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 Langerhans in the absence of glucose or extracellular calcium. We also found that the anesthetic evokes a dose-dependent rise of the intracellular free-calcium 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 Ca(2+)-deficient medium (< 1 microM) or elevated [K+]o. Furthermore, tetracaine (> or = 300 microM) depolarized the beta-cell membrane in mouse pancreatic islets, but inhibited Ca2+ entry through voltage-gated Ca2+ channels in HIT cells, an insulin-secreting cell line. From these data we conclude that tetracaine-enhancement of insulin release occurs by mechanisms that are independent of Ca2+ entry across the cell membrane. The tetracaine-induced [Ca2+]i rise in cultured rat beta-cells and insulin secretion from mouse islets is insensitive to dantrolene (20 microM), a drug that inhibits Ca2+ release evoked by cholinergic agonists in the pancreatic beta-cell, and thapsigargin (3 microM), a blocker of the endoplasmic reticulum (ER) Ca2+ pump. We conclude that the Ca2+ required for tetracaine-potentiated insulin secretion is released from intracellular Ca2+ stores other than the ER. Furthermore, tetracaine-induced Ca2+ release was unaffected by the mitochondrial electron transfer inhibitors NaN3 and rotenone. Taken together, these data show that a calcium source other than the ER and mitochondria can affect beta-cell insulin secretion.
Mears
D
D
Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, USA.
Leighton
X
X
Atwater
I
I
Rojas
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D004721:Endoplasmic Reticulum; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007424:Intracellular Fluid; D015640:Ion Channel Gating; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria; D051381:Rats; D017208:Rats, Wistar; D013748:Tetracaine / Q000378:metabolism / Q000494:pharmacology
D015220:Calcium Channels; D007328:Insulin; D013748:Tetracaine; D002118:Calcium