ABSTRACT
UNLABELLED: Cell swelling-induced insulin secretion represents an alternative pathway of stimulation of insulin secretion. INS-1E rat tumor beta cells do not release insulin in response to cell swelling in presence of Ca(2+) despite a good response to glucose challenge and appropriate increase in cell volume. Surprisingly, perifusion with Ca(2+)-depleted medium showed distinct secretory response of INS-1E cells to hypotonicity. Objective of this study was further characterization of the role of Ca(2+) in secretory process in INS-1 and INS-1E cell lines. Ca(2+) depleted hypotonic medium with 10 muM BAPTA/AM (intracellular chelator) induced insulin secretion from both types of cells. We demonstrated expression of L-type Ca(2+) channel Ca(v)1.2 and non-L-type Ca(2+) channels Ca(v)2.1 (P/Q-type), Ca(v)2.2 (N-type), and Ca(v)3.1 (T-type) in both cell lines. Inhibition of L type channel with nifedipine and/or P/Q type with omega-agatoxin IVA enabled distinct response to hypotonic medium also in INS-1E cells. Tetanus toxin (TeTx) in medium containing Ca(2+) and a group of calcium channel blockers inhibited hypotonicity-induced insulin secretion from INS-1 cells but not from INS-1E cells. CONCLUSION: Hypotonicity-induced insulin secretion from INS-1E cells is inhibited by extracellular Ca(2+), does not require intracellular Ca(2+) and is TeTx resistant.
