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

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 was found to become 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. On the basis of these experimental results, it is concluded that 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 X 10(-7) cm/s.