A slowly inactivating transient outward current in rat ventricular myocytes

Abstract

In rat ventricular myocytes we found two components of transient outward current, which could be discriminated time- and voltage-dependently. Besides the well known fastly inactivating transient outward current (i_to,f, τ=35±8ms, n=4) we investigated properties of a slowly inactivating transient outward current (i_to,s, τ=1.7±0.4s, n=4). Because of the slow inactivation process of i_to,s tail currents were observed at −25mV. The inactivation curve of i_to,f was characterized by a half-inactivation voltage of −58.4±1.4mV and a slope factor of 5.6±0.5mV (n=4). The inactivation curves of i_to,s and tail currents were nearly identical but significantly different from the i_to,f-curve. Half-inactivation voltages of i_to,s and tail currents were −87.5±6mV and −89.1±5mV (n=4), respectively. Slope factors were 10.3±2.9mV and 9.8 ±1.7mV (n=4). The activation gate of i_to,s was half-maximally opened at −11.5±2.6mV, and the slope factor was −10.6±1.7mV (n=3). i_to,s tail current reversed its direction at −62±3.2mV (n=5). This indicates, that i_to,s- current flow is carried mainly by potassium ions. I_to,s- current was not abolished by Tetrodotoxin (TTX) and Cd.