ω-Conotoxin-sensitive, voltage-operated Ca2+ channels in insulin-secreting cells

Down‐regulation of non‐L‐, non‐N‐type (Q‐like) Ca2+ channels by Lambert‐Eaton myasthenic syndrome (LEMS) antibodies in rat insulinoma RINm5F cells

“…Of the three high-voltage-activated (HVA) Ca2+-channel subtypes identified in RINmSF cells (N-, L-type and Q-like) [15], the N-type contributes only a minor proportion of total Ba2+ currents (lO_15%) [17,19]. Its presence complicated the separation of the two other HVA channel currents; therefore, all the effects of LEMS IgGs described here were tested on RINmSF cells pre-treated with 3.2 p,M o-CTx-GVIA (15 min in 2 mM Ca2+) which abolished N-type channel activity.…”

Noradrenaline inhibition of Ca2+ channels and secretion in single patch‐clamped insulinoma cells

“…The remaining VOCCs (Q-like, [29]) are less sensitive to noradrenaline [8]. While the role of the Qlike VOCCs in the control of secretion from RINm5F cells is still unknown, both N-and L-type VOCCs have been shown to be involved in this process, the L-type being the more relevant [30,31]. The finding that noradrenaline has more potent actions on exocytosis than on Ica could be due to the fact that noradrenaline targets the few VOCCs 'crucially' involved in secretion, a role apparently played by L-type VOCC in both adrenal chromaffin [32] and pancreatic beta [33] cells.…”

A single non-L-, non-N-type Ca2+ channel in rat insulin-secreting RINm5F cells

“…-CTx-GVIA (Bachem, Bubendorf, Switzerland) was dissolved in distilled water and frozen at 920°C. To maximize its blocking action, the toxin was dissolved in a standard Tyrode solution (mM): 150 NaCl, 4 KCl, 2 MgCl 2 , 2 CaCl 2 , 10 glucose and 10 HEPES and applied for 1-2 min to block irreversibly the N-type channel [31].…”

“…When acutely applied to the cell, -CTx-GVIA was delivered through a separate glass pipette kept out of the bath and moved close to the cell immediately before toxin application. Due to the slow washing out of the toxin in 100 mM Ba 2+ solutions [12,31], the dish was changed after each cell recording.…”

“…The latter contributes to most of the Ca 2+ current and is ubiquitous in all insulin-secreting cells [2]. Recent reports, however, have provided increasing evidence for the existence, in -cells and -cell lines, of a significant DHP-resistant HVA current component [13,25] that is partially blocked by -CTx-GVIA [31] and modulated by noradrenaline [25]. Electrophysiological [18] and molecular biology studies [15] have also provided evidence for the existence in rat islets and RINm5F cells of a class A Ca 2+ channel (Q-, or P-type) that is resistant to DHP, -CTx-GVIA and high doses of -agatoxin-IVA ( -Aga-IVA), but is sensitive to micromolar concentrations of -CTx-MVIIC.…”