The inhibition of K⁺-secretory response by caffeine in bovine chromaffin cells is time dependent

Catecholamine secretion was studied using cultures of bovine chromaffin cells. Secretory response induced by K⁺ (50 mM) was inhibited 62% by 50 mM caffeine, when both stimulators were added together. Preincubation with caffeine, 50 mM, decreased the catecholamines release stimulated by potassium. The effect was time-dependent and reached 90% of inhibition when the cells were exposed previously to caffeine for more than 5 min. ⁴⁵Ca uptake was not affected by the simultaneous challenge with potassium and caffeine. However 5 min of preincubation with caffeine decreased 50% of radioactive uptake in chromaffin cells stimulated by potassium. These results indicate that caffeine inhibits the K⁺-secretory response in bovine chromaffin cells through a time-dependent mechanism which blocks the Ca²⁺ influx. This may be due to interaction with the intracellular calcium buffer system.