Peculiarities of Tetraethylammonium-Induced Blocking of Potassium Currents in Rat Retinal Ganglion Cells

Abstract

We studied the sensitivity of integral potassium currents in retinal ganglion cells (RGCs) of 21-day-old rats to the blocking action of tetraethylammonium (TEA) applied in concentrations of 0.25 and 1.0 mM. The currents were recorded using a patch-clamp technique in the whole-cell configuration using a voltage-clamp mode; retinal preparations were not subjected to enzymatic treatment. Potassium currents were induced by long-lasting (400 msec) depolarizing current pulses of increased intensities. Under the action of 0.25 mM TEA, the integral potassium current was blocked by 18 ± 5%, on average; the amplitude of the TEA-sensitive (blocked) component at the membrane potential of +40 mV was 0.75 ± ± 0.02 nA (n = 6). At 1.0 mM TEA, 32 ± 5% of the current was blocked, and the mean amplitude of the TEA-sensitive component was 1.12 ± 0.02 nA (n = 9). The effect of TEA was reversible; the relative intensity of the TEA-sensitive component in different cells varied within a wide range (from 3 to 38% at 0.25 mM TEA and from 12 to 54% at 1.0 mM). A comparison of the findings with the data reported earlier showed that the dependence of the intensity of TEA blocking within a 0.25 to 1.0 mM range is nonlinear; it appears that the 0.5 mM concentration is relatively close to the saturating one. Analysis of the obtained data shows that TEA applied in the tested concentrations blocks mostly the potassium current through Kv3.1/Kv3.2 channels; the effects of the blocker on other types of channels (Kv3.3/Kv3.4, Kv1.1, and BK) are, in any case, much less significant.