AHEART January 47/1

Hulme, J. T., and C. H. Orchard Effect of acidosis on transient outward potassium current in isolated rat ventricular myocytes. Am. J. Physiol. Heart Circ. Physiol. 278: H50–H59, 2000.—The effect of acidosis on the transient outward K1 current (Ito) of rat ventricular myocytes has been investigated using the perforated patch-clamp technique. When the holding potential was 280 mV, depolarizing pulses to potentials positive to 220 mV activated Ito in subepicardial cells but activated little Ito in subendocardial cells. Exposure to an acid solution (pH 6.5) had no significant effect on Ito activated from this holding potential in either subepicardial or subendocardial cells. When the holding potential was 240 mV, acidosis significantly increased Ito at potentials positive to 220 mV in subepicardial cells but had little effect on Ito in subendocardial cells. The increase in Ito in subepicardial cells was inhibited by 10 mM 4-aminopyridine. In subepicardial cells, acidosis caused a 18.57-mV shift in the steady-state inactivation curve. It is concluded that in subepicardial rat ventricular myocytes acidosis increases the amplitude of Ito as a consequence of a depolarizing shift in the voltage dependence of inactivation.