Reduced glutathione inhibits β-NAD⁺-activated non-selective cation currents in the CRI-G1 rat insulin-secreting cell line

1. Whole-cell voltage-clamp recordings were used to study the characteristics of a non-selective cation current, activated by intracellular ß-NAD⁺, present in CRI-G1 insulin-secreting cells. The monovalent cations Na⁺, K⁺ and Cs⁺ were equally permeant through this channel. 2. The magnitude of the ß-NAD⁺ current was dependent on the concentration of both ß-NAD⁺ and Ca²⁺ in the cell. The properties of the ß-NAD⁺-activated macroscopic current are similar to those of the ß-NAD⁺-activated non-selective cation channel (NS_NAD) examined at the single channel level in this cell line. 3. The presence of intracellular reduced glutathione (GSH) inhibited the ß-NAD⁺-activated macroscopic current and the activity of the NS_NAD channel in inside-out patch recordings. 4. The inhibition of ß-NAD⁺-activated currents by GSH is mimicked by its analogue ophthalmic acid but not by another thiol reducing agent dithiothreitol, indicating the presence of a specific GSH binding site present on the NS_NAD channel or associated protein.