the calcium channel current was small compared with other excitable cells, but the "calcium agonist" drug BAY K8644 produced a 10-fold augmentation of calcium channel current, suggesting the existence of a large "reserve" of calcium channel current.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1985

Vasopressin induced rhythmic activity in rat basilar artery.

The effects of vasopressin on membrane potential and tension were studied in isolated segments of basilar arteries from the University of Iowa colonies of normotensive inbred Kyoto-Wistar rats (WKY) and stroke-prone spontaneously hypertensive rats (SP-SHR). In the presence of vasopressin (0.01-0.3 IU/ml), basilar arteries from WKY, but not from SP-SHR, developed rhythmic contractions. These contractions were recorded in 13 of 14 WKY basilar arteries, were unaffected by pretreatment with 6-hydroxydopamine, and were characterized by 20-100 dyne oscillations in tension, occurring 1-3 cycles/min, and superimposed on the vasopressin-induced contraction (averaging 60 dynes at 0.01 IU/ml or 160 dynes at 0.3 IU/ml). However, resting membrane potentials were not different in SP-SHR vs. WKY at 37 degrees C, and both strains showed about the same (11 mV) depolarization by 0.1 IU/ml of vasopressin. The rhythmic contractions were enhanced by K+-free solution, and abolished in the presence of high K+ solution (30 mM), suggesting that active Na+-K+ transport may be involved in modulating the rhythmic activity. These findings are consistent with the hypothesis that the vasopressin-induced rhythmic contractions in WKY basilar arteries are at least partly dependent on a reduced activity of electrogenic Na+-K+ active transport in WKY as compared to SP-SHR.

Animals↗

PubMed1985

Altered membrane potential control of contraction in arterial muscle in hypertension.

Membrane potential has a different origin in the Kyoto-Wistar spontaneously hypertensive rat (SHR) arterial muscle cells compared to the normotensive Wistar-Kyoto rat (WKY) because of a higher activity of the electrogenic Na+ pump (Na+/K+-ATPase) in SHR. The activity of the Na+ pump is probably a good indicator of the state of Na+ loading of the vascular muscle cells, and is likely to be a partial compensation for increased SHR Na+ loading. The coupling mechanism might be altered due to excess intracellular free Na+ and diminished intracellular free K+, to a more electrogenic ratio of 3. The cause of higher intracellular Na+ and the resulting changes in Na+ transport is unknown, but there appears to be a trophic (long-term) influence of the sympathetic nervous system playing a key role, as shown by cross-innervation experiments.

Animals↗

PubMed1984

Altered arterial muscle ion transport mechanism in the spontaneously hypertensive rat.

The cellular mechanisms that appear to contribute to increased contraction in hypertension involve altered ion movements through cell membranes. The K+ and Na+ gradients and the active transport of Na+ and K+, sometimes electrogenic, are important for the peripheral arteries. There may be other kinds of transport involved, especially the active transport of Ca2+. However, a passive Ca2+-Na+ countertransport mechanism has not been demonstrated in vascular muscle and therefore presently appears unlikely as an explanation of hypertension. The altered transport of Na+ and K+ apparently plays a causative role in the development of hypertension, because there is a cross-over of membrane properties on cross-innervation. Since the prevention of sympathetic innervation prevents that cross-over, it is likely that a long-term influence of the sympathetic nervous system is important in the development of hypertension. The trophic influence of the sympathetic innervation on vascular muscle is now one of the important frontiers in the study of cellular mechanisms that lead to increased blood pressure.

Animals↗

PubMed1984

In vitro adrenergic and cholinergic innervation of the developing rat myocyte.

We studied the development of selective adrenergic and cholinergic neuroeffector transmission in primary cultures of isolated ventricular muscle cells. Explants of either thoracolumbar sympathetic ganglia or sacrococcygeal spinal cord were added to newborn rat ventricular cultures harvested prior to the onset of in vivo autonomic innervation. Neuronal growth, migration, and the formation of neuromuscular junctions were observed with light and scanning electron microscopy. Glyoxylic acid histofluorescence, reflecting catecholamine synthesis, was found in only the sympathetic neuromuscular cultures. Choline acetyltransferase activity was detected in both spinal cord and sympathetic neuromuscular cultures, but was significantly higher in the spinal cord neuromuscular cultures. The isolated ventricular muscle cells remained at a constant spontaneous contraction frequency, regardless of the type of culture preparation. Guanethidine sulfate application produced a positive chronotropic response, blocked by propranolol, in the sympathetic neuromuscular cultures, but not in the spinal cord neuromuscular cultures. Bethanechol sulfate produced a negative chronotropic response, blocked by atropine, in the spinal cord neuromuscular cultures, but not in the sympathetic neuromuscular cultures. Isolated ventricular muscle cells in the absence of neurons failed to respond to either agent. Direct microelectrode stimulation of adrenergic or cholinergic neurons likewise respectively produced either a positive or negative ventricular muscle cell chronotropic response. These studies are the first to establish the selective production of functional cholinergic and adrenergic innervation of isolated cardiac muscle cells in vitro.

Adrenergic Fibers↗

PubMed1984

The isolated sinoatrial node cell in primary culture from the newborn rat.

We prepared primary cell cultures of the sinus node region from newborn rat hearts. Sinoatrial node cells were easily distinguished from the other cardiac muscle cells and nonmuscle cells in culture by size, configuration, and rapid, attenuated spontaneous contractions (185.0 +/- 8/min, mean +/- SEM). The spontaneously contracting sinoatrial node cells were extremely sensitive to acetylcholine and norepinephrine, responding to concentrations at least 1000-fold less than other cardiac muscle cells. These same sinoatrial node cells in culture were fixed and precisely relocated by either subsequent scanning or transmission electron microscopy. The ultrastructural features of these sinoatrial node cells in culture were similar to those observed in the cells of intact sinus node sections from the source hearts. This study is the first to present single, spontaneously active, neonatal sinoatrial node cells maintained in vitro with morphological and functional properties desirable for physiological investigations.

Animals↗

PubMed1984

Calcium antagonists and excitation of the vascular muscle membrane.

Several mechanisms of action for Ca2+ antagonists are possible at the vascular muscle cell membrane and at subsequent steps. In rat caudal artery, nitrendipine hyperpolarizes the resting vascular muscle cell, an action different from that of verapamil. Hyperpolarization might be expected to explain the relaxant action of nitrendipine because hyperpolarization per se causes a decrease in Ca2+ influx. SHR vascular muscle cells show a greater dependence on extracellular K+ concentration for the action of nitrendipine than WKY, as indicated by both tension and membrane potential measurements, suggesting an action on an ion pump. It is possible to directly test the hypothesis that inhibition of Ca2+ influx can directly account for the entire effect of nitrendipine by determination of intracellular Ca2+ with the metallochromic absorbence dye, arsenazo III. Nitrendipine not only decreased the magnitude of the Ca2+ signal but also enhanced the return to resting, or below resting, intracellular Ca2+ levels. Experiments on isolated single cells from the azygous vein of neonatal rats showed evidence of both blockade of Ca2+ influx and enhancement of Ca2+ efflux. These measurements suggest that nitrendipine might cause relaxation by stimulating Ca2+ efflux as well as by decreasing passive Ca2+ influx. Therefore, the action of nitrendipine might be more complicated than simply blocking Ca2+ channels, possibly involving stimulation of active ion transport.

Animals↗

PubMed1984

Difference in vasopressin-induced contraction of basilar arteries from stroke-prone spontaneously-hypertensive rats (SP-SHR) and control Wistar-Kyoto rats (WKY).

Vasopressin (0.01-0.3 IU/ml) contracted isolated segments of rat basilar arteries from stroke-prone SHR (SP-SHR) and normotensive Wistar-Kyoto rats (WKY) unequally. Basilar arteries from SP-SHR were more responsive to vasopressin than were those from WKY when adrenergic nerve endings were present in both preparations. After destruction of adrenergic nerve endings by in vitro 6-hydroxydopamine treatment, the ED50 for vasopressin in both WKY and SP-SHR arteries decreased by a factor of three, indicating that the contractions caused by vasopressin were similarly modulated by prejunctional neurotransmitter release. However, only arteries from WKY showed prominent rhythmic relaxation-contraction cycles superimposed upon the vasopressin-induced tone. The tension cycles were 20-100 dyn in amplitude and occurred at 1-3 cycles/min. These tension oscillations of WKY were pronounced and obvious, sometimes amounting to as much tension as the underlying tonic contraction. Tension cycles could reflect a physiological contraction-relaxation phasing mechanism that fails to occur in basilar arteries of SP-SHR. The rhythmic activity was enhanced by K+-free solution and abolished by 30 mM K+ solution, suggesting that pacemaker changes in K+ conductance may underlie the WKY tension oscillations. It is suggested that the absence of rhythmic contractions in SP-SHR basilar arteries may be explained by greater activity of the electrogenic Na+-pump, which would tend to prevent the rhythmic oscillations in tension. These observations suggest that vasopressin has a differential action on basilar arteries of SP-SHR and WKY.

Adrenergic Fibers↗

PubMed1983

Excitation of vascular muscles by norepinephrine.

The mechanism by which norepinephrine causes excitation of vascular muscle is a concept that has undergone considerable change in the last several years. Although the excitation step is absolutely fundamental to understanding constriction and dilation of arteries, several aspects of the hypothesis are not well understood and have recently been controversial. The earliest view of the excitation process was that action potentials propagate uniformly along the arterial wall, just as fast skeletal muscle, and was disproved early in recording of electrical events from blood vessel walls. The view that then emerged was that membrane potential acts as an analog signal controlling contraction through graded depolarization which, unlike that found in fast skeletal or cardiac muscle, could be maintained for minutes or even hours. This concept of graded depolarization and graded contraction has served as the best model of the vascular muscle excitation process for about 20 years. However, questions have been raised about the importance of membrane potential as a control mechanism because of reports of noncorrelations between membrane potential and tension. The controversy centers around two alternate proposals for the excitatory action of norepinephrine. The proposal of the noncorrelation group is that mechanisms other than membrane potential exert the major control over contraction, perhaps with spatially specialized receptors such that only those areas near nerve endings would cause depolarization as part of the event initiating contraction. On the other hand, the proposal by the strong correlation group would be that membrane potential is the dominant control mechanism. Where experiments have been carried out to specifically test the existence of a noncorrelation between membrane potential and contraction, no failure of correlation was found. The fundamental problem in each instance of a noncorrelation appears to be the attempt to record tension from one part of an artery and membrane potential from another part, which is assumed to behave as an electrically and mechanically homogeneous unit. However, direct measurements of localized areas of the blood vessel wall show such an assumption to be unjustified. In fact, cell-to-cell conduction of an electrical signal to synchronize the blood vessel could not be supported in experiments using refined intracellular and extracellular recording methods.+2

Action Potentials↗

PubMed1983

Tetrodotoxin-sensitive Na+ channels in isolated single cultured rat myocardial cells.

We studied the existence of tetrodotoxin (TTX)-sensitive fast Na+ channels in isolated single (verified by dye injection) myocardial cells compared with small multiple-cell groups from 1- to 3-day-old rat ventricles in cell culture. For single cells, average values were -63 mV maximum membrane potential, 32 mV overshoot, and 65 V/s maximum rate of rise of the action potentials (+Vmax). These values were comparable to values from groups of multiple (2-10) cells. TTX strongly depressed +Vmax dose dependently, with no difference between single and multiple cells. +Vmax was also decreased by lowering extracellular Na+ concentration but not by D 600 or lowering extracellular Ca2+ concentration. These results suggest that 1) isolated single cells possess TTX-sensitive fast Na+ channels, 2) culturing per se does not alter TTX sensitivity, and 3) TTX sensitivity is not modified by cell density.

Action Potentials↗

PubMed1983

Sodium pump hyperpolarization-relaxation in rat caudal artery.

Electrogenic ion transport contributes vitally to the Em in vascular muscle and thus is an important influence on contraction and relaxation. Agents that act on membrane ion transport will cause depolarization or hyperpolarization of sufficient magnitude to cause contraction or relaxation, respectively. In the caudal artery of the rat, the principal ion involved appears to be Na+. The transport process appears to be the Na+, K+-ATPase, which is ouabain sensitive, rather than other possible candidates such as the Na+-Ca2+ countertransport mechanism. The hyperpolarization and parallel relaxation found in caudal artery on return to K+ provide unequivocal evidence for an electrogenic Na+ pump. In contrast, the lack of a contraction on transition to O Na+ suggests that the caudal artery does not show an Na+-K+ countertransport system. Although other ion transport systems might be established later for caudal artery and other kinds of vascular muscle, it now appears that the electrogenic Na+ pump is the main ion transport system controlling contraction through a continuous contribution to Em.

Animals↗