Modulation of the Extracellular Divalent Cation-inhibited Non-selective Conductance in Cardiac Cells by Metabolic Inhibition and by Oxidants

Abstract

The effect of metabolic inhibition and oxidative stress on the monovalent cation-permeable, extracellular divalent cation-inhibited non-selective conductance was investigated in ventricular myocytes at 22°C. Under whole-cell voltage-clamp, with L-type Ca2+channels blocked by nifedipine, and K+currents blocked by Cs+substitution for K+, removal of Ca2+oand Mg2+oinduced a non-selective current (INS-(Ca)o) in mouse, rabbit and rat cells. Removal of glucose increased INS-(Ca)oin the absence of Ca2+oand Mg2+o, but failed to induce this current in the presence of the divalent cations. Further inhibition of glycolysis by 2-deoxyglucose (DOG; 10 m m, in zero glucose) or of mitochondrial function by rotenone (10 μ m) or NaCN (5 m m) also failed to induce INS-(Ca)oin the presence of Ca2+oand Mg2+o. Even when given together, DOG and rotenone did not induce INS-(Ca)oin the presence of divalent cations. Preactivated INS-(Ca)owas increased by the oxidants thimerosal (50 μ m), diamide (500 μ m) and pCMPS (50μ m). However, none of these drugs nor NEM (1 m m) did elicit INS-(Ca)oin the presence of Ca2+oand Mg2+o. Exposure of rat myocytes to Ag+induced a current resembling INS-(Ca)o(reversing at −5 mV; blocked by 100 μ m Gd3+) even in the presence of divalent cations. The data indicate that metabolic inhibition only regulates activated INS-(Ca)obut does not induce the opening of closed channels, and that small oxidants like Ag+may induce INS-(Ca)oactivation by accessing at sites unavailable for larger molecules.