DIFFERENT MODULATION OF CA-ACTIVATED K-CHANNELS BY THE INTRACELLULAR REDOX POTENTIAL IN PULMONARY AND EAR ARTERIAL SMOOTH-MUSCLE CELLS OF THE RABBIT

We investigated the electrical responses of Ca-activated K (KCa) curre nts induced by hypoxia and reduction of oxidation of the channel prote in in pulmonary (PASMC) and ear (EASMC) arterial smooth muscle cells u sing the patch-clamp technique. In cell-attached patches, in the prese nce of a high K solution (containing 0.316 mu M Ca2+), the activity of K-Ca channels from PASMC was decreased (by 49 +/- 7% compared to cont rol pipette potential = -70 MV) by changing to a hypoxic solution (1 m M Na2S2O4, aeration with 100% N-2 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 appli ed redox couples to the intracellular side. Reducing agents, such as d ithiothreitol (DDT, 5mM), reduced glutathione, (GSH, 5 mM), and nicoti namide 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 KCa channel activity in both PAS MC and EASMC. The increased activity due to oxidizing agents was resto red by applying reducing agents. From these results, we could suggest that the basal redox state of 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 an d EASMC K-Ca channels to hypoxia.