[The role of G protein in Leu-enkephalin induced Ca2+ release from intracellular pool in myocytes]

The mechanism underlying Leu-enkephalin (LEK) induced increase of the intracellular concentration of free calcium ([Ca2+]i) in rat ventricular myocytes was investigated by using fura-2 AM as a calcium indicator. The results were as follows: LEK (60 mumol/L) elevated [Ca2+]i in ventricular myocytes no matter whether extracellular calcium was removed or not. However, the effect was no longer observed when the calcium in the intracellular pool was depleted by caffeine (5 mmol/L). The LEK effect could also be blocked by naloxone (100 mumol/L), pretreatment of the cells with PTX (200 ng/L) 8-10 h or procain (2 mmol/L). The results suggest that the LEK effect is mediated by coupling of G-protein with delta-receptor that induced Ca2+ release from the intracellular pool in myocytes.