Tetracaine stimulates insulin secretion from the pancreatic beta-cell by release of intracellular calcium

The role of intracellular calcium stores in stimulus-secretion coupling in the pancreatic beta-cell is largely unknown. We report here that tetracaine stimulates insulin secretion from collagenase-isolated mouse islets of Lan gerhans in the absence of glucose or extracellular calcium. We also found t hat the anesthetic evokes a dose-dependent rise of the intracellular free-c alcium concentration ([Ca2+](i)) in cultured rat and mouse beta-cells. The tetracaine-specific [Ca2+]i rise also occurs in the absence of glucose, or in beta-cells depolarized by exposure to a Ca2+-deficient medium (<1 mu M) or elevated [K+](o). Furthermore, tetracaine (greater than or equal to 300 mu M) depolarized the beta-cell membrane in mouse pancreatic islets, but in hibited Ca2+ entry through voltage-gated Ca2+ channels in HIT cells, an ins ulin-secreting cell line. From these data we conclude that tetracaine-enhan cement of insulin release occurs by mechanisms that are independent of Ca2 entry across the cell membrane. The tetracaine-induced [Ca2+], rise in cul tured rat beta-cells and insulin secretion from mouse islets is insensitive to dantrolene (20 mu M), a drug that inhibits Ca2+ release evoked by choli nergic agonists in the pancreatic beta-cell, and thapsigargin (3 mu M), a b locker of the endoplasmic reticulum (ER) Ca2+ pump. We conclude that the Ca 2+ required for tetracaine-potentiated insulin secretion is released from i ntracellular Ca2+ stores other than the ER. Furthermore, tetracaine-induced Ca2+ release was unaffected by the mitochondrial electron transfer inhibit ors NaN3 and rotenone. Taken together, these data show that a calcium sourc e other than the ER and mitochondria can affect beta-cell insulin secretion .