Abstract
Using a direct cellular micropuncture technique with double-barreled ion-selective microelectrodes, we investigated the effect of dibutyryl-cyclic AMP (db-cAMP) on the membrane potential and the transport of Na+, K+, and H+ in doubly-perfused bullfrog proximal tubules. The peritubular membrane potential difference (EM) and the intracellular K+, Na+ activities ((K)i, (Na)i) or intracellular and luminal pH were monitored continuously after peritubular administration of db-cAMP (10-3-10-4M). Results: 1) db-cAMP hyperpolarized the EM by 8.0mV with an increase of (K)i by 4.8mEq/l; 2) the peritubular administration of high K+ (13.5 and 50mM) solutions depolarized the EM by 11.5 and 41.5mV, respectively. The high K+ perfusate with db-cAMP produced a depolarization to the same level as that in simple high K+ perfusion without db-cAMP; 3) db-cAMP transiently blocked the luminal acidification concomitantly with a cellular alkalinization by about 0.1 pH; and 4) db-cAMP caused a decrease of (Na)i by 5.0mEq/l. Conclusions: 1) cAMP causes an increase of K+ permeability in the peritubular membrane; 2) cAMP induces a cytosol alkalosis by enhancing incorporation of H+ into the subcellular vesicles, thus favoring the activation of Na+/K+ pump; and 3) cAMP, in effect, suppresses the Na+/H+ exchange mechanism in the luminal membrane and transiently blocks the proximal urinary acidification.
