Cell Swelling-induced Insulin Secretion from INS-1E Cells is Inhibited by Extracellular Ca2+ and is Tetanus Toxin Resistant

Abstract

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 Ca²⁺ despite a good response to glucose challenge and appropriate increase in cell volume. Surprisingly, perifusion with Ca²⁺-depleted medium showed distinct secretory response of INS-1E cells to hypotonicity. Objective of this study was further characterization of the role of Ca²⁺ in secretory process in INS-1 and INS-1E cell lines. Ca²⁺ depleted hypotonic medium with 10 µM BAPTA/AM (intracellular chelator) induced insulin secretion from both types of cells. We demonstrated expression of L-type Ca²⁺ channel Ca_v1.2 and non-L-type Ca²⁺ channels Ca_v2.1 (P/Q-type), Ca_v2.2 (N-type), and Ca_v3.1 (T-type) in both cell lines. Inhibition of L type channel with nifedipine and/or P/Q type with ω-agatoxin IVA enabled distinct response to hypotonic medium also in INS-1E cells. Tetanus toxin (TeTx) in medium containing Ca²⁺ 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 Ca²⁺, does not require intracellular Ca²⁺ and is TeTx resistant.