AMILORIDE-SENSITIVE AND HCO3--DEPENDENT ION-TRANSPORT ACTIVATED BY ALDOSTERONE AND VASOTOCIN IN A6 CELLS

We studied the effects of aldosterone (Aldo) and arginine vasotocin (A VT) on ion transport of renal epithelial cell line (A6) by measuring s hort-circuit current (I-sc). AVT induced a rapid, transient increase i n I-sc, followed by a decrease toward the baseline in cells untreated with Aldo. In cells treated with Aldo, I-sc showed a biphasic response to AVT, i.e., both transient and sustained increases over 40 min afte r addition of AVT. The transient increase was composed only of amilori de-insensitive I-sc regardless of Aldo treatment, whereas the sustaine d increase contained both amiloride-sensitive and amiloride-insensitiv e components. The main part of the amiloride-insensitive, sustained I- sc depended on HCO3-. In cells treated with Aldo for 1 day, removal of HCO3- in the bathing solution enhanced the amiloride-sensitive compon ent and decreased the amiloride-insensitive one. These data suggest th at 1) Aldo treatment is necessary for an AVT-induced sustained increas e of I-sc and 2) a HCO3--dependent I-sc mainly contributes to the sust ained increase in amiloride-insensitive I-sc.