Temperature dependence of catecholamine secretion from cultured bovine chromaffin cells

Secretion of both epinephrine and norepinephrine by cultured chromaffin cells was studied at temperatures ranging from 0 degrees C to 37 degrees C. The percentage of epinephrine secreted was always lower than that of norepinephrine when the cells were stimulated with either acetylcholine or high K+ at any temperature. When the cells were stimulated with acetylcholine or carbachol the percentage of catecholamine secreted at 10 min increased with temperature from 4 degrees C to 24 degrees C and then decreased from 24 degrees C to 37 degrees C. Potassium-stimulated cells secreted increasing amounts of catecholamine as the temperature was increased to 37 degrees C. We found, however, that the initial rates of secretion increased continuously as temperature increased throughout the range for both carbachol- and K+-stimulated cells. The temperature maximum of acetylcholine-stimulated secretion is caused by a faster shut-off of secretion at higher temperature. The Arrhenius plots of initial rates show an inflection point at approximately 17 degrees C for carbachol-stimulated cells. The plot for K+-stimulated cells is a straight line over the entire temperature range. The transition could be caused by a conformational change in the cholinergic receptor/ion channel molecule.