Influence of cyclic AMP on intracellular pH regulation and chloride fluxes in barnacle muscle fibres

Abstract

THE pH sensitivity of numerous intracellular processes requires the close regulation of internal pH (pH_i). As the pH_i of many cells is maintained at a higher value than it would have if H⁺ were at equilibrium across the cell membrane, it follows that the acidifying effects of cellular metabolism and of passive H⁺ influx and HCO⁻₃ efflux must be balanced by active acid extrusion. It is now generally accepted that this extrusion is stimulated by decreases in pH_i, and that, in several cells, it is accomplished by exchanging external HCO⁻₃ for internal Cl⁻ (refs 1–4). Recently, a role for cyclic 3′,5′-adenosine monophosphate (cyclic AMP) in pH_i regulation was suggested by the observation that dibutyryl cyclic AMP attenuates the CO₂-induced fall of pH_i in mammalian cardiac muscle⁵. We now report experiments on the effects of cyclic AMP on acid extrusion and on accompanying Cl⁻ fluxes in the barnacle muscle fibre, a preparation known to contain cyclic AMP (ref. 6). Our data show that internally applied cyclic AMP enhances the response of the pH_i-regulating system to acid loads.