s-nitro-n-acetylpenicillamine and Arrhythmias--Cardiac

: In sinoatrial (SA) node cells, nitric oxide (NO) exerts a dual effect on the hyperpolarization-activated current, I(f), i.e. in basal conditions NO enhances I(f) whereas in the presence of beta-adrenergic stimulation it decreases it. Recent studies have shown that I(f) is present in ventricular myocytes from hypertrophied or failing hearts where it may promote abnormal automaticity. Since these pathological conditions are associated with increased sympathetic tone and upregulation of myocardial NO production, we set out to investigate whether I(f) is similarly modulated by NO in hypertrophied ventricular myocytes.. Left ventricular myocytes were isolated from 18-20-month-old spontaneously hypertensive rats (SHRs). Membrane current was measured under whole-cell or amphotericin-perforated patch-clamp conditions, at 35 degrees C.. Application of diethylamine-NO (DEA-NO, 1-100 microM) did not alter the amplitude or voltage dependence of activation of I(f) under basal conditions (half-activation voltage, V(h): control -82.9+/-2.6, DEA-NO -84.0+/-2.6 mV). Similarly, I(f) was not affected by the inhibition of endogenous NO production (L-NMMA, 500 microM) or guanylate cyclase (ODQ, 10 microM). Forskolin (10 microM) or isoprenaline (100 nM) elicited a positive shift in V(h) but subsequent application of DEA-NO did not further affect the properties of I(f).. Our results show that, unlike in SA node cells, in SHR ventricular myocytes basal and adrenergically stimulated I(f) is not modulated by exogenous NO or by constitutive NO or cGMP production.

Topics: Adenylyl Cyclases; Adrenergic beta-Agonists; Amphotericin B; Analysis of Variance; Animals; Arrhythmias, Cardiac; Cardiomegaly; Colforsin; Enzyme Inhibitors; Guanylate Cyclase; Hydrazines; Isoproterenol; Male; Membrane Potentials; Nitric Oxide Donors; Nitric Oxide Synthase; Nitrogen Oxides; omega-N-Methylarginine; Oxadiazoles; Patch-Clamp Techniques; Penicillamine; Pyridines; Rats; Rats, Inbred SHR; Sinoatrial Node

Nitric oxide (NO) may play an essential role for maintenance of cardiac function and perfusion, while endothelial dysfunction of atherosclerotic vessels may aggravate ischaemia/reperfusion injury. This paper investigates the role of nitric oxide in ischaemia/reperfusion injury in hearts with coronary atherosclerosis. Hearts of apolipoprotein E/LDL receptor double knockout (ApoE/LDLr KO) mice fed an atherogenic diet for 7-9 months were isolated and Langendorff-perfused with 40 minutes of global ischaemia and 60 minutes reperfusion, and funtion and infarction compared with hearts of C57BL/6 controls in the prescence or abscence of the NO-donor SNAP or the NOS inhibitor L-NAME. Hearts of animals with atherosclerosis were more susceptible to ischaemia/reperfusion injury than hearts of animals with healthy vessels, evident as more impaired left ventricular performance. SNAP protected function and reduced infarct size in atherosclerotic hearts, but the same concentration of SNAP was detrimental in normal hearts, perhaps due to NO-overproduction and peroxynitrite formation demonstrated immunohistochemically as increased formation of nitrosylated tyrosine. A low concentration of SNAP protected against ischaemia/reperfusion dysfunction in normal hearts. L-NAME decreased left ventricular performance in atherosclerotic hearts. These findings suggest that impaired endothelium dependent function contributes to reperfusion injury in coronary atherosclerosis.

Topics: Animals; Apolipoproteins E; Arrhythmias, Cardiac; Arteriosclerosis; Blotting, Western; Immunohistochemistry; In Vitro Techniques; Mice; Mice, Inbred C57BL; Mice, Knockout; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Penicillamine; Receptors, LDL; Reperfusion Injury; Troponin T