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K Hermsmeyer

Publications and source records attributed to K Hermsmeyer.

At least 37 records · Page 2Linked to original sources
PubMed1992

Subcellular distribution of hydralazine in rat single vascular muscle cells.

High specific activity (20 Ci/mmol) tritiated hydralazine (3Hyd) distribution in isolated, cultured vascular muscle cells was determined to identify the sites of Hyd binding. 3Hyd dose-dependently bound to extracellular protein and to the area of organelles which secrete these proteins. Increased extracellular binding after Hyd pre-exposure suggests new binding sites may be exacerbated as a result of Hyd interactions. These experiments suggest a potentially important feature of the mechanism of action of this directly acting vasodilator.

Animals↗
PubMed1992

Modification of platelet and lymphocyte calcium handling and blood pressure by dietary sodium and calcium in genetically hypertensive rats.

Abnormal cellular calcium handling has been postulated to be involved in the pathogenesis of hypertension. To determine whether the blood pressure response to dietary manipulation of sodium level (as the chloride salt) and calcium level is associated with changes in cellular cation metabolism, the interactive effects of both dietary components on blood pressure and intracellular free calcium concentration [( Ca2+]i) in blood platelets and thymic lymphocytes, erythrocyte sodium content, and blood ionized calcium were examined in stroke-prone spontaneously hypertensive rats. Rats were fed low (0.3%) or high (3.1%) sodium and low (0.2%) or high (2.0%) calcium diet for 6 weeks. With the rats receiving the high sodium-low calcium diet, systolic blood pressure was higher than with other diets, among which no difference was detected. Both basal [Ca2+]i and ionomycin (50 and 150 nmol/L) stimulated [Ca2+]i in platelets, and in lymphocytes, were higher with the high sodium-low calcium diet than with the others. Thus the high sodium diet elevated blood pressure and increased [Ca2+]i in the resting and stimulated state in both cell lines with the low-calcium but not the high-calcium diet. The high-sodium diet was associated with increased sodium content of erythrocytes, whereas manipulations of dietary calcium level had no effect on erythrocyte sodium content. Dietary calcium level had more of an effect on blood ionized calcium than did dietary sodium level. In combined diet groups, blood pressure was positively, significantly correlated with basal and ionomycin-induced [Ca2+]i in platelets (r = 0.64 and 0.67, respectively) and in lymphocytes (r = 0.53 and 0.60, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1991

Modulation of intracellular calcium by potassium channel openers in vascular muscle.

We investigated two putative K+ channel openers, pinacidil and BRL34915 (cromakalim), and demonstrated their vasorelaxant effectiveness on rat artery contractions induced by K+, tetraethylammonium (TEA), or norepinephrine. The K+ channel opener-induced decrease in tension was rapid, even when tension was stimulated by 100 mmol/l K+. Measurements of intracellular free Ca++ (activity) by ultra-high sensitivity digital imaging microscopy was carried out by briefly loaded fura 2 (fluorescence ratio) quantitation in isolated, contracting cells of rat azygos vein. Submicron resolution was achieved by measuring cytoplasmic Ca(++)-sensitive fluorescence at each pixel, and size and intensity of areas with high Ca++ concentrations, called hot spots, were determined by a computer-generated, 3 lambda algorithm. Hot spots, which most likely represent the sites of Ca++ release and re-uptake by Ca(++)-regulatory organelles, increased in size and intensity upon addition of K+ or norepinephrine, reaching an early peak prior to the whole cell average peak in cytoplasmic Ca++ activity. Both norepinephrine and K(+)-induced stimulation resulted in Ca++ activity increases that were primarily due to Ca++ release from storage sites. Reduction of free Ca++ activity to resting or lower levels occurred upon addition of pinacidil or cromakalim. Intracellular Ca++ decreases due to K+ channel openers appeared abruptly beginning at the central portions of the cells, resulting in a pronounced early drop in central Ca++ activity while elevated Ca++ levels persisted at the periphery. While this late stage residual of peripheral Ca++ appears to be a significant step in the vascular muscle relaxant action of both K+ channel opener drugs, the level of Ca++ at peripheral sites was greater in response to pinacidil than to cromakalim. The results of this study suggest that in addition to increasing K+ conductance, pinacidil and cromakalim cause 1) decreased Ca++ activity in central regions of the myocytes, and 2) a shift in Ca++ distribution to primarily subsarcolemmal sites. These observations lead us to hypothesize separate control of peripheral and central Ca++ activity within a vascular muscle cell, with Ca++ redistribution that can be altered by vasorelaxants. We suggest that intracellular Ca++ redistribution may contribute the membrane potential-independent part of the vasorelaxant action of the K+ channel openers.

Animals↗
PubMed1991

Differences of calcium channels in vascular muscle in hypertension.

Recent investigations on the role calcium channels in the activation of vascular muscle suggest that calcium channels act in the capacity of voltage sensors in the excitation-contraction (EC) coupling sequence, rather than acting merely as gateways for calcium influx. In this study, recordings were made of calcium currents under various conditions using voltage-clamp techniques and isolated vascular muscle cells of spontaneously hypertensive rats (SHR) and genetically matched, normotensive Wistar-Kyoto (WKY) rats. Vascular muscle cells from azygos veins showed both transient (T), and long-lasting (L) currents in all of the spontaneously active cells studied. The ratio of L-type to T-type currents was greater in SHR than in WKY controls, even though the cells studied were from the venous side in newborn animals, in which there are no differences in either arterial or venous blood pressure. Data suggest that there are enhanced L-type calcium currents in SHR compared to WKY controls even in the prehypertensive state and that, in this form of gentic hypertension, there are fundamental changes in the membrane signal that triggers contraction. Diltiazem showed a preferential effect on blocking the L-type calcium channels, beginning at 100 pmol/L. At levels of 1 nmol/L to 1 mumol/L, diltiazem blocked L-type calcium current without a detectable effect on gating currents or on T-type calcium current. These findings may indicate fundamental differences between vascular muscle and cardiac muscle channel gating processes.

Animals↗
PubMed1991

Subcellular localization of calcium release in isolated rat myocardial cells.

Independent determinations of Ca2+ by two indicators showed that subcellular Ca2+ activity (intracellular free calcium concentration) was heterogeneous in rat myocardial cells. Arsenazo III (Az III), a membrane-impermeant absorbance indicator for Ca2+, was loaded into cardiac muscle via liposomes and calcium quantitated at two wavelengths through a focal point diaphragm in 5-100 microns 2 regions by a photometer. Fura-2, a high-affinity fluorescent calcium indicator, was loaded into cells as the ester form, and the light intensity was measured by digital-imaging microscopy using a photon-counting camera. Calcium activity at each picture element was quantitated by division of fluorescence excited by two ultraviolet wavelengths, and corrected for concentration differences in fura-2 by a third, Ca(2+)-insensitive wavelength. Both methods revealed hot spots of Ca2+ release and uptake that could be enlarged, added to, or altered. Addition of 1-10 nM norepinephrine caused up to a 500% increase in Ca2+ in localized regions, although whole cell average Ca2+ increased by only 0-80%, suggesting the importance of localized intracellular Ca2+ release for contraction.

Animals↗
PubMed1990

Effects of dietary calcium on nimodipine-sensitive calcium channel function in stroke-prone spontaneously hypertensive rats.

We studied the effects of dietary Ca2+ on blood pressure, survival, and calcium channel function to investigate cardiovascular disease mechanisms in stroke-prone spontaneously hypertensive rats. Beginning at 3 weeks of age, rats were fed high sodium chloride diets (8.0%) in combination with either high (2.0%) or low (0.2%) Ca2+ diets for 8 weeks. At 12 weeks of age, survival was 90% in the high Ca2+ group and 30% in the low Ca2+ group. The higher blood pressure and lower survival in the low Ca2+ group suggest an intensification of altered vascular muscle cell mechanisms by a dietary Ca2+ deficit. Nimodipine (1-10 nM) effectively blocked L-type Ca2+ currents in isolated vascular muscle cells from both groups. Contraction of isolated cells that were not patch clamped to high potassium solutions were also blocked by 1 nM nimodipine. Disappearance of the L-type Ca2+ channel current was accelerated by holding at depolarizing potentials (positive to -50 mV) and by depolarizing steps to 0 mV. Nimodipine block of the L-type Ca2+ currents in vascular muscle is believed to contribute substantially to antihypertensive properties and stroke prevention, actions that may develop fully only in stroke-prone spontaneously hypertensive rats on a diet of at least normal Ca2+.

Animals↗
PubMed1989

Cellular calcium regulation in hypertension.

In vascular muscle cells, two distinct types of functionally important calcium (Ca2+) channels, called transient (T) and sustained (L), are differentiated by dihydropyridine calcium antagonists (CaA). We studied the ratio of T/L Ca2+ channels in isolated, spontaneously contracting azygous venous cells of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) by quantitating Ca2+ currents and intracellular Ca2+ release. While total transmembranous Ca2+ current was not different between the two strains, the proportion of Ca2+ currents carried by L-type channels was enhanced in vascular muscle cells from SHR. We have recently compared subcellular distribution of intracellular free Ca2+ concentration in the same cells, at rest and during stimulation, by quantitation with a digital photon-counting camera. Fura-2 fluorescence intensity showed that Ca2+ release was principally from sarcoplasmic reticulum and that cells from SHR had higher levels of Ca2+ upon calcium channel stimulation, especially at the cell periphery. These findings suggest fundamental differences in SHR and WKY vascular muscle cells implicating the importance of changes in calcium channels, modulation of Ca2+ release, and Ca2+ uptake in SHR hypertension.

Animals↗
PubMed1989

Intracellular vascular muscle Ca2+ modulation in genetic hypertension.

Distribution of intracellular free calcium concentration (Ca2+) was compared in spontaneously hypertensive rat (SHR) and Wistar-Kyoto (WKY) rat isolated vascular muscle cells at rest and during stimulation by K+ with Ca2+ agonist or antagonist. Ca2+ activity was quantitated at each point within vascular muscle cells loaded with fura-2 at fluorescence excitation wavelengths of 340, 360, and 380 nm, and fluorescence emission at 510 nm (all filters were +/- 5 nm) quantitated by a digital photon-counting camera. Measurements of fluorescence intensity ratio in central and subsarcolemmal areas showed that calcium release, in response to 30 or 100 mM K+ with Ca2+ agonist or during spontaneous contractions, was principally from sarcoplasmic reticulum. Addition of the Ca2+ agonist Sdz 202-791, S (+) stereoisomer (SdzS), caused a dose-dependent increase of Ca2+ in both SHR and WKY rats. Intracellular calcium release sites were defined by "hot spots" of high fluorescence intensity ratio in both central and peripheral regions of the sarcoplasm. The size and intensity of hot spots increased, and there was an initial transient activation of subsarcolemmal calcium pools in response to high K+ with 1 microM Ca2+ agonist. In contrast, treatment of the cells with the R (-) stereoisomer of Sdz 202-791 (SdzR), a Ca2+ antagonist, prevented the increase in Ca2+ and the increase in hot spot size by either K+ alone or with agonist. Antagonist decreased central core Ca2+ release and fragmented the subsarcolemmal hot spots.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Calcium channel alterations in genetic hypertension.

We proposed earlier that voltage-dependent calcium (Ca2+) current is altered in single azygos venous cells from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). In this study, the effects of different intracellular concentrations of ethylene glycol-bis-N,N,N',N',-tetraacetic acid (EGTA) on Ca2+ currents were investigated. Vascular muscle cells from SHR and WKY rats were equilibrated with pipette solution containing 0.1 mM or 10 mM EGTA. Increasing the EGTA concentration from 0.1 to 10 mM in SHR vascular cells significantly enhanced the peak amplitude of the longer lasting (L) current from 87 +/- 12 pA to 152 +/- 8 pA, while the transient (T) current amplitude was not significantly different (52 +/- 7 pA and 36 +/- 7 pA, respectively). In WKY rat vascular muscle cells, the amplitudes of the T and L currents were not significantly different with the same comparison of intracellular EGTA concentrations. These observations suggest that relatively low intracellular Ca2+ concentrations can more strongly modulate Ca2+ current through the L channel in SHR than WKY rat vascular muscle cells.

Animals↗
PubMed1989

Relaxation of rat vascular muscle by peripheral benzodiazepine modulators.

Effects of peripheral benzodiazepine receptor modulating drugs, Ro 5-4864 and PK 11195, on tension induced by K+ and the calcium agonist SDZ 202 791 (S isomer), were studied in rat caudal arteries. A significant reduction of tonic phase tension occurred with 30 nM PK 11195 or 3 microM Ro 5-4864, but decreases of the initial (first 3 min), phasic contraction were detected only at the highest concentrations of Ro 5-4864 and PK 11195. Protoporphyrin IX, the putative endogenous ligand of the peripheral benzodiazepine receptor, (at 10-100 nM) markedly increased the effectiveness of Ro 5-4864 and PK 11195 in reducing phasic contraction. Intracellular calcium localization and distribution in fura-2 loaded single vascular cells were quantitated using a high sensitivity, two-stage microchannel plate, photon-counting (PMI-VIM) camera. Peripheral benzodiazepines reduced intracellular calcium release from centrally located calcium pools, and this decrease of calcium release was potentiated by protoporphyrin IX. The decrease in intracellular calcium activity, which was more pronounced in the central regions where sarcoplasmic reticular elements are numerous, was probably the major mechanism of these vasodilator properties. Measurements of soluble guanylate cyclase activity also supported the intracellular Ca2+ release mechanism. Under conditions where protoporphyrin IX did not significantly stimulate guanylate cyclase, Ro 5-4864 alone or more effectively in combination with protoporphyrin IX stimulated cGMP production and caused relaxation. Guanylate cyclase forms a possible target for these benzodiazepine modulators, a hypothesis that merits further investigation.

Animals↗
PubMed1989

Vascular muscle calcium channel modulation in hypertension.

Indications of membrane alterations in vascular muscle cells of spontaneously hypertensive rats (SHR), compared to their Kyoto-Wistar normotensive controls (WKY), have led to further investigation of calcium channels. Previous work from this laboratory had shown the increased probability for opening of the longer-lasting (L-type) calcium channels in SHR, suggesting differences in number or modulation. These experiments have been carried out on the azygos vein of neonatal rats because that preparation has been characterized electro-physiologically, pharmacologically, and by contractile parameters. Divalent (inward) ion currents through the L-type calcium channels are more readily carried by barium than by calcium, a characteristic that is not true for the transient (T) channels. Because there is an increased ratio of L to T calcium channels in SHR, the substitution of barium for calcium is more apparent for inward current amplitude in SHR than in WKY. This increase in the sustained L-type calcium currents, appearing without increased blood pressure on the venous side in newborn animals, is suggestive of a genetic membrane alteration that could contribute to vascular muscle membrane changes important in the development of increased blood pressure. Description and differentiation of the ribbon shaped vascular muscle cells from cardiac muscle cells, and the potential for confusion of the two in older animals, was addressed. The predominance of T-type calcium currents in these azygos vein cells, which is likely to correlate with the predominance of rapid spontaneous contractions, offers a compelling reason for selection of azygos veins in Ca2+ channel comparisons to establish etiologic factors at the cell level in hypertension.

Animals↗
PubMed1988

Desensitization to norepinephrine includes refractoriness of calcium release in myocardial cells.

Localization of myoplasmic free calcium was measured in fura2-loaded single rat myocardial cells to determine whether the mechanism of norepinephrine desensitization includes redistribution of calcium. Fluorescence intensities at each pixel were quantitated by use of a photon-counting, microchannel plate camera. From these images, values of calcium-dependent fluorescence intensity averages in whole cells, areas of calcium release (as zones of high intracellular calcium concentrations), and ratios of fluorescence intensity in central vs. peripheral sites were determined. Stimulation by 1 nM norepinephrine caused an increase in total free intracellular calcium and an activation of intracellular calcium release sites from subsarcolemmal pools initially and later from centrally located calcium pools. Subsequent addition of 100 nM norepinephrine failed to cause significant intracellular calcium release from centrally located pools. In contrast, forskolin exposure still released high concentrations of calcium from these central pools. These results indicate that pretreatment with even a relatively small concentration of norepinephrine causes markedly decreased subsequent intracellular calcium release from centrally located sarcoplasmic reticulum because of a refractoriness of the link between receptor activation and calcium release.

Animals↗
PubMed1988

Cellular calcium control in hypertension.

Membrane mechanisms that are rudimentary to excitation that causes contraction were found to be altered in isolated, single vascular muscle cells of spontaneously hypertensive rats (SHR) compared to normotensive Wistar-Kyoto (WKY) controls. Even in veins of newborn rats, Ca2+ channel proportions are altered to increase the fractional sustained Ca2+ current, providing more Ca2+ that ultimately signals contractile activation. The increase in Ca2+ in SHR could be visualized as a local buildup just inside the cell membrane, suggesting that the process of uptake and removal of Ca2+ at the periphery of the cell may be insufficient to regulate the increased Ca2+ entry. Ca2+ control alterations by subcellular membranes are of sufficient importance to merit consideration as a primary cause of increased peripheral resistance in SHR.

Animals↗
PubMed1988

Calcium currents are altered in the vascular muscle cell membrane of spontaneously hypertensive rats.

Calcium currents were recorded during whole-cell voltage clamp in cultured azygos venous muscle cells from 1-3-day-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Different holding potentials were used to separate total cell current into its transient (T) and sustained or long-lasting (L) components. In recordings from 30 WKY and 30 SHR vascular cells, total cell calcium current was the same between cells from normotensive (167 +/- 20 pA) and hypertensive (139 +/- 15 pA) rats. However, the relative proportion of T and L calcium currents was different between WKY and SHR cells. In WKY cells, the peak amplitude of the L current was less than that of the T current (42 +/- 30% of total current), whereas in SHR cells, the L current was greater (62 +/- 3% of total current). Calcium currents in vascular muscle cells from SHR were activated and inactivated at more positive potentials than in cells from WKY. This study directly compares transmembrane calcium current in isolated cells from WKY and SHR blood vessels and shows that the proportions of T and L calcium channels activated by depolarization are altered in this genetic model of hypertension.

Animals↗
PubMed1988

Ion channel effects of pinacidil in vascular muscle.

Cellular investigation of the vasodilator, pinacidil, was carried out to determine the membrane mechanisms leading to vascular muscle relaxation. Patch clamp recording of whole cell currents from isolated vascular muscle cells of rat azygos vein demonstrated a significant increase in K+ currents when 1 to 50 mumol/L pinacidil was added. The increases of K+ current by pinacidil were small (number of openings increased by 2%) when the recording pipette (and intracellular solution) contained 10 mmol/L EGTA, but were relatively large (50-300% increase in number of openings) when calcium in the intracellular solution was greater than 300 mumol/L. These observations suggest that pinacidil causes vasodilatation by increasing potassium conductance, primarily or completely via the large (200pS), calcium-dependent K+ channel.

Animals↗
PubMed1988

Nitrendipine inhibition of calcium current in rat vascular muscle cells.

The effect of nitrendipine on spontaneous contraction frequency and Ca2+ currents was studied in spontaneously active rat azygos venous cells in primary culture. Nitrendipine reduced the frequency of contraction in a concentration-dependent manner, with 50% inhibition (IC50) at approximately 10(-7) M. In similar cells using the whole-cell voltage-clamp technique, nitrendipine (10(-7) M) reduced the peak magnitude of the longer lasting, high-threshold (L) Ca2+ channel current by 52 +/- 6%, while the transient, low-threshold (T) Ca2+ channel current was unaffected. As estimated from the current-voltage inactivation relationship, the dissociation constant (Kd) for nitrendipine binding to the resting state of Ca2+ channels was 108 nM for the L channel and greater than 2 microM for the T channel. This high-affinity binding of the dihydropyridine to the resting state of the L channel in vascular muscle contrasts with the lower-affinity binding reported in cardiac muscle. Thus, nitrendipine may inhibit spontaneous activity in vascular muscle cells at least partly by blocking Ca2+ current through L channels.

Animals↗