Disulfonic Stilbene Derivatives

A BS T R A C T 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. Clhad 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 chloridepermeable channel exists in the squid axon membrane. The chloride permeability (Pci) 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-' cm/s .