Different modulation of Ca-activated K channels by the intracellular redox potential in pulmonary and ear arterial smooth muscle cells of the rabbit

Astract

We investigated the electrical responses of Ca-activated K (KCa) currents induced by hypoxia and reduction or oxidation of the channel protein in pulmonary (PASMC) and ear (EASMC) arterial smooth muscle cells using the patch-clamp technique. In cell-attached patches, in the presence of a high K solution (containing 0.316 (μM Ca²⁺), the activity of K_Ca channels from PASMC was decreased (by 49±7% compared to control, pipette potential = −70 mV) by changing to a hypoxic solution (1 mM Na₂S₂O₄, aeration with 100% N₂ gas). EASMC channels did not respond to hypoxia. In order to investigate the possible mechanisms involved, using inside-out patches bathed symmetrically in 150 mM KCl, we applied redox couples to the intracellular side. Reducing agents, such as dithiothreitol (DDT, 5 mM), reduced glutathione, (GSH, 5 mM), and nicotinamide adenine dinucleotide reduced (NADH, 2 mM) decreased PASMC, but not EASMC, K_Ca channel activity. However, oxidizing agents such as 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB, 1 mM), oxidized glutathione (GSSG, 5 mM) and NAD (2 mM) increased K_Ca channel activity in both PASMC and EASMC. The increased activity due to oxidizing agents was restored by applying reducing agents. From these results, we could suggest that the basal redox state of the EASMC K_Ca channel is more reduced than that of the PASMC channel, since the response of K_Ca channels of the EASMC to intracellular reducing agents differs from that of the PASMC. This difference may be related to the different responses of PASMC and EASMC K_Ca channels to hypoxia.