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Taurine neither induces nor affects the Ca²⁺-dependent slow action potentials (AP), nor does it elevate cyclic-AMP levels; however, it increases the action potential duration. Although taurine does not stimulate the slow AP under normal conditions, under hypoxic conditions it does exert a stimulant effect and protects against the depression of the slow AP. These effects may be mediated either indirectly by stimulation of phosphorylation, or by a direct effect on one or more types of ionic channels. Thus, taurine’s action on heart cells is still ambiguous with respect to its electrophysiological effects. This project will try to elucidate the electrophysiological effects of taurine on heart muscle cells by applying the whole-cell configuration of the patch-clamp technique and using specific pharmacological blockers for I_Ca,L, I_Ca,T, I_Na and I_K. Preliminary studies suggest that taurine’s effect is mediated through the T-type and not through the L-type Ca²⁺ channels. G. Haddad. (Supported by AUB Medical Practice Plan.)

Taurine is found in millimolar concentrations in most animal tissues. It has been reported that taurine produces a positive inotropic effect in heart muscles, protects against calcium overload and is beneficial for treatment of myocardial infarction. Using conventional intracellular microelectrode techniques, contraction recordings and recordings of ionic currents, it was found that in adult heart cells taurine stimulated the low threshold T-type Ca²⁺ current in all ventricular heart cells tested including human and inhibited the hithreshold L-type Ca²⁺ current. The former effect depended on the extracellular free Ca²⁺ level. Those effects may be mediated indirectly by stimulation of phosphorylation or by a direct effect on one or more types of ionic channels. The present study is focusing on taurine’s intracellular effects and regulations of calcium channels through mitogen activating protein (MAP) kinases using the whole-cell configuration of the patch-clamp technique. G. Haddad. (Supported by URB.)

Cardiac hypertrophy is a pathological state which may be due to compensatory mechanism(s) allowing the heart to meet the increased workload. Insulin-growth factors (IGFs) have been shown to strongly stimulate cell proliferation and growth. Receptors for IGF-1 in the heart have been detected. Their effects are suggested to be mediated via cAMP signal transduction pathways which regulate intracellular Ca²⁺ levels. This project is to study the regulation of intracellular Ca²⁺ levels by IGF-1 through the slow Ca²⁺ inward currents and to study IGF-1 receptor kinetics and modulation in the hypertrophied hearts of adult male Sprague-Dawley rats. Cardiac hypertrophy will be induced by creating an arterio-venous shunt (aorta-caval). IGF1 receptor kinetics will be studied by using the established heart perfusion method. Patch-clamp technique in the whole-cell configuration will be used in order to study the slow calcium channel and the importance of the cAMP signal transduction pathway in mediating IGF-1 effects during cardiac hypertrophy. G. Haddad and A. Bikhazi. (Supported by LNCSR; AUB Medical Practice Plan.)

Role of endothelial factors and angiotensin II in amphotericin B nephrotoxicity

The mechanism of the nephrotoxic effect of the antifungal agent amphotericin B was examined in an acute model of nephrotoxicity in the rat. The role of nitric oxide (NO), endothelin and angiotensin II were examined using L-arginine and N-nitro-L-arginine (NNA) as agonist and antagonist of NO synthesis and using receptor antagonists of endothelin and angiotensin II, PD145065 and L158809, respectively. Treatment with amphotericin B caused 40-50% reduction in glomerular filtration rate (GFR) and renal plasma flow (RPF). Both effects were prevented by prior treatment with either NNA or excess L-arginine. Neither PD145065 nor L158809 altered the responses to amphotericin B. The study suggests that amphotericin B inhibits basal production of the vasodilator NO leading to vasoconstriction and reduced GFR. Prior inhibition (NNA) or enhancement (L-arginine) of NO synthesis may protect against these effects. The renal toxicity of amphotericin B may partially be explained by a toxic effect on the endothelium. R. Sabra. (Supported in part by URB.)

Comparison between the antifungal and nephrotoxic effects of amphotericin B and liposomal amphotericin B

Liposomal amphotericin B is a new preparation of the drug that is claimed to be less nephrotoxic while maintaining equivalent antifungal activity compared to amphotericin B. However, there is no definitive evidence in the literature to support this claim. The present project compares the effects of each formulation on: 1) renal function and hemodynamics after acute intravenous injections; 2) fungal infestation in in-vivo models of fungal infections in rats; 3) fungal cell viability in-vitro by evaluating minimal inhibitory concentrations of each formulation against several fungal pathogens; and 4) intracellular calcium levels in cultured glomerular mesangial cells and on their contractility using spectrofluorometric techniques which reflects the in vivo effects of vasoconstriction. The purpose is to estimate in vivo and in vitro safety indexes for each formulation which would indicate whether the liposomal preparation is advantageous over the classical one. R. Sabra. (Supported in part by LNCSR.)

Influence of phenobarbital on renal and systemic hemodynamics and on renal function in portal hypertensive rats

Our recent studies indicate that renal sodium retention in animal models of cirrhosis occurs only when liver function (assessed by the aminopyrine breath test) decreases below a critical threshold. This could reflect the role of critical liver metabolic processes in controlling renal function through influencing the synthesis of neuro-humoral factors. The relationship between liver function and renal function is being studied and further characterized in an animal model of liver dysfunction and portal hypertension. Since phenobarbital is known to stimulate liver enzymes, its effect on the renal and systemic consequences of liver dysfunction are being examined. R. Sabra. (Supported by AUB Medical Practice Plan.)

Mechanisms of potentiation by cocaine of adrenergic responses: possible role for beta adrenoceptor sensitization

The mechanism by which cocaine potentiates the effects of catecholamines is believed to be inhibition of reuptake by the nerve terminals. However, a number of in vitro studies suggest actions at the post-synaptic terminal. The first part of this proposal looking at the interaction of adrenergic agonists, the alpha adrenoceptor antagonist phenoxybenzamine and cocaine, has been completed. The results support the suggestion that cocaine acts by enhancing cardiac responses to adrenergic agonists at the beta adrenoceptor level and not only by inhibiting uptake of neurotransmitters, indicating a possible sensitization of cardiac beta-adrenergic receptors by cocaine. This possibility will be explored further in in vivo studies in cats, and in in vitro studies using membrane fractions and whole cells to examine the influence of cocaine and other related compounds on the number and properties of the beta-adrenoceptors in the heart. R. Sabra. (Supported in part by LNCSR.)

The effect of amiodarone on the electrophysiological and cardiodynamic effects of ouabain

Pretreatment of the isolated heart in a heart-lung preparation with amiodarone resulted in depression in myocardial contractility. An infusion of ouabain, subsequently administered, restored myocardial contractility to the control level and then produced a maximal increase in contractility not different from that observed with infusions of ouabain in control preparations. Continuation of the infusion produced arrhythmias different in pattern than those observed with ouabain alone. Confirmation of these initial observations and exploration of mechanisms are in progress. J. A. Simaan. (Supported by LNCSR.)

Comparison of the effect of different parasympathomimetic agents on the electrophysiological and cardiodynamic effects of ouabain

Acetylcholine, methacholine and pilocarpine, representing drugs that activate muscarinic receptors, were administered to the isolated heart in a heart-lung preparation, followed by an infusion of ouabain until cardiac standstill. Initial observations revealed that whereas acetylcholine alone produced a biphasic effect of initial increase in heart rate and myocardial contractility followed in higher doses by depression, the remaining parasympathomimatic agents produced primary and continued depression in heart rate and a much lesser depression in contractility. All the agents used modified the electrophysiological behavior of ouabain subsequently administered. Confirmation of these initial results and exploration of mechanisms involved are underway. J. A. Simaan and C. Farhat. (Supported by LNCSR.)

The cardiodynamic and electrophysiological effects of the calcium channel blockers in the cat heart-lung preparation and their interaction with ouabain

A comparative study of the direct effects of the calcium channel blocking agents, verapamil, nifedipine and isradipine, in the absence of autonomic modulation, was explored in the isolated heart-lung preparation from cats. In addition, the interaction between these agents and ouabain, representing the class of cardiac glycosides, was also explored, the justification being that the combined use of these agents in patients with myocardial failure and other cardiovascular problems such as angina, arrhythmias and hypertension is not uncommon. The resultsshow that the three blockers have quantitatively and qualitatively different effects on myocardial function, particularly as concerns myocardial contractility and heart rate. Furthermore, these agents modified the pharmacologic effects of ouabain differently. The initial conclusions drawn from these observations are that these calcium channel blockers have different selectivity in blocking the calcium channels involved in the various phases of the action potential and act differently on different cardiac cells. J. A. Simaan and R. M. Younis. (Supported by LNCSR.)

The direct and indirect vasodilator effects of acetylcholine, histamine and adenosine

The vasodilator effects of acetylcholine, histamine and adenosine were explored in the isolated autoperfused vascular beds of the hind limb and mesentery of the cat, under control conditions and following blockade of nitric oxide synthesis with l-nitroarginine. The results show that the hind limb vascular bed is more sensitive to the effect of vasorelaxants than the mesenteric vascular bed and that blockade of nitric oxide synthesis attenuates but does not completely block the effect of these vascular relaxants, implying that part of the relaxation observed with these agents could be a direct effect or mediated by other mechanisms not related to nitric oxide, including possibly the release of an endothelium-derived hyperpolerizing factor. J. A. Simaan and B. Ziade. (Supported by LNCSR.)

Bkaily, G.*, Haddad, G., Gros-Louis, N.*, Jaalouk, D.*, Taoudi Benchekroun, R.*, Naik, P.*, Pothier, P.*, D’Orleans-Juste, P.*, Bui, M.*, Wang, S.*, and Sperelakis, N.*, Modulation of Ca²⁺ and Na⁺ transport by taurine in heart and vascular smooth muscle. Advances in Experimental Medical Biology, (Taurine 2), 28, 263-273, 1996.

Haddad, G., Amiri, F.* and Garcia, R.*, Modulation of renal glomerular angiotensin II receptors by ACE inhibition and AT₁ receptor antagonism. Regulatory Peptides, 68, 11-117, 1997.

Haddad, G., and Garcia, R.*, Characterization and hemodynamic implications of renal vascular angiotensin II receptors in SHR. Journal of Molecular and Cellular Cardiology, 28, 351-361, 1996.

———, Effect of angiotensin converting enzyme two-week inhibition on renal ANG II receptors, and reactivity of renal vessels of the SHR. Journal of Molecular and Cellular Cardiology, 29, 813-822, 1997.

Murakami, S.*, Bernardo, J.F.*, Branch, R.A.* and Sabra, R., Adenosine does not contribute to sodium retention and peripheral vasodilation induced by partial portal vein ligation in rats. Hepatology, 23, 346-352, 1996.

Murakami, S.*, Bernardo, J.F.*, Jacob, T.D.*, Branch, R.A.* and Sabra, R., Nitric oxide does not contribute to sodium retention and peripheral vasodilation induced by partial portal vein ligation in rats. Renal Physiology and Biochemistry, 18 (4), 198-208, 1995.

Murakami, S.*, Ohno, T.*, Bernardo, J.*, Pfeifer, C.A.*, Zhang, Y.*, Li, T.*, Dubey, R.K.*, Branch, R.A.* and Sabra, R., Reduced liver function is the trigger for renal sodium retention following portal vein ligation in the rat. Journal of Gastroenterology and Hepatology, 9, 850-856, 1996.

Wensing, G.*, Sabra, R. and Branch, R.A.*, Relationship between oxidative hepatic metabolism, urinary sodium excretion and sympathetic nerve activity in experimental cirrhosis in the rat. Zeitschrift fur Gastroenterologie, 33, 1-4, 1995.

Amiri F.*, Haddad G. and Garcia R.*, Modulation of renal glomerular angiotensin II receptors by ACE and AT₁ receptor antagonism. Dupont-Merck 1997 Losartan Award, American Society for Pharmacology and Experimental Therapeutics ’97, San Diego, USA, 1997.

Branch, R.A.* and Sabra, R., The Threshold Concept. International Falk Workshop: Surrogate Markers to Assess Efficacy of Treatment in Chronic Liver Diseases, Basel, Switzerland, Oct. 23-24, 1995.

Haddad, G.E., and Garcia, R.*, Treatment with ACE inhibitor modulates renal ANG II receptors, vascular reactivity and hypertrophy of the SHR. American Society for Pharmacology and Experimental Therapeutics ’97, San Diego, USA, 1997.

Major, S., Badr, S., Bahlawan, L., Khalil, R., Khogaoghlanian, T., Melhem, A., Richani, R., Younes, F., Khogali, M. and Sabra, R., Drug-related illness leading to hospitalization at the AUB Medical Center. Thirty-Second Middle East Medical Assembly, Beirut, Lebanon, May, 1997.

Sabra, R., Beshara, G., Sharaf, L. and Habbal, M.Z., Endothelial factors in amphotericin B (AmB) nephrotoxicity. FASEB Journal, 10 (3), A152, 1996.

Simaan J. and Younis R., The cardiodynamic and electrophysiologic effects of calcium channel blockers and their interaction with ouabain explored in the isolated heart. The Pharmacologist, 39 (1) 74, 1997.

Rammal, M., Studies on imipramine in the cat heart-lung preparation and its interaction with ouabain (1995). Advisor: J. A. Simaan.

Ziade, B., Nitric oxide involvement in the vasodilator responses to acetylcholine, histamine and adenosine in the intact hind limb and mesenteric vascular beds (1996). Advisor: J. A. Simaan.

Younis, R., Studies on the cardiodynamic and electrophysiologic effects of the calcium channel blockers, verapamil, nifedipine and isradipine in the cat heart-lung preparation and their interaction with ouabain (1996). Advisor: J. A. Simaan.