Voltage-dependent chloride conductance of the squid axon membrane and its blockade by some disulfonic stilbene derivatives.

Abstract

When giant axons of squid, Sepioteuthis, were bathed in a 100 mM Ca-salt solution containing tetrodotoxin (TTX) and internally perfused with a solution of 100 mM tetraethylammonium-salt (TEA-salt) or tetramethylammonium-salt (TMA-salt), the membrane potential became sensitive to anions, especially Cl-. Membrane currents recorded from those axons showed practically no time-dependent properties, but they had a strong voltage-dependent characteristic, i.e., outward rectification. Cl- had a strong effect upon the voltage-dependent membrane currents. The nonlinear property of the currents was almost completely suppressed by some disulfonic stilbene derivatives applied intracellularly, such as 4-acetoamido-4''-isothiocyanostilbene-2,2''-disulfonic acid (SITS) and as 4,4''-diisothiocyanostilbene-2,2''-disulfonic acid (DIDS), which are blockers of chloride transport. A voltage-dependent chloride-permeable channel exists in the squid axon membrane. The chloride permeability (PCl) is a function of voltage and its value at the resting membrane (Em = -60 mV) is calculated, using the Goldman-Hodgkin-Katz equation, to be 3.0 .times. 10-7 cm/s.