bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of cytosolic free calcium concentration in isolated rat ventricular myocytes with quin 2.
Authors: Sheu S S , Sharma V K , Banerjee S P
Published: June 2012

Cytosolic free calcium concentration was determined in isolated ventricular myocytes from adult rats with the calcium-sensitive indicator, quin 2. The fluorescence signal from resting cells indicated that cytosolic free calcium concentration was 181 +/- 18 nM (mean +/- SEM, n = 18). Inhibition of the sodium-potassium pump with strophanthidin (0.1 mM) resulted in an increase of cytosolic free calcium concentration from 186 +/- 17 to 736 +/- 129 nM (n = 6). The results indicate that it is possible to measure cytosolic free calcium concentration in cardiac muscle cells that have been isolated enzymatically. Moreover, they confirm the observation that inhibition of the sodium-potassium pump increases cytosolic free calcium concentration, presumably via the sodium-calcium exchange mechanism.
Vascular adrenergic neuroeffector function does not decline in aged rats.
Authors: Duckles S P , Carter B J , Williams C L
Published: June 2012

To investigate adrenergic control of blood vessels during aging, rats aged 6, 12, 20, and 27 months were studied using in vitro techniques. Accumulation of [3H]norepinephrine, one index of adrenergic nerve density, did not alter with age in the femoral or renal arteries or renal vein. In the femoral vein [3H]norepinephrine accumulation was greater at 6 and 27 months of age. Norepinephrine sensitivity was determined in both an innervated vessel, the femoral artery, and a non-innervated vessel, the carotid artery. In both cases, sensitivity to norepinephrine did not alter with age. In the renal and femoral arteries and veins, no significant changes in maximum responses to norepinephrine (10(-5) M), potassium chloride, or transmural nerve stimulation were seen with advancing age. Furthermore, frequency response curves (2-16 Hz, 200 pulses) did not differ with age for any of the four vessels studied, with one exception. The response to stimulation at 4 Hz of the femoral vein from 6-month-old rats was significantly larger than responses at other ages. During nerve stimulation, the renal vein exhibited rapid contractions superimposed upon the maintained contractile response. This type of rapid contraction occurred only rarely (1 out of 5) in the renal vein from 27-month-old rats. In summary, neither adrenergic nerve density as reflected by [3H]norepinephrine accumulation nor norepinephrine sensitivity decline with age. As the net effect of various components, the ability of vascular smooth muscle to respond to adrenergic nerve stimulation is also maintained during advancing age.
Mechanism of action of angiotensin II and bradykinin on prostaglandin synthesis and vascular tone in the isolated rat kidney. Effect of Ca++ antagonists and calmodulin inhibitors.
Authors: Cooper C L , Shaffer J E , Malik K U
Published: June 2012

We have studied the effect of angiotensin II and bradykinin on prostaglandin output and vascular tone during extracellular calcium depletion and administration of calcium antagonists and calmodulin inhibitors to elucidate the mechanism of action in the isolated rat kidney perfused with Tyrode's solution. Administration of angiotensin II (0.028-0.28 nmol) or bradykinin (0.28-2.8 nmol) enhanced the output of prostaglandin E2 and 6-keto-prostaglandin F1 alpha in a dose-dependent manner. Angiotensin II, but not bradykinin, produced renal vasoconstriction. Omission of calcium from the medium or infusion of calcium entry blockers, diltiazem (60 microM), or nimodipine (47 microM), failed to alter prostaglandin output elicited by angiotensin II or bradykinin; however, the effect of angiotensin II to produce renal vasoconstriction was inhibited. If calcium was omitted from the medium, the intracellular calcium antagonists, 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (23 microM), dantrolene sodium (31 microM), or ryanodine (2 microM), attenuated prostaglandin output caused by angiotensin II but not bradykinin. Calmodulin inhibitors, trifluoperazine (2 microM), napthalene sulfonamide hydrochloride (2 microM), or calmidazolium (2 microM), diminished prostaglandin output elicited by angiotensin II, but not that caused by bradykinin. Trifluoperazine, but not naphthalene sulfonamide or calmidazolium, attenuated the renal vasoconstrictor effect of angiotensin II. Prostaglandin output induced by angiotensin II and bradykinin were inhibited by mepacrine and indomethacin, whereas, the prostaglandin output caused by exogenous arachidonic acid (33 nmol) was abolished by indomethacin but was unaltered by mepacrine, calcium antagonists, and calmodulin inhibitors. From these data, we conclude that angiotensin II produces renal vasoconstriction by a mechanism dependent on extracellular calcium but not calmodulin, whereas angiotensin II-induced prostaglandin output depends on intracellular calcium and calmodulin. In contrast, bradykinin appears to stimulate prostaglandin synthesis by a calcium/calmodulin-independent mechanism.
Neurogenic muscarinic vasodilation in the cat. An example of endothelial cell-independent cholinergic relaxation.
Authors: Brayden J E , Bevan J A
Published: June 2012

Nerve-mediated and acetylcholine-induced dilator behavior of feline posterior auricular arteries was studied in vitro. We evaluated the muscarinic nature and endothelial cell-dependence of the vasodilations and attempted to determine if there are inhibitory muscarinic receptors located directly on the smooth muscle cells in this artery. Transmural nerve stimulation of arteries which were pretreated with guanethidine (5 X 10(-6)M) and constricted with prostaglandin F2 alpha (3 X 10(-6)M) caused a frequency-dependent, tetrodotoxin-sensitive relaxation of up to 50% of induced tone. Atropine (10(-7)M) blocked more than 95% of this response at all frequencies. Removal of the endothelium by rubbing the intimal surface did not affect the magnitude of the response, but prolonged it slightly. Neurogenic relaxations in rubbed preparations were atropine-sensitive, although less so than control at higher stimulation frequencies. Relaxation of this artery to the calcium ionophore A23187 was completely endothelial cell-dependent. However, exogenous acetylcholine caused dose-dependent relaxations both in control and rubbed preparations. We conclude that the posterior auricular artery is an example of a blood vessel which has muscarinic receptors located directly on its smooth muscle cells which, when activated by acetylcholine released from perivascular nerves, mediate a smooth muscle cell relaxation. This finding contrasts with models of the vascular smooth muscle cell which indicates an excitatory role for muscarinic receptors.
Protection of canine cardiac mitochondrial function by verapamil-cardioplegia during ischemic arrest.
Authors: Yoon S B , McMillin-Wood J B , Michael L H , Lewis R M , Entman M L
Published: June 2012

Hemodynamic and mitochondrial function recover following 60 minutes of ischemic arrest and reperfusion in hearts pretreated with verapamil. The present study was carried out to determine whether verapamil prevents the onset of mitochondrial oxidative impairment after 60 minutes of ischemic arrest without reperfusion. Two preparations of mitochondria isolated following Polytron homogenization and subsequent treatment of the myofibrillar pellet with Nagarse were examined for phosphorylating respiration. The Polytron mitochondria were more sensitive to ischemic arrest than were the Nagarse mitochondria with either glutamate-malate (57% vs. 22% inhibition), succinate (+ rotenone) (41% vs. 14% inhibition), or palmitoylcarnitine (57% vs. 27% inhibition) as respiratory substrates. Verapamil pretreatment significantly increased oxidation of all substrates by the subsequently isolated Polytron mitochondria, but only succinate-supported respiration returned to control levels. In contrast, the small amount of respiratory inhibition exhibited by the Nagarse mitochondria after ischemic arrest was insensitive to verapamil pretreatment. We conclude that the Polytron preparation of mitochondria is more susceptible to ischemia than the Nagarse mitochondria, and this susceptibility correlates with a striking sensitivity to verapamil protection. In general, oxidation of NADH-linked substrates, including palmitoylcarnitine, is more affected by ischemic arrest than succinate, and only oxidation of the latter substrate is totally protected by verapamil. The beneficial action of verapamil on mitochondrial function occurs prior to reperfusion. The data suggest that alterations in calcium homeostasis occur during the ischemic period, as well as in the subsequent reperfusion period.
"Fade" of hyperpolarizing responses to vagal stimulation at the sinoatrial and atrioventricular nodes of the rabbit heart.
Authors: Salata J J , Jalife J
Published: June 2012

Previous studies have suggested that maintained vagal stimulation or acetylcholine infusion results in a fade of responses in the sinoatrial node but not in the atrioventricular node, implying different muscarinic receptor subtypes in the two regions. We investigated this hypothesis in 23 isolated rabbit atrial preparations made quiescent by continuous superfusion with verapamil (1 microgram/ml). Transmembrane potentials were recorded simultaneously from cells in the sinoatrial pacemaker region and from the "N" region of the atrioventricular node. Postganglionic vagal stimulation was achieved by the application of trains of pulses (50-150 microseconds; 10-20 V; 200 Hz). Simultaneous application of long-lasting (1-10 sec) vagal trains produced hyperpolarizations which were nearly identical for both nodal regions. Maximal hyperpolarizations (approximately or equal to 24 mV for sinoatrial node; 26 mV for atrioventricular node) were reached about 500 msec after initiation of the vagal train. Thereafter, hyperpolarizations faded, following a biphasic time course, and thus displaying two different time constants, one fast (tau fast = 580 msec for sinoatrial node; 550 msec for atrioventricular node), and one slow (tau slow = 9.2 sec for both sinoatrial and atrioventricular nodes). Hyperpolarizations during brief (200-msec) but repetitive vagal trains also faded biphasically, but approached a steady state much more rapidly than responses to long-lasting trains. Recovery from hyperpolarization decay occurred rather slowly and was linear. Our results demonstrate that the membrane potential responses to vagal stimulation in the atrioventricular node are indistinguishable from those in the sinoatrial node, and suggest that similar muscarinic receptors are operative in both regions. These phenomena may play an important role in the response of the cardiac conducting system to direct or reflexly mediated vagal input.
Effects of propranolol on atherogenesis in the cholesterol-fed rabbit.
Authors: Chobanian A V , Brecher P , Chan C
Published: June 2012

These studies have examined the effects of dl-propranolol, d-propranolol, and metoprolol on aortic atherogenesis in the cholesterol-fed rabbit and have correlated the vascular effects of the drugs with their influence on blood pressure, plasma lipids and lipoproteins, arterial metabolism, and arterial permeability. dl-Propranolol, and, to a lesser extent, d-propranolol, used in clinically relevant doses of 5 mg/kg body weight per day, inhibited the development of aortic atherosclerosis in association with significant reductions in aortic free and esterified cholesterol content. No significant effects of the drugs on blood pressure or on the total amounts or types of circulating lipoproteins were apparent. Accumulation of cholesterol in the liver and adrenal gland was not influenced by propranolol. Aortic acyl CoA:cholesterol acyltransferase and lysosomal enzyme activities were reduced by propranolol administration, but the inhibition may have been secondary to the lesser degrees of atherosclerosis and cholesterol accumulation present. In vitro inhibition of acyl CoA:cholesterol acyltransferase activity by either dl- or d-propranolol was also observed, but occurred only at propranolol concentrations of 10(-3) M or greater. Treatment with dl-propranolol had no significant effect on the rate of transport of labeled albumin across the isolated carotid artery of cholesterol-fed rabbits. Metoprolol administration (6.25 mg/kg body weight per day) had no significant influence on atherogenesis or arterial metabolism in this model. The results suggest that propranolol inhibits in part the development of atherosclerosis in the cholesterol-fed rabbit, and that the effect may be related to a direct action on the arterial wall.
Differences in norepinephrine activation and diltiazem inhibition of calcium channels in isolated rabbit aorta and mesenteric resistance vessels.
Authors: Cauvin C , Lukeman S , Cameron J , Hwang O , van Breemen C
Published: June 2012

The mechanisms of norepinephrine stimulation of calcium ion entry in isolated rabbit aorta and mesenteric resistance vessels were studied through measurements of effects on calcium-45 influx, tension, and membrane potential. The resistance vessels were considerably less sensitive to norepinephrine than the aorta. The aorta exhibited complex dose-response curves for norepinephrine-stimulated calcium influx and contraction, whereas these were simple in the arterioles. Both vessels were depolarized with increasing concentrations of potassium. Norepinephrine did not depolarize the aorta, whereas it did depolarize the mesenteric resistance vessels. This result supports the contention that norepinephrine opens receptor-operated channels to induce calcium entry in the aorta, while it may activate potential sensitive calcium channels in the mesenteric resistance vessels. However, the maximum depolarization with norepinephrine (10(-4) M) in the arterioles was completely blocked by 10(-5) M diltiazem, whereas that induced by 80 mM potassium was unaltered by the diltiazem. Furthermore, 10(-4) M norepinephrine was able to stimulate virtually the same contraction and calcium influx in 80 mM potassium-depolarized arterioles as in normal polarized tissues. These results are consistent with norepinephrine opening of receptor-operated channels to allow calcium entry in the rabbit mesenteric resistance vessels. That the behavior of norepinephrine-activated channels in the aorta is more complex than in the arterioles is further illustrated by a dramatically decreasing sensitivity of norepinephrine-stimulated calcium influx to diltiazem with increasing norepinephrine in the aorta but not in the arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)
Nafazatrom-induced salvage of ischemic myocardium in anesthetized dogs is mediated through inhibition of neutrophil function.
Authors: Bednar M , Smith B , Pinto A , Mullane K M
Published: June 2012

The effects of nafazatrom on leukocyte function in vitro and in vivo were related to its ability to salvage ischemic myocardium in an occlusion-reperfusion model of myocardial injury in the anesthetized dog. Nafazatrom (0.4-75 microM) produced dose-related inhibition in vitro of neutrophil aggregation, superoxide anion generation, arachidonic acid metabolism, and, to a lesser extent, the release of beta-glucuronidase. In contrast, nafazatrom (0.4-37.5 microM) did not substantially influence platelet aggregation or the platelet metabolism of arachidonic acid. In vivo nafazatrom (10 mg/kg, po) reduced infarct size from 58 +/- 3% of the risk area (mean +/- SEM, n = 9) in control dogs to 23 +/- 2% of the risk area (n = 9, P less than 0.01). Nafazatrom also reduced the incidence of accompanying arrhythmias. Nafazatrom-induced myocardial salvage was not associated with any hemodynamic changes; moreover, it was independent of platelets, since thrombocytopenia did not prevent nafazatrom from exerting a protective effect. Measurements of the neutrophil-specific myeloperoxidase enzyme in ischemic myocardium indicate that the smaller infarct size in dogs treated with nafazatrom is accompanied by diminished leukocyte infiltration. Thus, the ability of nafazatrom to inhibit neutrophil function in vitro and cell infiltration in vivo may underly its myocardial-protective effects.
Effect of sodium-potassium pump inhibitors and membrane-depolarizing agents on sodium nitroprusside-induced relaxation and cyclic guanosine monophosphate accumulation in rat aorta.
Authors: Rapoport R M , Schwartz K , Murad F
Published: June 2012

The purpose of this study was to investigate the relationship between sodium nitroprusside-induced relaxation, inhibition of the sodium-potassium pump, and cyclic guanosine monophosphate. Exposure of rat thoracic aorta to ouabain, or potassium- or magnesium-free Krebs-Ringer bicarbonate solution, procedures which presumably inhibit the sodium-potassium pump, or to potassium chloride or tetraethylammonium, membrane-depolarizing agents, inhibited relaxation to nitroprusside. These conditions had little or no effect on the elevated cyclic guanosine monophosphate levels at a concentration of nitroprusside (0.1 microM) that relaxed norepinephrine contracted tissues by 80%. However, at a maximum relaxant concentration of nitroprusside (1.0 microM), these conditions decreased the elevation of cyclic guanosine monophosphate. The inhibition of elevated cyclic guanosine monophosphate levels was independent of the endothelium, extracellular calcium, and the cyclic guanosine monophosphate phosphodiesterase inhibitor, M&B 22,948. The inhibitory effects of ouabain and of potassium- and magnesium-free solution on the increased levels of cyclic guanosine monophosphate caused by 1.0 microM nitroprusside were abolished when tissues were incubated without norepinephrine, or with norepinephrine in the presence of the alpha-adrenergic blocker, phentolamine. In contrast, a beta-adrenergic blocker, propranolol, had no effect on the ouabain-induced inhibition of elevated cyclic guanosine monophosphate levels, with norepinephrine present. These results are consistent with the hypothesis that membrane events regulate cyclic guanosine monophosphate synthesis. At nitroprusside concentrations greater than 0.1 microM, the formation of cyclic guanosine monophosphate appears to be coupled to the status of the smooth muscle cell membrane and integrity of the sodium-potassium pump.(ABSTRACT TRUNCATED AT 250 WORDS)
Renal nerve stimulation causes alpha 1-adrenoceptor-mediated sodium retention but not alpha 2-adrenoceptor antagonism of vasopressin.
Authors: Smyth D D , Umemura S , Pettinger W A
Published: June 2012

Renal alpha 2-adrenoceptor stimulation by epinephrine infusion reverses cyclic adenosine monophosphate-mediated effects of vasopressin on sodium and water excretion. We used this response to determine whether renal nerve stimulation can activate renal alpha 2-adrenoceptors in the non-recirculating isolated perfused rat kidney (Krebs-Henseleit solution; 3.5 g/100 ml Ficoll; 1 g/100 ml albumin; 36 degrees C; propranolol 100 nM). In the presence of alpha 1-adrenoceptor blockade with prazosin (30 nM) alpha 2-adrenoceptor stimulation with epinephrine reversed the cyclic adenosine monophosphate-mediated effects of vasopressin on sodium (P less than 0.05) and water (P less than 0.05) excretion. Subthreshold (for vasoconstriction) renal nerve stimulation (10 V; 1 msec; 0.65 +/- 0.10 Hz) failed to alter the effect of vasopressin. Similarly, higher levels of renal nerve stimulation [plus prazosin (100 nM) or phenoxybenzamine (1.0 mg/kg per hr) to block alpha 1-adrenoceptors] did not activate renal alpha 2-adrenoceptors which are associated with the antagonism of the effects of vasopressin. The same level of subthreshold renal nerve stimulation (0.85 +/- 0.14 Hz) in the absence of vasopressin, and without alpha 1- or alpha 2-adrenoceptor blockade, decreased (P less than 0.05) sodium and water excretion. The reversal of this effect by alpha 1-adrenoceptor blockade (prazosin 30 nM) but not alpha 2-adrenoceptor blockade (yohimbine 300 nM) indicates that this effect of renal nerve stimulation is mediated through alpha 1-adrenoceptors. Thus, subthreshold renal nerve stimulation in the rat kidney induces sodium and water retention through activation of alpha 1-adrenoceptors, as shown by others in the rabbit and dog.(ABSTRACT TRUNCATED AT 250 WORDS)
Leukotriene D4 relaxes canine renal and superior mesenteric arteries.
Authors: Secrest R J , Olsen E J , Chapnick B M
Published: June 2012

To characterize the influences of leukotriene D4 on regional vascular smooth muscle, effects of leukotriene D4 on vasomotor tone of canine renal and superior mesenteric arterial rings were determined. Vascular smooth muscle tone was measured with isometric force transducers. After tone had been induced with norepinephrine, leukotriene D4, in concentrations of 10(-8) M to 10(-7) M, produced dose-dependent relaxation of renal and superior mesenteric arterial rings. Leukotriene D4-induced relaxation was observed only in those ring preparations in which care had been taken to avoid damaging the luminal surface. Acetylcholine (10(-7) M) also decreased tone in these same ring segments. Neither acetylcholine nor leukotriene D4 altered tone of arterial rings after the endothelium had been intentionally disrupted by rubbing with a cotton-tipped applicator. Nitroglycerin (10(-6) M) relaxed rings both before and after rubbing the intimal surface. These results demonstrate that leukotriene D4 possesses the capacity to relax canine superior mesenteric and renal arterial rings in an endothelial-dependent manner. Because relaxation of renal and superior mesenteric arterial rings in response to leukotriene D4 was not altered after incubation with indomethacin (10(-5) M), the observed endothelial-dependent relaxation induced by leukotriene D4 did not appear to be related to release of a cyclooxygenase metabolite(s). In contrast, FPL 55712 (10(-5) M) attenuated the relaxation produced by leukotriene D4, suggesting that this response was a receptor-linked consequence.
Heterogeneity of myosin isozyme content of rabbit heart.
Authors: Litten R Z , Martin B J , Buchthal R H , Nagai R , Low R B , Alpert N R
Published: June 2012

A detailed study was carried out to measure the relative contents of V1 and V3 myosin isozymes in different regions of rabbit ventricle as a function of age, to assess animal-to-animal variability, and to compare different experimental approaches aimed at minimizing the effects of such variability. In addition, comparisons were made in normal developing hearts between ventricular isozyme composition and myofibrillar myosin calcium-stimulated adenosine triphosphatase. V1 isozyme predominated relative to V3 isozyme in the hearts of 2-week-old rabbits, decreasing to become a minor component in 10-week-old animals. Despite this trend, there was considerable variability in relative isozyme content of whole ventricular tissue among different rabbits of the same age. This variability was reduced in comparisons of littermates and by use of cardiac biopsies to measure changes in isozyme content in the same animal over time. Within different regions of a given heart, there also were small but significant differences in the percent V1 isozyme. The percent V1 was greatest for right ventricular papillary, followed by right ventricular free wall and then the left ventricle (free wall plus septum). There also were differences in the percent V1 within those regions, as exemplified by the significantly higher values for ventricular epicardium vs. endocardium. There was a linear correlation between the myofibrillar myosin calcium-stimulated adenosine triphosphatase and percent V1 of total isozyme for both right and left ventricles in normal and developing hearts. The regression lines for calcium-stimulated adenosine triphosphatase vs. percent V1 had a steeper slope in the left than in the right ventricle.
Phorbol ester- and diacylglycerol-mediated desensitization of cardiac beta-adrenergic receptors.
Authors: Limas C J , Limas C
Published: June 2012

There are specific phorbol ester receptors on cardiac myocytes which may be identical with the calcium/phospholipid-dependent protein kinase (protein kinase C). Incubation of enzymatically dissociated rat cardiac myocytes with biologically active phorbol esters (such as 4 beta-phorbol-12, 13-dibutyrate and 12-O-tetradecanoyl phorbol-13-acetate) leads to a time- and concentration-dependent loss of beta-adrenergic receptors detectable with the hydrophilic ligand [3H]-CGP-12177. This loss is attributable to a reduction in both maximal beta-receptor numbers and their affinities. The synthetic diacylglycerol, 1-oleyl-2-acetyldiglycerol, which is known to activate protein kinase C, also induces desensitization of beta-receptors. Both phorbol dibutyrate and 1-oleyl-2-acetyldiglycerol have additive effects to isoproterenol, suggesting a separate site of action in promoting beta-receptor desensitization. The effects of phorbol dibutyrate and 1-oleyl-2-acetyldiglycerol are prevented by colchicine (but not its inactive analog, trimethylcolchicinic acid), indicating a microtubule dependence. The loss of membrane-bound beta-receptors after phorbol dibutyrate- or 1-oleyl-2-acetyldiglycerol preincubation is accompanied by an increase in beta-receptors associated with a cytosol-derived vesicular fraction devoid of plasma membrane markers, a finding consistent with an internalization process. These results suggest that protein kinase C activation by diacylglycerols derived from receptor-linked phosphoinositide hydrolysis may be a novel mechanism of cardiac beta-receptor desensitization.
Alpha 1-adrenergic and muscarinic cholinergic stimulation of phosphoinositide hydrolysis in adult rat cardiomyocytes.
Authors: Brown J H , Buxton I L , Brunton L L
Published: June 2012

Cardiac alpha-adrenergic receptors mediate cellular responses to norepinephrine through an undefined series of molecular events. We examined the possibility that phosphoinositide hydrolysis was stimulated through alpha-adrenergic receptors in cardiomyocytes purified from adult rat ventricle. Phosphoinositide stores were labeled with [3H]inositol, and [3H]inositol phosphate formation was assessed after the addition of lithium chloride and norepinephrine. Norepinephrine increased the accumulation of [3H]inositol phosphate by approximately 5-fold, giving a maximal response at approximately 30 microM and a half-maximal response at approximately 1 microM. There was a significant increase in [3H]inositol phosphate formation in response to norepinephrine at 5 minutes, and the response was linear over 40 minutes. Norepinephrine-stimulated [3H]inositol phosphate formation was not blocked by propranolol (1 microM) or yohimbine (0.1 microM) but was completely antagonized by the alpha 1-selective antagonist prazosin (0.1 microM). Muscarinic cholinergic receptor activation by carbachol also stimulated [3H]inositol phosphate formation in rat ventricular myocytes. The maximal effect of carbachol (approximately 2-fold) was always less than that of norepinephrine. The combined effects of norepinephrine and carbachol were additive, suggesting that the two hormones do not share a common rate-limiting step. Removal of extracellular calcium and addition of ethylene glycol bis(beta-amino ether)-N,N'-tetraacetic acid, attenuated, but did not abolish, norepinephrine- or carbachol-stimulated [3H]inositol phosphate formation. Neither the calcium ionophore A23187 nor the calcium channel blockers verapamil and nifedipine had any effect on basal or hormone-stimulated [3H]inositol phosphate formation. We suggest that some of the physiological and metabolic effects of adrenergic and cholinergic stimulation on the rat myocardium are secondary to receptor-mediated hydrolysis of phosphoinositides.
Local diversity of myosin expression in mammalian atrial muscles. Variations depending on age and thyroid state in the rat and the rabbit.
Authors: Dechesne C A , Léger J , Bouvagnet P , Mairhofer H , Léger J J
Published: June 2012

Rat, rabbit, pig, and bovine atrial myocardia were investigated with anti-alpha and anti-beta myosin heavy chain monoclonal antibodies. Analysis of atrial fibers by indirect immunofluorescence and assay of myosin heavy chains in tissue micro samples by immunoaffinity chromatography revealed both heterogeneity and plasticity in the atrial myosin heavy chains, undetected by electrophoresis of native atrial myosins under nondenaturing conditions. We found both alpha- and beta-like myosin heavy chains to be expressed in rat and rabbit, as they are in pig and bovine, atrial myocardia. They were regionally distributed within atrial muscles. The beta-like myosin heavy chains were present at much lower levels in rat and rabbit atria than in pig and bovine atria. Young rat atrial myosin was composed of only alpha-like heavy chains. In the rat and the rabbit, hyperthyroidism induced a beta- to alpha-like myosin heavy chain transition, which was considerable in the right atria and complete in the left atria. In the rat, thyroidectomy induced a moderate alpha- to beta-like myosin heavy chain transition, visible in the left atria. The significance of this atrial myosin heavy chain polymorphism is discussed in relation to the existence of anatomical localizations of the two myosin variants.
Bovine and human endothelial cell production of neutrophil chemoattractant activity in response to components of the angiotensin system.
Authors: Farber H W , Center D M , Rounds S
Published: June 2012

Although there is growing evidence that angiotensin II affects macrophage-mediated inflammatory responses, it is unclear whether it can affect neutrophil-mediated inflammatory responses. Because vascular endothelial cells are capable of releasing neutrophil chemoattractant activity, we attempted to determine whether components of the angiotensin system could affect neutrophil-mediated responses indirectly by stimulating endothelial cells to release neutrophil chemoattractant substances. Cultured bovine and human endothelial cells incubated with angiotensin II released neutrophil chemoattractant activity. This activity appeared within 1 minute of exposure to angiotensin II, and was blocked by saralasin, an angiotensin II antagonist. Angiotensin I also caused release of neutrophil chemoattractant activity, but its effect required conversion to angiotensin II. Bradykinin, another substrate for angiotensin-converting enzyme, did not stimulate appearance of chemoattractant. Chemoattractant generation was not inhibited by indomethacin but was blocked by diethylcarbamazine and 5,8,11,14-eicosatetraynoic acid. This study demonstrates that angiotensin II may influence neutrophil accumulation, via production of neutrophil chemoattractant activity by vascular endothelial cells.
Release of unassembled rat cardiac myosin light chain 1 following the calcium paradox.
Authors: Samarel A M , Ferguson A G , Vander Heide R S , Davison R , Ganote C E
Published: June 2012

To determine the intracellular source and release kinetics of myosin light chain 1 immediately following irreversible myocytic injury, we perfused rat hearts in a Langendorff apparatus under control conditions (20 minutes), or during global cellular injury produced by oxygenated, calcium-free perfusion (5 minutes), followed by reperfusion with buffer containing 2.5 mM calcium (15 minutes). Light chain 1 concentration (double antibody radioimmunoassay) and creatine kinase activity were measured in both the coronary effluent and the 140,000 g supernatant extract of perfused ventricular tissue (after homogenization and ultracentrifugation). Calcium reperfusion caused the rapid release of both light chain 1 and creatine kinase activity (peak light chain 1 = 1.09 +/- 0.19 micrograms/g; peak creatine kinase = 74.9 +/- 10.7 IU/ g at 1 minute, mean +/- SD, n = 3); 28.5 +/- 13.5% of total light chain 1 and 86.5 +/- 0.6% of total creatine kinase activity were depleted from the tissue extract during the 15-minute reperfusion. No light chain 1 or creatine kinase was detected in the effluents of control-perfused hearts. Dodecyl sulfate polyacrylamide gel electrophoresis and immunodetection with specific antibody to myosin heavy chain and light chain 1 showed that the effluent light chain 1 was of similar molecular weight (mol wt = 27,000) to the subunit bound to myofibrils. In addition, light chain 1 was released in the absence of myosin heavy chain. Thus, a small soluble pool of unassembled myosin light chain 1 subunits exists in the cytoplasm of cardiac myocytes that is released from irreversibly injured cells. This pool demonstrates initial washout kinetics similar to creatine kinase.
Adrenergic regulation of myosin adenosine triphosphatase activity.
Authors: Winegrad S , Weisberg A , Lin L E , McClellan G
Published: June 2012

The amount of inorganic phosphate liberated by the adenosine triphosphatase activity of myosin in a thin section of cardiac tissue can be measured quantitatively by precipitation with calcium in an alkaline medium under a defined set of conditions. Specificity of the procedure for myosin adenosine triphosphatase has been confirmed by the response to inhibitors and to different degrees of contractile filament overlap. Precise quantitation of adenosine triphosphatase activity has been demonstrated by (1) constant rate over time, (2) linearity with amount of enzyme, (3) correct values for the Km of adenosine triphosphate, and (4) a similar value for Vmax to those determined by more traditional procedures. Stimulation of the beta-adrenergic system by the release of catecholamines following injection of the animal with 6-hydroxydopamine causes a rise and then a fall of both calcium- and actin-activated adenosine triphosphatase in parallel with the changes in blood levels of the transmitter. Tyramine injection of rats produces a dose related increase in myosin adenosine triphosphatase. Perfusion of isolated hearts with isoproterenol increases myosin adenosine triphosphatase in dose-related manner. Addition of cyclic adenosine monophosphate and phosphodiesterase inhibitor to the solution bathing frozen, dried sections of heart increases both calcium- and actin-activated adenosine triphosphatase activity by almost 150%. The data show that the beta-adrenergic system, through cyclic adenosine monophosphatate, regulates the enzymatic activity of myosin, independent of the concentration of calcium. The possible role of this regulatory mechanism in the physiological modulation of cardiac contractility is discussed.
Replication of smooth muscle cells in vascular disease.
Authors: Schwartz S M , Campbell G R , Campbell J H
Published: June 2012

Smooth muscle proliferation has been recognized as central to the pathology of both major forms of vascular disease: atherosclerosis and hypertension. Recent advances in our knowledge of mechanisms of control of proliferation suggest that events occurring in adult animals may recapitulate portions of the developmental biology of the smooth muscle cell. This review attempts to consider the current state of knowledge of the mechanisms controlling smooth muscle proliferation in these two diseases, to put that knowledge into the context of what is known about smooth muscle biology, and to offer two hypotheses on the possible roles of smooth muscle developmental biology in manifestations of atherosclerosis and hypertension in adult humans.
A possible role for endogenous prostaglandins in the electrophysiological effects of acetylstrophanthidin on isolated canine ventricular tissues.
Authors: Moffat M P , Ferrier G R , Karmazyn M
Published: June 2012

A possible role for endogenous prostaglandins in the toxic electrophysiological effects of the aglycone acetylstrophanthidin was studied in isolated canine Purkinje fiber papillary muscle preparations by standard microelectrode techniques. Acetylstrophanthidin (5 X 10(-8) g/ml) caused a significant increase in 6-keto-prostaglandin F1 alpha release from these preparations. A significant loss of membrane potential and the development of oscillatory afterpotentials was observed, as well. Administration of either of two nonsteroidal antiinflammatory agents, indomethacin (3 X 10(-5) g/ml) or aspirin (5 X 10(-5) g/ml), in the presence of acetylstrophanthidin, abolished the stimulation of 6-keto-prostaglandin F1 alpha release and delayed and attenuated the loss of membrane potential and the development of oscillatory afterpotentials. In addition, indomethacin and aspirin appeared to preserve the electrogenic pumping capacity of Purkinje fiber cells exposed to acetylstrophanthidin. Exposure of Purkinje tissues to acetylstrophanthidin inhibited post-pacing hyperpolarization normally exhibited by these tissues. Both indomethacin and aspirin decreased this inhibition. Addition of prostacyclin (1 ng/ml) after 30 minutes of exposure to acetylstrophanthidin to preparations in which endogenous prostaglandin synthesis had been inhibited, resulted in a significant increase in the amplitude of oscillatory afterpotentials within 2 minutes. These results suggest that the presence of endogenous prostaglandins may play a role in the development of the toxic electrophysiological effects associated with acetylstrophanthidin.
Stimulation of pulmonary vagal afferent C-fibers by lung edema in dogs.
Authors: Roberts A M , Bhattacharya J , Schultz H D , Coleridge H M , Coleridge J C
Published: June 2012

In anesthetized, open-chest dogs we examined the effect of pulmonary edema on the firing frequency of afferent vagal fibers arising from the lung. We recorded impulses from slips of the cervical vagus nerves and infused isotonic Krebs-Henseleit solution (20% of body weight) intravenously to increase net filtration pressure in the lung microvasculature. Measurement of extravascular lung water (6.0 +/- 0.4 g/g dry lung), and morphological examination of lung tissue (revealing various degrees of perivascular and peribronchial cuffing) confirmed that edema was present. At the end of the infusion when the lungs were congested (lung microvascular pressure, 37 cm water) and edematous, the impulse frequency of pulmonary and bronchial C-fibers and rapidly adapting receptors had increased 5-6 times. The only significant change in slowly adapting receptor activity was an increase during deflation. When lung water was still elevated but lung microvascular pressure had been restored to control by withdrawal of blood, impulse activity of rapidly and slowly adapting receptors reverted to or below control. Pulmonary C-fiber activity, although less than during congestion, remained significantly above control, several C-fibers being stimulated by interstitial edema in the absence of alveolar edema. Bronchial C-fibers were stimulated in severely edematous lung showing pronounced peribronchial cuffing and alveolar edema, but were not stimulated in milder grades of edema. Our results support the hypothesis (Paintal, 1969) that pulmonary C-fibers (J-receptors) are stimulated by an increase in interstitial pressure secondary to edema.
Cumulative depletions of extracellular calcium in rabbit ventricular muscle monitored with calcium-selective microelectrodes.
Authors: Bers D M , MacLeod K T
Published: June 2012

Transient changes of extracellular free calcium in rabbit ventricular muscle under nonsteady state conditions were measured with double-barreled calcium microelectrodes. Resumption of stimulation after a rest interval produces a cumulative decrease of extracellular free calcium often by more than 10% (with bulk extracellular free calcium = 0.2 mM). The extracellular free calcium returns to the bulk value as a new steady state is achieved. The changes of extracellular free calcium recorded presumably represent net calcium uptake and loss by cardiac muscle cells. These cumulative extracellular free calcium depletions are blocked by 0.5 mM cobalt and 1 microM nifedipine and are increased to 167 +/- 11% of control by the calcium agonist Bay k 8644 (1 microM) and to 620 +/- 150% of control by increasing stimulus frequency from 0.2-2 Hz. Caffeine (10 mM) inhibits the cumulative extracellular free calcium depletions, probably by rendering the sarcoplasmic reticulum unable to accumulate calcium. It is proposed that the extracellular free calcium depletions recorded represent, in large part, calcium which has entered the cells and has been taken up by the sarcoplasmic reticulum (which had become depleted of calcium during the rest interval). Nifedipine and cobalt inhibit these cumulative depletions presumably by preventing the calcium entry which could subsequently be accumulated by the sarcoplasmic reticulum. The net cellular calcium uptake produced by such a post-rest stimulation protocol can also be inhibited by 1-3 microM acetylstrophanthidin and reduction of extracellular sodium to 70 mM. Acetylstrophanthidin and low extracellular sodium would be expected to shift the sodium-calcium exchange in favor of increased calcium uptake, which may, in turn, prevent the loss of sarcoplasmic reticulum calcium during the rest interval. This would limit the amount of calcium which the sarcoplasmic reticulum could take up with subsequent activation. In contrast to the results with caffeine, ryanodine (1 microM) increases the magnitude and rate of calcium uptake after a rest interval, indicative of a fundamental difference in the actions of caffeine and ryanodine. When stimulation is stopped in the presence of ryanodine, extracellular free calcium increases much faster than in control. This suggests that ryanodine may enhance calcium uptake by the sarcoplasmic reticulum during repetitive stimulation and may enhance calcium efflux from the sarcoplasmic reticulum during quiescence. These experiments provide insight into transsarcolemmal calcium movements and certain aspects of cellular calcium regulation.
Calcium-sensitive cellular and subcellular transport of sodium, potassium, magnesium, and calcium in sodium-loaded vascular smooth muscle. Electron probe analysis.
Authors: Wasserman A J , McClellan G , Somlyo A P
Published: June 2012

Electron probe x-ray microanalysis of the composition of rabbit portal anterior mesenteric vein smooth muscle was performed following sodium loading and washout into sodium-free lithium solutions. Sodium and lithium were also measured with atomic absorption spectrophotometry. Cellular uptake of sodium and loss of potassium during sodium loading were much faster at high (37 degrees C) than at low (2 degrees C) temperature, as was the passive ouabain-resistant uptake of potassium during lithium washout. The loss of sodium at 2 degrees C into lithium solution consisted of two components: a rapid efflux that was complete by 30 minutes, and a slow component that required at least 24 hours for completion. The amount of sodium lost through the first component (approximately 200-300 mmol/kg dry weight) was relatively independent of the amount of sodium loading. The loss of cellular sodium at 2 degrees C, after 30 minutes, was accompanied by a gain of cellular lithium. Ouabain-resistant sodium loss and lithium and potassium uptake were markedly accelerated at 37 degrees C; sodium loss was complete (1200 mmol sodium/kg dry weight lost) by 30 minutes of washout. Sodium-loaded cells also lost chloride ion and gained magnesium during sodium efflux at 37 degrees C. Mitochondrial and nuclear sodium and potassium were correlated with the respective cytoplasmic concentrations during both sodium loading and sodium washout, indicating the relatively rapid equilibration of the monovalent ions between the cytoplasm and organelles. Calcium-free solutions markedly inhibited the ouabain-resistant sodium and chloride ion effluxes and potassium influx in muscles incubated, after sodium loading, in lithium solutions at 37 degrees C. These fluxes could be restored to near normal values by 0.2 mM calcium. The calcium sensitivity of the ouabain-resistant sodium, potassium, and chloride ion fluxes observed in this and other studies raises the possibility that some abnormalities of monovalent ion transport observed in cells of hypertensives are secondary to changes in cellular calcium.
Decreased basal cardiac interstitial norepinephrine release after neuronal uptake inhibition in dogs.
Authors: Cousineau D , Goresky C A , Rose C P
Published: June 2012

The effect of neuronal uptake inhibition on basal interstitial release of norepinephrine in the canine heart was examined by use of the multiple tracer dilution-bulk balance technique. A kinetic model incorporating the effects of flow, capillary permeability-surface product for norepinephrine, the interstitial uptake rate constant for neurotransmitter, and plasma norepinephrine input and output values was used to estimate rates of uptake from and release of norepinephrine into the interstitial space. The intravenous injection of the neuronal uptake inhibitor desipramine in anesthetized dogs under basal conditions reduced interstitial uptake of tracer norepinephrine in the heart, without significant changes in plasma concentration of norepinephrine in aorta and coronary sinus. The lack of change in the arteriovenous balance for norepinephrine across the heart, in the face of the lowered uptake for this amine, suggested that the liberation of norepinephrine by cardiac sympathetic fibers was reduced. Analysis of the data with the norepinephrine tracer kinetic-bulk model showed that, after desipramine, the interstitial release of norepinephrine was reduced to the same extent as uptake was diminished. As a result, the concentration of norepinephrine in the extracellular space of the heart did not increase significantly. The findings indicate the presence of a presynaptic neuronal feedback inhibition of release, which serves to fine tune the myocardial interstitial concentration of norepinephrine in the basal state; with this, after desipramine, both norepinephrine uptake and release are correspondingly diminished.
Developmental changes in contractile protein adenosine 5'-triphosphatase in the rabbit heart.
Authors: Nakanishi T , Nagae M , Takao A
Published: June 2012

This study was designed to investigate developmental changes in contractile protein adenosine 5'-triphosphatase in the rabbit heart. Myofibrils and myosin were isolated from ventricular muscles from the fetal, newborn, and adult rabbits. Actin and troponin-tropomyosin complex were isolated from the adult skeletal muscle. Myofibrillar (actomyosin) adenosine 5'-triphosphatase measured at low ionic strength increased with development. In contrast, myofibrillar calcium adenosine 5'-triphosphatase at high ionic strength was the greatest in the newborn and the lowest in the adult. Myosin calcium adenosine 5'-triphosphatase and actin-activated myosin adenosine 5'-triphosphatase were also the greatest in the newborn and the lowest in the adult. The relative proportion of myosin isozyme V1 was the greatest in the newborn and the lowest in the adult. The addition of troponin-tropomyosin complex stimulated myosin adenosine 5'-triphosphatase in the presence of calcium in the adult, but not in the newborn and fetus. As a result, actin-activated myosin adenosine 5'-triphosphatase in the presence of troponin-tropomyosin complex was the greatest in the adult, followed by the newborn and fetus. These data suggest that the low myofibrillar adenosine 5'-triphosphatase activity at low ionic strength in the premature heart may be due to the age-related difference in the interaction of myosin with troponin-tropomyosin. Developmental change in myosin calcium adenosine 5'-triphosphatase (which is determined by the relative proportion of isomyosin V1 and V3) may not be directionally identical to that of the physiologically important myofibrillar adenosine 5'-triphosphatase.