Desensitization by external na of the cyclic AMP-dependent Na+/H+ antiporter in trout red blood cells

Abstract

The erthrocytes of the trout, Salmo gairdneri, react to fl-adrenergic stimulation by activating a cyclic AMP-dependent and amiloride-sensitire Na+/H+ antiporter (see Borgese, F., F. Garcia-Romeu, and R. Motais, Journal of General Physiology, 1986, 87:551-566). The present study traces the kinetic behavior of the unidirectional Na fluxes after stimulation by isoproterenol. A very considerable increase (100-fold) of the unidirectional Na influx (JinNa), follows the addition of isoproterenol to the erythrocyte suspension. After 1.5 min, JinNa falls suddenly, and asymptotically diminishes toward the nonstimutated flux level. The unidirectional Na effiux (JinNa) proceeds according to similar kinetics. The decrease of JinNa and JinNa is not linked to either a change in the driving forces of the transported ions or a decrease of the cyclic AMP concentration but to a desensitization of the Na+/H+ antiporter. This desensitization is dependent on the external Na concentration and is not controlled by internal Na, cell swelling, or external Ca. © 1988, Rockefeller University Press., All rights reserved.