Extracellular Acidification Related to the Stimulation of Catecholamines Release by Strontium in the Bovine Adrenal Medulla

Abstract

The possible modifications of extracellular pH associated with the secretion of catecholamines evoked by the introduction of 2.2 mM Sr2+ to a Ca(2+)-free, buffer-free, Locke solution were investigated in decorticated perfused bovine adrenal glands. A progressive and reversible decrease of external pH accompanied the catecholamine release promoted by Sr(2+)-introduction into the perfusion fluid. This extracellular acid shift was practically undetected when the chromaffin tissue was stimulated by the addition of Sr2+ to a buffered medium. Both the secretory response as well as the extracellular pH drop mediated by Sr(2+)-introduction to a Ca(2+)-free, buffer-free, Locke solution were markedly inhibited by methoxyverapamil (0.3 mM), Mg2+ (20 mM) and hyperosmolarity (750 mOsm). The exposure of the adrenal medulla to a Ca(2+)-free, buffer-free, high-K+ solution containing 2.2 mM Sr2+ for 6 min promoted a significant enhancement of both the secretory response and the acidification of the perfusates compared with the responses evoked by Sr2+ in a 5.6 mM K+ medium. These results are consistent with the existence of a close relationship between extracellular acidification and the release of catecholamines triggered by the introduction of Sr2+ to the perfusion fluid.