Functional coupling between ‘R‐type’ Ca 2+ channels and insulin secretion in the insulinoma cell line INS‐1

Among voltage‐gated Ca 2+ channels the non‐dihydropyridine‐sensitive α1E subunit is functionally less well characterized than the structurally related α1A (ω‐agatoxin‐IVA sensitive, P‐ /Q‐type) and α1B (ω‐conotoxin‐GVIA sensitive, N‐type) subunits. In the rat insulinoma cell line, INS‐1, a tissue‐specific splice variant of α1E (α1Ee) has been characterized at the mRNA and protein levels, suggesting that INS‐1 cells are a suitable model for investigating the function of α1Ee. In α1E‐transfected human embryonic kidney (HEK‐293) cells the α1E‐selective peptide antagonist SNX‐482 (100 n m ) reduces α1Ed‐ and α1Ee‐induced Ba 2+ inward currents in the absence and presence of the auxiliary subunits β3 and α2δ‐2 by more than 80%. The inhibition is fast and only partially reversible. No effect of SNX‐482 was detected on the recombinant T‐type Ca 2+ channel subunits α1G, α1H, and α1I showing that the toxin from the venom of Hysterocrates gigas is useful as an α1E‐selective antagonist. After blocking known components of Ca 2+ channel inward current in INS‐1 cells by 2 µ m (+/–)‐isradipine plus 0.5 µ m ω‐conotoxin‐MVIIC, the remaining current is reduced by 100 n m SNX‐482 from −12.4 ± 1.2 pA/pF to −7.6 ± 0.5 pA/pF ( n  = 9). Furthermore, in INS‐1 cells, glucose‐ and KCl‐induced insulin release are reduced by SNX‐482 in a dose‐dependent manner leading to the conclusion that α1E, in addition to L‐type and non‐L‐type (α1A‐mediated) Ca 2+ currents, is involved in Ca 2+ dependent insulin secretion of INS‐1 cells.