CYCLIC-AMP-INDUCED WATER-UPTAKE IN A MOTH OVARY - INHIBITION BY BAFILOMYCIN AND ANTHRACENE-9-CARBOXYLIC ACID

The ion physiology of osmotic swelling and a consequent loss of epithe lial patency was examined in the ovaries of the moth Hyalophora cecrop ia, After 30 min in the presence of an activator of cyclic-AMP-depende nt protein kinase (PKA), the membrane potentials of both oocyte and fo llicle cells had hyperpolarized by approximately 30%, cytoplasmic pH h ad dropped from 7.26 to 7.06, a normally Low Cl- conductance had incre ased and the follicle cells had begun to swell. Since ion distribution studies have indicated that conductance increases should depolarize m embranes in this system, it is proposed that hyperpolarization may be effected by an azide-inhibitable component of the membrane potential. Nanomolar levels of bafilomycin, an inhibitor of H+ V-ATPase, blocked the active component and prevented osmotic swelling in response to PKA activation. Under a variety of circumstances, correlations were seen between membrane potential and cytoplasmic pH, suggesting that substra te availability to the proton pump may contribute to hyperpolarization , H+ V-ATPases are known to energize ion and water transport across ma ny epithelia, but in this case they generate water absorption by the e pithelium. The increase in Cl- conductance was also required for the s welling response: the Cl- channel blocker anthracene-9-carboxylic acid prevented both swelling and hyperpolarization, as did Cl- substitutio n in the medium. Differences in isotope loading rates between (36)Cl(- )and Rb-86(+) suggested that, after PKA activation, Cl- functions oth er than as a counterion for K+ uptake.