Catecholamine uptake and release in isolated chromaffin granules exposed to halothane

The effects of halothane on the catecholamine release from chromaffin granules and the uptake of 14C-epinephrine into the granules were studied using isolated bovine adrenal medullary chromaffin granules. The granules were isolated with a Millipore filter, and were incubated for 10 min in an isotonic medium containing adenosine triphosphate (ATP)-Mg++. At halothane concentration of 0.4 mM or greater, the uptake of 14C-epinephrine into the granules was inhibited in a dose-related manner. At 0.7 mM halothane, epinephrine uptake was reduced to 56 per cent of control. The inhibition was completely reversible after removal of halothane from the medium. The inhibitory effect of halothane was not affected by high-osmolar medium. Catecholamine release from isolated chromaffin granules was enhanced by halothane at concentrations of more than 1.3 mM, but was not affected when the concentration was 0.7 mM or less. The results suggest the possiblity that halothane might alter the intracellular storage-turnover process and the subsequent release pattern of catecholamines. The possible mechanisms of this action are discussed.