Interaction of catecholamine and acetazolamide in the action on the endolymphatic sac direct current potential

Our recent studies have revealed that catecholamines depress the endolymphatic sac DC potential (ESP) by beta-adrenergic action, and that acetazolamide (ACTZ), a potent carbonic anhydrase inhibitor, decreases the ESP. The interaction of ACTZ and isoproterenol (Iso), a nonselective beta agonist, in their action on the ESP was examined in the guinea pig. Intravenous administration of Iso (6.25 micrograms/kg/min) and ACTZ (10 mg/kg) reduced the ESP amplitude by 38.5 +/- 5.9% (n = 8) and 39.8 +/- 3.7% (n = 8), respectively. Co-administration of both agents reduced the ESP amplitude by 62.3 +/- 3.3% (n = 8). The ESP change induced by co-administration was significantly larger than that by the administration of each agent alone. Co-treatment with Iso and ACTZ at doses producing near-maximum reduction of the ESP depressed almost all parts of oxygen-dependent components of the ESP. The results suggest that Iso and ACTZ decrease the ESP via mechanisms different from each other, and that oxygen-dependent components of the ESP are composed of Iso- and ACTZ-sensitive parts.