Anion conductances of the giant axon of squid Sepioteuthis

Anion conductances of giant axons of squid, Sepioteuthis, were measured. The axons were internally perfused with a 100-mM tetraethylammonium-phosphate solution and immersed in a 100-mM Ca-salt solution (or Mg-salt solution) containing 0.3 microns tetrodotoxin. The external anion composition was changed. The membrane currents had a large amount of outward rectification due to anion influx across Cl- channels of the membrane (Inoue, 1985). The amount of outward rectification depended on the species of anion used and was strongly influenced by temperature and internal pH. In contrast to the anion conductances themselves, the conductance relative to Cl- (gA/gCl) was found to be quite stable against changes in the membrane potential, temperature, and pH. It is therefore suggested that each gA/gCl is an intrinsic quantity of the Cl- channel of the squid axon membrane. The sequence and values of gA/gCl obtained in this study were NO3- (1.80) greater than I- (1.40) greater than Br- (1.07) greater than Cl- (1.00) greater than MeSO3- (0.46) greater than H2PO2- (0.33) greater than CH3COO- (0.29) greater than SO4(2-) (0.06).