bluuebunny/crossref_metadata_2025 huggingface dataset:
Na+/H+ and Na+/Ca2+ exchange in regulation of [Na+]i and [Ca2+]i during metabolic inhibition
Authors: Satoh H. , Hayashi H. , Katoh H. , Terada H. , Kobayashi A.
Published: December 2017

The relationships among intracellular Na+ and Ca2+ concentrations ([Na+]i and [Ca2+]i, respectively) and cell morphology were investigated during metabolic inhibition (MI) in isolated guinea pig myocytes. [Na+]i and [Ca2+]i were measured using the fluorescent indicators, Na(+)-binding benzofuran isophthalate and fluo 3. During the initial 20 min of MI, [Na+]i increased from 6.2 +/- 0.5 to 18.6 +/- 1.6 mM (n = 31), whereas [Ca2+]i, expressed as the percent change of fluo 3 fluorescence, remained at the low level. In the following 30 min, 94% of the cells developed contracture, and [Ca2+]i began to increase after cells had contracted (167 +/- 14% at 50 min). The level of [Ca2+]i during MI was lower than that during 500 microM strophanthidin perfusion. The increase in [Na+]i was not affected by 10 microM tetrodotoxin but was suppressed by 1 microM hexamethylene amiloride (HMA). The application of 10 mM glucose from the start of MI prevented both the increase in [Na+]i and cell contracture. However, the addition of glucose after 20 min of MI [energy repletion (ER)] led to a dramatic increase in [Ca2+]i (442 +/- 72% at 50 min, n = 31), and 84% of the cells developed contracture. The increase in [Ca2+]i and the cell contracture were suppressed by HMA or Ca(2+)-free solution. Intracellular pH decreased from 7.23 +/- 0.07 to 6.95 +/- 0.09 during MI but did not change after ER (6.90 +/- 0.11 at 35 min, n = 9). These findings suggested that during MI 1) [Na+]i increased by both the activated Na+ influx via Na+/H+ exchange and the suppressed Na+ extrusion via the Na+/K+ pump, 2) Na+/Ca2+ exchange was inhibited by energy depletion and intracellular acidosis, and 3) cell contracture was not related to Ca2+ overload but was related to rigor due to energy depletion.
Mitochondrial lipid peroxidation and superoxide dismutase in rat hypertensive target organs
Authors: Ohtsuki T. , Matsumoto M. , Suzuki K. , Taniguchi N. , Kamada T.
Published: December 2017

Mitochondrial respiratory chains leak a large amount of superoxide anion radicals, which chain react with membrane phospholipid to develop lipid peroxidation. Manganese superoxide dismutase (MnSOD) is then inducible and catalyzes superoxide detoxification within mitochondria. We examined mitochondrial thiobarbituric acid-reactive substance, an end product of lipid peroxidation, and MnSOD concentration in hypertensive target organs of spontaneously hypertensive and deoxycorticosterone acetate salts-induced hypertensive rats. Normotensive rats showed significant increases in thiobarbituric acid-reactive substance and MnSOD in the brain as they matured. Mature spontaneously hypertensive and induced hypertensive rats showed a marked elevation of lipid peroxidation but no increase in superoxide dismutase in the brain. The heart and kidney presented no significant difference of lipid peroxidation and superoxide dismutase among strains, ages, and treatments. Abnormal mitochondrial metabolism of oxygen radicals was observed selectively in the brain during hypertension and may contribute to mitochondrial injury and lead to neuronal degeneration or susceptibility to brain ischemia in mature hypertensive rats.
Identification and antisense inhibition of a renin-angiotensin system in transgenic cardiomyocytes
Authors: Cook J. L. , Bhandaru S. , Giardina J. F. , Claycomb W. C. , Re R. N.
Published: December 2017

Cardiac myocytes (AT-1 cells) derived from heart tumors of mice transgenic for an atrial natriuretic factor promoter, SV40 large T-antigen DNA transgene, demonstrate properties consistent with normal cardiac myocytes but retain the capacity to proliferate in culture. We studied the renin-angiotensin system (RAS) and related growth regulation of these cells because AT-1 cells (or transgenically similar cells) may be useful to repair injured myocardium. This study reveals two separate and distinct findings: 1) AT-1 cells proliferate or hypertrophy in response to angiotensin II (ANG II), depending on their competence to proceed through the cell cycle; and 2) AT-1 cells possess components of a RAS, and angiotensinogen antisense experiments suggest that the RAS is functional in these cells. Specifically, AT-1 cells proliferate in response to ANG II in low-serum medium but hypertrophy in response to ANG II when first treated with mitomycin C (at a concentration that inhibits DNA replication but is not cytotoxic). The ANG II-mediated proliferative and hypertrophic responses are inhibited by DuP 753. In addition, there is a significant increase in the protein-to-DNA ratio of cells, which are proliferation-inhibited in the absence of ANG II treatment (20%, P < 0.05). DuP 753 also inhibits this hypertrophy, suggesting that these cells possess a functional RAS. AT-1 cells contain mRNAs for angiotensin-converting enzyme, renin, angiotensinogen, and the AT1 receptor as determined by sequence analysis of polymerase chain reaction amplification products. Antisense oligonucleotides complementary to the angiotensinogen mRNA specifically inhibit angiotensinogen mRNA accumulation and proliferation of AT-1 cells. In summary, these cells contain a growth-regulating RAS, suggesting that such a system may play a significant role in left ventricular hypertrophy.
Protection of reoxygenated cardiomyocytes against hypercontracture by inhibition of Na+/H+ exchange
Authors: Ladilov Y. V. , Siegmund B. , Piper H. M.
Published: December 2017

Effects of Na+/H+ exchange inhibition and cytosolic acidosis on reoxygenated adult rat ventricular cardiomyocytes were investigated. Cells were incubated in anoxic media at pH 6.4 until pCa of < or = 5, intracellular pH (pHi) of 6.5, and cytosolic [Na+] of 50 mM were reached. On reoxygenation, medium pH was changed to 7.4 to activate Na+/H+ exchange. In one group, 20 microM HOE-694, an inhibitor of Na+/H+ exchange, was added. With or without HOE-694, cytosolic Ca2+ and Na+ returned to control levels within 10 min of reoxygenation. In the absence of HOE-694, the pHi renormalized (to 7.2) within 8 min, but irreversible hypercontracture and transient Ca2+ oscillations were observed. In the presence of HOE-694, pHi stayed acidotic (at 6.5), hypercontracture was prevented, and Ca2+ oscillations were attenuated. When the Na+ pump was inhibited with 0.1 mM ouabain, even partial recovery of Ca2+ control became impossible unless HOE-694 was added. Our conclusions are 1) activation of Na+/H+ exchange does not impair recovery of cytosolic Na+ and Ca2+ control unless activity of the sarcolemmal Na+ pump is critically reduced, and 2) due to prolongation of cytosolic acidosis, inhibition of Na+/H+ exchange protects against reoxygenation-induced hypercontracture and cytosolic Ca2+ oscillations.
Overflow of endogenous norepinephrine from PVH nucleus of DOCA-salt hypertensive rats
Authors: Qualy J. M. , Westfall T. C.
Published: December 2017

Previous studies from this laboratory demonstrated that there was enhanced basal and evoked (K+ depolarization) overflow of endogenous norepinephrine (NE) into the perfusate of a push-pull cannula placed in the paraventricular nucleus of the hypothalamus (PVH) of conscious freely moving spontaneously hypertensive rat (SHR) compared with Wistar-Kyoto (WKY) or Sprague-Dawley (SD) rats. The present study was carried out to determine whether results obtained with SHR were specific to this genetic model of hypertension by examining NE release in deoxycorticosterone acetate (DOCA)-salt hypertension. DOCA-salt hypertension was produced in 8-wk-old uninephrectomized SD rats by administering a 50-mg DOCA Silastic pellet subcutaneously 7 days postnephrectomy and providing 0.9% NaCl + 0.2% KCl drinking solution at libitum for 3 wk. Sham-implanted animals received normal tap water. Blood pressure was similar to that of 8- to 10-wk-old SHR. Basal release of NE as well as release after K+ added to the push-pull cannula or sodium nitroprusside or phenylphrine administered intravenously was determined. It was observed that there was no difference in basal overflow or after K+ administration in DOCA-salt hypertensive rats compared with sham animals. Similarly, the increase in NE overflow due to sodium nitroprusside or the decrease due to phenylphrine was similar between DOCA-salt rats or sham controls. This was in sharp contrast to what was observed in SHR: basal or K(+)-evoked release was significantly greater in SHR than WKY, SD, DOCA-salt, or DOCA-sham controls. It is concluded that central noradrenergic activity involving the PVH is not altered in DOCA-salt hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of Hoe-140 and ramiprilat on arteriolar tone and dilation to bradykinin in skeletal muscle of rats
Authors: Koller A. , Rodenburg J. M. , Kaley G.
Published: December 2017

In skeletal muscle of pentobarbital sodium-anesthetized rats, the mechanism of action and possible role of the potent vasodilator bradykinin (BK) in regulation of arteriolar tone were investigated. Changes in diameter of third-order arterioles of cremaster muscle in response to topical administration of BK and other vasoactive agents were measured with an image-shearing monitor and recorded with video microscopy. All agonists were administered topically on the exteriorized muscle. With use of Hoe-140, a B2-receptor antagonist, the presence of kinin receptors in arterioles was studied. In control preparations, 10(-5) M arachidonic acid (AA), 0.5 x 10(-6) M acetylcholine (ACh), and 10(-5) M adenosine (ADO) evoked dilation of arterioles of up to 70% of resting diameter. BK (10(-9), 10(-8), 10(-7), and 10(-6) M) elicited dose-dependent arteriolar dilations (1.3 +/- 1.3, 4.1 +/- 0.5, 10.3 +/- 1.6, and 13.3 +/- 1.3 microns, respectively). In the presence of 10(-7) M Hoe-140, dilations to AA, ACh, and ADO were not affected, but those to 10(-9)-10(-7) M BK were eliminated or significantly inhibited (10(-6) M BK: to 2.9 +/- 1.8 microns). Also, whereas Hoe-140 significantly reduced basal arteriolar diameters (from 16.7 +/- 0.9 to 13.8 +/- 1.1 microns, P < 0.05), it did not affect constrictions to norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential hemodynamic effects of L-NMMA in endotoxemic and normal dogs
Authors: Cobb J. P. , Natanson C. , Quezado Z. M. , Hoffman W. D. , Koev C. A. , Banks S. , Correa R. , Levi R. , Elin R. J. , Hosseini J. M. , et al.
Published: December 2017

We studied the differential hemodynamic effects of N omega-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide (NO) synthesis, in normal and endotoxemic dogs and examined its activity across the venous, pulmonary, and systemic circulations. Survival was used to determine therapeutic efficacy. In both normal and endotoxemic animals, L-NMMA similarly increased systemic (P = 0.01) and pulmonary (P = 0.047) vascular resistance, marginally increased mean arterial pressure (P = 0.07), and decreased oxygen delivery (P = 0.01) compared with normal saline. In contrast, the effect of L-NMMA on mean pulmonary arterial pressure, central venous pressure, and pulmonary capillary wedge pressure was different in endotoxemic than in normal animals (P < 0.05), but this differential effect occurred > 6 h after endotoxin challenge. L-NMMA (1–10 mg.kg-1.h-1) did not significantly increase survival rates or times in endotoxemic animals, but the highest dose decreased survival times (P < 0.05). Thus the effect of L-NMMA was similar on the systemic arterial circulation in endotoxemic dogs compared with normal dogs but was increased in the venous and pulmonary vascular beds after endotoxin, suggesting that the induction of NO production was greater in low-resistance vessels. We were unable to show that nonselective inhibition of NO production was beneficial in endotoxemic dogs.
Pregnancy-induced alterations of neurogenic constriction and dilation of human uterine artery
Authors: Nelson S. H. , Steinsland O. S. , Johnson R. L. , Suresh M. S. , Gifford A. , Ehardt J. S.
Published: December 2017

The responses to electrical field stimulation (EFS) of perivascular nerves in human uterine arteries were characterized. The arteries were removed from pregnant and nonpregnant patients undergoing hysterectomy. Tetrodotoxin, guanethidine, and phentolamine blocked EFS (2 min, 80 V, 0.1-ms duration)-induced constriction. The constrictions and the endogenous norepinephrine levels were lower (P < 0.01) in uterine arteries from pregnant than from nonpregnant patients. When arterial rings were precontracted, the response to EFS was biphasic, consisting of an initial constriction followed by a postconstriction relaxation. The EFS-induced relaxation was endothelium independent and was greater (P < 0.01) in uterine arteries from pregnant than from nonpregnant patients. The relaxation was enhanced by guanethidine and superoxide dismutase, inhibited by nitric oxide synthase inhibitors, blocked by tetrodotoxin, and unaffected by atropine, propranolol, or indomethacin. The results demonstrate that human uterine arteries respond to EFS with contraction and relaxation and that these responses may be mediated, respectively, by norepinephrine and, in part, by nitric oxide released from periarterial nerves. The decrease in neuronally mediated uterine arterial constriction and the increase in dilation could be physiological mechanisms for ensuring appropriate uteroplacental perfusion.
Na+/Ca2+ exchange and cell contraction in isolated neonatal and adult rabbit cardiac myocytes
Authors: Wetzel G. T. , Chen F. , Klitzner T. S.
Published: December 2017

Recent studies have demonstrated a relative deficiency in voltage-gated Ca2+ currents (ICa) in immature myocardium. We hypothesized that contraction in developing heart results in part from Ca2+ influx via “reverse” Na+/Ca2+ exchange current (INa/Ca). Accordingly, INa/Ca and cell contraction amplitude were measured in single neonatal and adult rabbit ventricular myocytes. INa/Ca was dependent on Ca2+ concentration, Na+ concentration, and membrane potential and was blocked by 5 mM Ni2+ but not by the Ca(2+)-channel blocker nifedipine. In neonatal cells, contraction amplitude reached a plateau for depolarizations positive to 0 mV. In adult myocytes, contraction amplitude was maximal at 0 mV and decreased at positive membrane potentials. Inhibition of ICa with nifedipine did not affect maximal contraction amplitude in neonatal myocytes but almost completely suppressed contraction of adult cells. These data suggest that Ca2+ influx via ICa is not required for contraction of neonatal rabbit cardiac myocytes. Moreover, Ca2+ influx via reversal of the Na+/Ca2+ exchange mechanism may provide a significant portion of the Ca2+ regulating cell contraction, especially during depolarization to positive membrane potentials.
Altered beta-adrenergic and muscarinic response of CFTR Cl- current in dialyzed cardiac myocytes
Authors: Zakharov S. I. , Harvey R. D.
Published: December 2017

Autonomic regulation of the cardiac cystic fibrosis transmembrane conductance regulator (CFTR) Cl- current was studied in isolated guinea pig ventricular myocytes using various configurations of the whole cell patch-clamp technique. When currents were recorded using the conventional patch-clamp technique, it was possible to continue to activate the Cl- current on repeated exposure to isoproterenol (Iso) for up to 60 min after initiating dialysis. However, there was significant rundown of the magnitude of the Cl- current response to the maximally stimulating concentrations of Iso. In addition, the concentration of Iso that produced half-maximal activation of the Cl- current (K1/2) increased with time. Conversely, the K1/2 for acetylcholine inhibition of the Iso-activated current decreased with time. When currents were recorded using the perforated patch-clamp technique, the sensitivity to both beta-adrenergic- and muscarinic-receptor stimulation was stable. Immediately after initiation of dialysis with the conventional patch-clamp technique, the sensitivity to Iso was nearly identical to that determined using the perforated patch-clamp technique. However, the initial sensitivity to muscarinic-receptor activation was significantly greater. These results indicate that cell dialysis associated with conventional patch-clamp techniques not only results in a time-dependent rundown of current amplitude, but it also significantly alters the concentration dependence of beta-adrenergic and muscarinic-receptor regulation of ion channel function.
Indirect stimulation of Ca(2+)-activated Cl- current by Na+/Ca2+ exchange in rabbit portal vein smooth muscle
Authors: Leblanc N. , Leung P. M.
Published: December 2017

Macroscopic currents were recorded in freshly dissociated smooth muscle cells from the rabbit portal vein using the tight seal whole cell recording mode (22 degrees C). In some experiments, the indo 1 fluorescence technique was used to simultaneously monitor the changes in the concentration of free intracellular Ca2+ ([Ca2+]i; indo 1 ratio, 400/500 nm). In cells exposed to tetraethylammonium chloride (TEA) to inhibit K+ channels and 1-10 microM nifedipine or nicardipine to inhibit L-type Ca2+ channels, cell dialysis with 30 mM Na+ increased [Ca2+]i and induced membrane current consistent with the activation of Ca(2+)-activated Cl- channels [ICl(Ca)]. From holding potential (HP) of -60 mV, high intracellular Na+ concentration ([Na+]i)-mediated current was instantaneous in response to 0.5- to 10-s voltage clamp pulses from -80 to +20 mV; steps ranging from +20 to +80 mV evoked slow time-dependent outward current (I(t); superimposed on the instantaneous current) and voltage-dependent Ca2+ transient; on return to HP, slow inward tail current appeared that reflected deactivation of I(t). Both current components 1) exhibited outward rectifying properties, 2) reversed near the predicted equilibrium potential for Cl-, 3) were stimulated by elevation of extracellular Ca2+ concentration, 4) were abolished when the cells were dialyzed with 5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and 5) were inhibited by extracellular application of niflumic acid (50 microM). Complete replacement of extracellular Na+ concentration with tetramethylammonium increased both the instantaneous and time-dependent components of ICl(Ca), resting [Ca2+]i at -60 mV and Ca2+ transient at +40 mV. Cell dialysis with Na(+)-free pipette solution prevented these effects. Our results are consistent with an indirect mechanism of stimulation of ICl(Ca), which involves intracellular Ca2+ accumulation via reverse-mode electrogenic Na+/Ca2+ exchange activity.
EDRF and norepinephrine-induced vasodilation in the canine coronary circulation
Authors: Van Bibber R. , Traub O. , Kroll K. , Feigl E. O.
Published: December 2017

Experiments were performed to characterize the role of endothelium-derived relaxing factor (EDRF) in coronary vasodilation caused by norepinephrine. The circumflex or left anterior descending coronary artery was cannulated and pump perfused with constant pressure or constant flow in closed-chest anesthetized dogs. Prostaglandin synthesis was blocked with ibuprofen. During constant-pressure perfusion, EDRF inhibition with intracoronary N omega-nitro-L-arginine (L-NNA) did not affect the vasodilation due to nitroglycerin (an endothelium-independent process). However, L-NNA did significantly inhibit (P < 0.001) the vasodilation due to acetylcholine (an endothelium-dependent process). In response to bolus injections of norepinephrine, EDRF inhibition with L-NNA significantly reduced coronary vasodilation (P < 0.001). This inhibition was partially reversed with L-arginine infusion. To determine whether an increase in shear stress due to an increase in flow was the stimulus for EDRF release, experiments were performed during constant-flow conditions. Vasodilation caused by nitroglycerin was not inhibited by L-NNA, but EDRF inhibition did blunt acetylcholine-induced vasodilation significantly (P < 0.001) during constant-flow perfusion. During EDRF inhibition with L-NNA, vasodilation due to norepinephrine was not significantly altered when coronary flow was held constant (P = 0.19). In conclusion, EDRF plays a role in norepinephrine-induced coronary vasodilation that is largely flow dependent.
Potentiation of angiotensin II-stimulated vascular contraction by lithium
Authors: Ullian M. E. , Walsh L. G. , Wong K. C. , Allan C. J.
Published: December 2017

Previous studies have suggested that lithium prolongs or enhances vascular contractions stimulated by alpha-adrenergic agents. The present study was performed to determine whether a similar phenomenon occurs with angiotensin II (ANG II)-stimulated contractions and whether this phenomenon results from interactions with the phosphoinositide signaling system. Contractions of rat aortic rings with 100 nM ANG II were 38% greater in the presence of 20 mM LiCl than in its absence (0.47 +/- 0.07 vs. 0.34 +/- 0.05 g tension/mg dry tissue wt, P < 0.01). The effects of lithium on inositol phosphate responses, diacylglycerol responses, and intracellular calcium concentration on single or repeated stimulations with ANG II were then examined in vascular smooth muscle cells cultured from rat aorta. Cells exposed twice to 100 nM ANG II contained 50% lower inositol trisphosphate levels (InsP3) and 10% lower diacylglycerol levels than cells exposed to ANG II only once. LiCl or lithium acetate abolished these desensitizations in a concentration-dependent manner. Similarly, InsP3 and diacylglycerol responses to a single exposure of ANG II were heightened by lithium (by 75 and 25%, respectively), and the duration of the responses was prolonged by lithium (5- and 2-fold, respectively). In contrast, ANG II-stimulated calcium transients were not enhanced or prolonged by lithium, nor was desensitization of ANG II-stimulated cytosolic calcium mobilization upon serial exposures abolished by lithium. When ring contraction studies were repeated in the presence of the protein kinase C inhibitor staurosporine (150 nM), lithium no longer potentiated ANG II contractions [0.38 +/- 0.03 (control) vs. 0.35 +/- 0.06 g tension/mg dry tissue wt (lithium)].(ABSTRACT TRUNCATED AT 250 WORDS)
Selective reduction of PVR by inhalation of a cGMP analogue in a porcine model of pulmonary hypertension
Authors: Lawson C. A. , Smerling A. J. , Naka Y. , Burkhoff D. , Dickstein M. L. , Stern D. M. , Pinsky D. J.
Published: December 2017

Selective reduction of pulmonary vascular resistance (PVR) remains a therapeutic goal for the treatment of pulmonary hypertension, but current therapeutic options remain limited. Although the gas nitric oxide (NO) selectively dilates the pulmonary vascular bed, it requires special equipment for administration, has a short biologic half-life, and is potentially toxic. We hypothesized that stimulation of the NO pathway at the level of its second messenger, guanosine 3',5'-cyclic monophosphate (cGMP), by targeted pulmonary delivery of a membrane-permeable nonhydrolyzable cGMP analogue would cause selective pulmonary vasodilation. Pulmonary hypertension was induced in 21 pigs by the intravenous infusion of a thromboxane A2 analogue (9,11-dideoxy-9 alpha,11 alpha-epoxymethanoprostaglandin F2 alpha). Inhaled 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) lowered PVR in a time- and dose-dependent manner, with maximal effect achieved after 20 min. Compared with physiological saline control, 8-BrcGMP inhalation (3.0 micrograms/kg) lowered PVR by 25 +/- 3% (P < 0.01), whereas there was no significant decline in systemic vascular resistance (4 +/- 6%); mean pulmonary arterial pressure declined 13 +/- 3% (P < 0.01), whereas there was little change in mean arterial pressure; cardiac output increased 10 +/- 4% (P < 0.05). PVR did not decrease after inhalation of noncyclic 8-bromoguanosine 5'-monophosphate, indicating that stimulation of the NO-cGMP pathway beyond the level of NO results in pulmonary vasodilation independent of stimulation of purinergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Large artery remodeling after myocardial infarction
Authors: Gaballa M. A. , Raya T. E. , Goldman S.
Published: December 2017

Rats with myocardial infarction (MI) after coronary artery ligation (n = 75) and sham operated rats (n = 40) were treated with captopril (2 g/l drinking water), hydralazine (80 mg/l drinking water), or untreated water for 3 wk. Arterial hemodynamics, carotid artery mechanical properties, and water permeability were measured. Arterial wall stress and interstitial fluid velocity were calculated. In infarcted rats, the characteristic impedance at matched pressure was increased by 135% (P < 0.02); captopril and hydralazine decreased characteristic impedance (P < 0.015). MI altered the material constants; captopril but not hydralazine normalized these constants. Water permeability was increased by 221% (P < 0.001) in infarcted rats; captopril but not hydralazine reversed water permeability (P < 0.05). MI resulted in a 59% increase (P < 0.05) in the arterial collagen area and a 22% decrease (P < 0.05) in the media thickness. Captopril but not hydralazine decreased (P < 0.03) collagen area. In conclusion, 1) arterial remodeling defined by alterations in the passive mechanical properties, water permeability, and structure occurs in rats after MI; and 2) captopril but not hydralazine reverses the arterial remodeling.
Effects of chronic NO synthase inhibition in rats on renin-angiotensin system and sympathetic nervous system
Authors: Zanchi A. , Schaad N. C. , Osterheld M. C. , Grouzmann E. , Nussberger J. , Brunner H. R. , Waeber B.
Published: December 2017

This study was designed to assess the role of renin and of the sympathoadrenal system in the maintenance of the hypertension induced by chronic nitric oxide synthase (NOS) inhibition in rats kept on a normal (RS) or a low-sodium (LS) diet. With the administration of NG-nitro-L-arginine methyl ester (L-NAME) in drinking water (0.4 milligrams) for 6 wk, mean intra-arterial blood pressure rose to a similar extent to 201 mmHg in the RS and 184 mmHg in the LS animals. Simultaneously, plasma norepinephrine was increased to 838 and 527 pg/ml and epinephrine to 2,041 and 1,341 pg/ml in RS and LS, respectively. Plasma neuropeptide Y levels did not change. Plasma renin activity rose to 21 ng.ml-1.h-1 in RS but remained at 44 ng.ml-1.h-1 in the LS. Both losartan (10 mg/kg) and phentolamine (0.1 mg/kg) intravenous bolus injections reduced blood pressure considerably in the L-NAME hypertensive animals. Whole brain NOS activity was reduced by 84%. Hypertension induced by chronic NOS inhibition in LS as well as in RS fed rats seems to be sustained by an interaction of several mechanisms, including the activation of the sympathetic nervous system and the renin-angiotensin system.
Possible regulation of renin release by ANP in dogs with heart failure
Authors: Kanamori T. , Wada A. , Tsutamoto T. , Kinoshita M.
Published: December 2017

We investigated whether atrial natriuretic peptide (ANP) contributed to the regulation of renin release during the development of experimental heart failure in dogs. Significant increases of plasma ANP and plasma guanosine 3',5'-cyclic monophosphate (cGMP) levels were observed in dogs with mild heart failure induced by 6 days of rapid ventricular pacing. However, plasma renin activity (PRA) was not elevated, despite the significant decreases in renal plasma flow and mean arterial pressure. An inverse correlation between PRA and the ratio of plasma cGMP to ANP (rs = -0.59, P < 0.05) was found in dogs subjected to 9 days of rapid pacing. In dogs with advanced heart failure induced by 15-24 days of rapid pacing, the plasma cGMP level did not increase further, despite the progressive increase in plasma ANP with the resultant significant increase in PRA (P < 0.05). These findings suggest that attenuation of the inhibitory effect of ANP on renin release during the development of severe heart failure may be an important factor in the activation of the renin-angiotensin system.
Role of nitric oxide in regulation of long-term pressure-natriuresis relationship in Dahl rats
Authors: Hu L. , Manning R. D.
Published: December 2017

The aim of this study was to determine the role of nitric oxide (NO) in the development of salt-induced hypertension in the Brookhaven strain of Dahl rats. Six- to seven-week-old conscious salt-sensitive (S) and salt-resistant (R) rats with indwelling arterial and venous catheters received low-, normal-, and high-sodium intakes sequentially over a 16-day period, and L-arginine was infused intravenously at 2 or 4 mg.kg-1.min-1 over this time. The S rats had an impaired NO production as evidenced by a decreased urinary nitrate plus nitrite excretion. The administration of the low or high dose of L-arginine increased the whole body NO production of the S rats to that of the control R rats, and the high dose of L-arginine prevented the shift of long-term pressure-natriuresis relationship, the elevation of arterial pressure, and the increase in salt sensitivity of arterial pressure in the S rats. The sodium and water balances were not different between the age-matched R and S rats. In conclusion, a continuous infusion of L-arginine prevented both the changes in the pressure-natriuresis relationship and the development of salt-induced hypertension in Dahl S rats.
Contractile and cytoskeletal content, structure, and mRNA levels with tachycardia-induced cardiomyopathy
Authors: Eble D. M. , Spinale F. G.
Published: December 2017

Chronic supraventricular tachycardia (SVT)-induced cardiomyopathy is associated with left ventricular (LV) dilatation, increased wall stress, neurohormonal activation, and no change in LV mass. To determine mechanisms for changes in LV geometry and function with SVT cardiomyopathy, LV and myocyte function, contractile protein content and mRNA levels, and cytoskeletal protein structure and mRNA levels were examined in 12 pigs with SVT cardiomyopathy (paced at 240 beats/min for 3 wk) and in 12 controls. With SVT cardiomyopathy, LV fractional shortening fell by 61%, and end-diastolic dimension increased by 42%, with no change in LV mass-to-body weight ratio (3.36 +/- 0.15 vs. 3.14 +/- 0.13 g/kg). Myocyte contractile function was reduced by 33%, myocyte length was increased by 28%, and cross-sectional area was decreased by 19% with SVT cardiomyopathy. Total protein, myosin heavy chain (MHC), and actin appeared unchanged with SVT cardiomyopathy at the LV or myocyte level. Moreover, there was no change in mRNA levels for MHC (0.57 +/- 0.05 vs. 0.59 +/- 0.09 mRNAOD/rRNAOD) or cardiac alpha-actin (0.58 +/- 0.08 vs. 0.58 +/- 0.04 mRNAOD/rRNAOD) with SVT cardiomyopathy. In contrast, mRNA levels for specific cytoskeletal proteins were significantly increased with SVT cardiomyopathy, and immunofluorescent localization of contractile and cytoskeletal proteins in isolated myocytes revealed alterations in cytoskeletal architecture. Thus changes in LV and myocyte geometry with SVT cardiomyopathy were associated with no change in contractile protein content or mRNA at the chamber or myocyte level. Furthermore, increased cytoskeletal protein abundance and mRNA and reorientation of cardiocyte cytoarchitecture may have contributed to the LV and myocyte remodeling with SVT cardiomyopathy.
Growth effects of electrically stimulated contraction on adult feline cardiocytes in primary culture
Authors: Kato S. , Ivester C. T. , Cooper G. , Zile M. R. , McDermott P. J.
Published: December 2017

The purpose of this study was to determine effects of long-term electrical stimulation of cardiocyte contraction on protein synthesis rates and total protein content. Adult feline cardiocytes were plated on laminin-coated culture trays and maintained in a serum-free medium consisting of M199 supplemented with ascorbate, bovine serum albumin, creatine, carnitine, taurine, and 10(-7) M recombinant insulin. Cardiocytes were electrically stimulated to contract with use of continuous electrical pulses of alternating polarity at a frequency of 1 Hz and pulse duration of 5 ms. Nonstimulated cardiocytes are normally quiescent and were used as the control group. In control quiescent cardiocytes, protein synthesis rate decreased by 14% between days 1 and 4 in culture and then remained stable through day 7. In electrically stimulated cardiocytes, protein synthesis rates increased by 19% between days 1 and 7. Protein synthesis rates were 18% higher on day 4 and 43% higher on day 7 in electrically stimulated than in quiescent cardiocytes. Protein content per cell was determined by measuring total fluorescence per cell by use of confocal microscopy of fluorescein isothiocyanate-stained cells. Electrical stimulation significantly increased cellular protein content by 52% after 7 days compared with controls. Quiescent and electrically stimulated cardiocytes remained rod shaped, retained their myofibrillar architecture, and were responsive to electrical stimulation over the 7-day period. These data demonstrated that electrically stimulated contraction of adult cardiocytes resulted in cell growth, as assessed by an increase in protein content per cell over 7 days in culture. This increase was due, at least in part, to an acceleration of steady-state protein synthesis rates.
Mechanism of mechanical alternans in ischemia-reperfusion: role of deficient relaxation of the strong twitch
Authors: Nwasokwa O. N.
Published: December 2017

We tested the hypothesis that impaired and incomplete relaxation of the strong twitch of mechanical alternans causes the peak force deficit (PFD) of the weak twitch and that, by decreasing the relaxation deficit (RD) of the strong twitch, dobutamine would diminish the PFD. We studied isometric twitches of the in situ blood-perfused canine papillary muscle (n = 8). To produce mechanical alternans, we paced the heart at 110-155 beats/min and decreased mean coronary perfusion pressure (MCPP) stepwise to produce ischemia and then increased it to produce reperfusion. We measured the RD and PFD and fit each curve of isometric force [F(t)] with the relation F(t) = F0 + C(t/A)Be1-(t/A)B, where F0 is force at twitch onset, to obtain the parameters A, B, and C. B is a dimensionless index of myocardial relaxation; it decreases with impaired (delayed) relaxation. At each MCPP, we averaged B for the strong and weak twitches. The PFD showed a positive correlation with the RD. At each MCPP, mean B was lower for the strong twitch than for the weak twitch, indicating impaired relaxation of the strong twitch. Dobutamine increased B from 1.83 +/- 0.14 to 2.12 +/- 0.16 (P = 0.00002) in the strong twitch and decreased B from 4.15 +/- 2.42 to 2.19 +/- 0.18 (P = 0.05) in the weak twitch. Dobutamine thus equalized the relaxation of the strong and weak twitches. Consequently it decreased the RD from 2.57 +/- 2.14 to 0.16 +/- 0.24 g (P = 0.01) and the PFD from 5.50 +/- 3.67 to 1.04 +/- 1.15 g (P = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Cytoskeleton modulates gating of voltage-dependent sodium channel in heart
Authors: Undrovinas A. I. , Shander G. S. , Makielski J. C.
Published: December 2017

To investigate the role of the cytoskeleton in cardiac Na+ channel gating, the action of cytochalasin D (Cyto-D), an agent that interferes with actin polymerization, was studied by whole cell voltage clamp and cell-attached and inside-out patches from rat and rabbit ventricular cardiac myocytes. Cyto-D (20-40 microM) reduced whole cell peak Na+ current by 20% within 12 min and slowed current decay without affecting steady-state voltage-dependent availability or recovery from inactivation. Brief treatments (< 10-15 min) of cell-attached patches by Cyto-D (20 microM) in the bath induced short bursts of Na+ channel openings and prolonged decays of ensemble-averaged currents. Bursting of the Na+ channel was more pronounced when the cell suspension was pretreated with Cyto-D (20 microM) for 1 h before seal formation. Application of Cyto-D on the cytoplasmic side of inside-out patches resulted in more dramatic gating changes. Peak open probability was reduced by > 50% within 20 min, and long bursts of openings occurred. Washout of Cyto-D did not restore ensemble-averaged current amplitude, but burst duration decreased toward control values. Cyto-D also induced an additional slower component to open and closed times. These results suggest that Cyto-D, through effects on cytoskeleton, induced cardiac Na+ channels to enter a mode characterized by a lower peak open probability but a greater persistent activity as if the inactivation rate was slowed. The cytoskeleton, in addition to localizing integral membrane proteins, apparently also plays a role in regulating specific detailed functions of integral membrane proteins such as the gating of Na+ channels.
Effect of acidosis on hydrogen peroxide injury to the isolated perfused rat heart
Authors: Evans T. , Jin H. , Elkins N. , Shapiro J. I.
Published: December 2017

We observed that both low and high doses of H2O2 (100 microM and 1 mM, respectively) caused significant and irreversible injury to cardiac contractile function in the isolated perfused heart model. Using 31P-nuclear magnetic resonance spectroscopy, we observed marked metabolic changes following exposure to H2O2, especially at the 1 mM dose. Most remarkable were the increases in the intensity of the phosphomonoester resonance that occurred immediately after exposure to H2O2. The major phosphomonoester species accumulating in hearts exposed to 1 mM H2O2 appears to be AMP. Exposure of hearts to H2O2 in the setting of metabolic acidosis did not significantly alter the functional response of isolated hearts to H2O2. However, the increases in phosphomonoester peak intensity following both doses of H2O2 and the decreases in tissue ATP and total phosphates following 1 mM H2O2 were attenuated by metabolic acidosis.
Enhanced postischemic myocardial recovery following exercise induction of HSP 72
Authors: Locke M. , Tanguay R. M. , Klabunde R. E. , Ianuzzo C. D.
Published: December 2017

The inducible isoform of the 70-kDa heat shock protein (HSP) family, HSP 72, has been shown to protect cells from protein-damaging stressors and has been associated with myocardial protection. Because exercise is capable of increasing HSP 72 content, we determined whether exercise induction of HSP 72 also provided myocardial protection. Twenty-eight rats (n = 7 per group) were divided into control, heat-shocked (15 min at 42 degrees C), and two exercised groups. Exercise consisted of either one or three bouts (on 3 consecutive days) of treadmill running for 60 min at 30 m/min. Twenty-four hours after heat shock or exercise, hearts were placed on a Langendorff apparatus and subjected to 30 min of global ischemia followed by 30 min of reperfusion. Left ventricular developed pressure (LVDP), maximal rate of contraction and relaxation (+/- dP/dt, respectively), coronary flow, catalase activity, and HSP 72 content were determined. During reperfusion, hearts from heat-shocked animals and animals subjected to three bouts of exercise recovered a greater percentage of preischemic LVDP and +/- dP/dt compared with controls or animals that exercised only once. Compared with hearts from controls, HSP 72 content was significantly elevated in the hearts of heat-shocked animals and in animals subjected to three bouts of exercise, but not in animals that exercised only once. These results suggest that exercise induction of HSP 72 can confer an enhanced postischemic recovery and may explain, at least in part, the myocardial protection associated with exercise.
Regulation of membrane potential and diameter by voltage-dependent K+ channels in rabbit myogenic cerebral arteries
Authors: Knot H. J. , Nelson M. T.
Published: December 2017

The hypothesis that voltage-dependent K+ channels are involved in the regulation of arterial smooth muscle membrane potential and blood vessel diameter was tested by examining the effects of inhibitors [4-aminopyridine (4-AP) and 3,4-diaminopyridine (3,4-DAP)] of voltage-dependent K+ channels on the membrane potential and diameter of pressurized small (100- to 300-microns diam) cerebral arteries from rabbit. In response to graded elevations in transmural pressure (20-100 mmHg), the membrane potential of smooth muscle cells in these arteries depolarized and the arteries constricted. 4-AP (1 mM) and 3,4-DAP (1 mM) depolarized cerebral arteries by 19 and 21 mV, respectively, when they were subjected to a transmural pressure of 80 mmHg. 3-Aminopyridine (3-AP, 1 mM), which is a relatively poor inhibitor of voltage-dependent K+ channels, depolarized smooth muscle cells in the arteries by 1 mV. 4-AP and 3,4-DAP constricted pressurized (to 80 mmHg) cerebral arteries. 3-AP had little effect on arterial diameter. 4-AP increased the arterial constriction to transmural pressure over a wide range of pressures (40-90 mmHg). The effects of 4-AP and 3,4-DAP on membrane potential and diameter were not prevented by inhibitors of calcium channels, calcium-activated K+ channels, ATP-sensitive K+ channels, inward rectifier K+ channels, blockers of adrenergic, serotonergic, muscarinic, and histaminergic receptors, or removal of the endothelium. These results suggest that voltage-dependent K+ channels are involved in the regulation of membrane potential and response of small cerebral arteries to changes in intravascular pressure.
Effect of BDM, verapamil, and cardiac work on mitochondrial membrane potential in perfused rat hearts
Authors: Doumen C. , Wan B. , Ondrejickova O.
Published: December 2017

The biochemical link providing effective coordination between the mitochondrial ATP synthetic machinery and the contractile apparatus following transitions in cardiac work remains enigmatic. Studies were designed to determine whether activation of the actomyosin adenosinetriphosphatase (ATPase) is a necessary part of the signaling mechanism to the mitochondrial ATP synthase or whether a rise in cytosolic free Ca2+ is sufficient to activate the synthase. With the use of Langendorff-perfused rat hearts, cardiac work was varied via changes in perfusion pressure and by the inclusion of a beta-adrenergic agent. Furthermore, 2,3-butanedione monoxime and verapamil were used to vary independently either the activity of the actomyosin ATPase or the level of cytosolic free Ca2+. Determinations of the in vivo mitochondrial membrane potential [delta psi m; see Wan et al. Am. J. Physiol. 265 (Heart Circ. Physiol. 34): H445-H452, 1993] and its vectorial displacement during work transitions provide valuable information concerning direct activation of the ATP synthase and proton movement through the membrane domain of the synthase. Increased cardiac work in the presence of the beta-adrenergic agent resulted in a decrease in delta psi m. Addition of 2,3-butanedione monoxime decreased cardiac work but did not change delta psi m. The inclusion of verapamil resulted in similar decreases in cardiac work. However, delta psi m reversed back to a value observed under control, low-work conditions. These results in conjunction with data regarding levels of high-energy phosphates, free Mg2+, and adenosine 3',5'-cyclic monophosphate suggest a Ca(2+)-mediated increase in the activity of the ATP synthase.
Oxidative-stress response in vascular endothelial cells exposed to acellular hemoglobin solutions
Authors: Motterlini R. , Foresti R. , Vandegriff K. , Intaglietta M. , Winslow R. M.
Published: December 2017

We investigated the effect of different hemoglobins on the activation of endothelial heme oxygenase (HO), an inducible "stress" protein, which is responsible for heme catabolism, and we determined whether the propensity of hemoglobins to autoxidize correlates with endothelial heme uptake and cell injury. Porcine aortic endothelial cells were incubated for 6 h in the presence of 60 microM unmodified hemoglobin A0 (HbA0), hemoglobin cross-linked between the alpha-chains with bis-(3,5-dibromosalicyl)fumarate (alpha alpha Hb), or cyanomet-alpha alpha-hemoglobin (CNmet alpha alpha Hb). Endothelial HO activity augmented 4.1-fold in the presence of alpha alpha Hb, 2.7-fold with HbA0, and 1.8-fold with CNmet alpha alpha Hb over the control value. Deferoxamine, but not catalase or dimethylthiourea, partially attenuated the HO induction produced by alpha alpha Hb. The rates of methemoglobin formation exhibited a linear relationship over the time of incubation (r = 0.94), and the apparent rate constant was 1.8-fold higher for alpha alpha Hb (0.023 h-1) than for HbA0 (0.013 h-1). Endothelial heme content and lactate dehydrogenase (LDH) release, an index of cell injury, were also higher in alpha alpha Hb compared with HbA0 and CNmet alpha alpha Hb groups (P < 0.05). Deferoxamine but not catalase markedly reduced the release of LDH induced by alpha alpha Hb, whereas dimethylthiourea provided only a partial cytoprotection. These studies suggest that 1) the higher rate of oxidation of alpha alpha Hb contributes to the augmented endothelial HO activity, and 2) both heme release and iron-mediated oxygen radical formation are major contributors to endothelial oxidative stress and cytotoxicity generated by the cross-linked hemoglobin.
Proliferation and migration of endothelial cells is promoted by endothelins via activation of ETB receptors
Authors: Morbidelli L. , Orlando C. , Maggi C. A. , Ledda F. , Ziche M.
Published: December 2017

The growth and migration of endothelial cells are the prerequisites for vascular remodeling. The effects of endothelin (ET)-1 and -3 (ET-1, ET-3) on the proliferation and migration of endothelial cells isolated from bovine adrenal capillaries (BACE) and human umbilical veins (HUVEC) have been investigated. Cell proliferation (measured as DNA synthesis and as total cell number) and migration were significantly increased by ET-1 and ET-3. Dose-dependent proliferation was produced by ET-1 and ET-3 in both cell lines, with maximal effects at 0.1 nM concentration. ET-1 and ET-3 also stimulated BACE and HUVEC mobilization in a dose-dependent manner. The maximal responses were obtained at 10 nM concentration in both BACE and HUVEC. The full agonist for the ETB receptor, ET-(16--21), was able to reproduce the effects of ET on proliferation and migration of both cell lines. Modification of ET-(16--21) at Leu17 and Ile19 and amidation of the COOH-terminal were accompanied by loss of activity. The ETB-receptor antagonist IRL-1038 blocked the migration induced by ET-3 and ET-(16--21), whereas the ETA-receptor antagonist BQ-123 was not effective. We conclude that ETs, by favoring endothelial cell growth and mobilization, can contribute to neovascularization through an autocrine mechanism that requires ETB-receptor activation.
Effect of norepinephrine and acetylcholine on outer medullary descending vasa recta
Authors: Yang S. , Silldorff E. P. , Pallone T. L.
Published: December 2017

To examine their responsiveness to norepinephrine (NE) and acetylcholine (ACh), outer medullary descending vasa recta (OMDVR) have been dissected from vascular bundles of the rat and perfused in vitro. Abluminal application of NE produced graded vasoconstriction in a concentration range of 10(-9)-10(-6) M. When applied with NE, ACh at concentrations of 10(-8)-10(-5) M dilated NE-preconstricted OMDVR. In contrast, ACh applied in the absence of NE caused vasoconstriction. ACh-induced vasodilation was blocked by addition of the nitric oxide synthase inhibitor N omega-nitro-L-arginine (L-NNA, 2 x 10(-4) M). L-NNA in the absence of ACh enhanced NE-induced vasoconstriction. Supraphysiological (10(-3) M) L-arginine (L-Arg) reversed the effects of L-NNA, and abluminal application of L-NNA alone resulted in OMDVR vasoconstriction. At concentrations of 10(-6)-10(-3) M, abluminal application of L-Arg produced graded vasodilation of NE-constricted OMDVR. These results suggest that adrenergic and cholinergic innervation could influence OMDVR vasomotor tone to modulate total and regional blood flow to the renal medulla. The data also favor a role for the activity of constitutively expressed nitric oxide synthase to modulate OMDVR vasoactivity.