Electrolyte transport by alkaline gland of little skate Raja erinacea

Abstract

Transepithelial flux studies and conventional intracellular microelectrode measurements were employed to examine the mechanisms of ion transport by the alkaline gland of the male skate, Raja erinacea. These studies reveal that the transepithelial potential is 6.9 +/- 0.6 mV, lumen reference, and that the transepithelial resistance is 140 omega . cm2. The short-circuit current across this epithelium is entirely accounted for by net secretion of Cl, whereas transepithelial active transport of Na does not appear to be present in this tissue. Cl secretion and/or short-circuit current are reduced by serosal furosemide and abolished when the bathing solution Na is replaced with choline or when ouabain is added to the serosal bathing solution. Intracellular microelectrode studies reveal that the apical membrane potential is -43 mV, cell interior negative to the mucosal bathing solution. The transepithelial resistance in these tissues was 103 +/- 12 omega . cm2 and the apparent fractional resistance, i.e., the ratio of the change in apical membrane potential to the change in transepithelial potential produced by passing current across the epithelium was 0.39 +/- 0.09. Ion substitution experiments demonstrated that the apical membrane is dominated by a large Cl conductance while the basolateral membrane contains a barium-sensitive potassium conductance. These results suggest that the mechanism of Cl secretion by the alkaline gland is similar to the mechanism described for a variety of Cl secretory epithelia.