Protein kinase C-dependent inhibition of BKCa current in rat aorta smooth muscle cells following γ-irradiation

Abstract

Purpose: The aim of this study was to estimate the effects of non-fatal whole-body γ-irradiation on outward potassium plasma membrane conductivity in rat vascular smooth muscle cells (VSMC), and to identify underlying mechanisms.Materials and methods: Rats were exposed to a 6 Gy dose irradiation from a cobalt60 source. Whole-cell potassium current was measured in freshly isolated rat aorta smooth muscle cells using standard patch-clamp technique.Results: We have determined that whole-body ionising irradiation significantly inhibits whole-cell outward K+ current in rat aortic VSMC obtained from irradiated rats 9 and 30 days after irradiation, and this inhibition appears to be increased throughout post-irradiation period. Using selective inhibitors of small conductance Ca2+-activated K+ channels (SKCa), apamin (1 μM), intermediate conductance Ca2+-activated K+ channels (IKCa,), charybdotoxin (1 μM) and a large conductance Ca2+-activated K+ channels (BKCa), paxilline (500 nM), we established that the main component of whole-cell outward K+ current in rat aortic VSMC is due to BKCa. It is clear that on the 9th day after irradiation paxilline had only a small effect on whole-cell outward K+ current in VSMC, and was without effect on the 30th day post-irradiation, suggesting complete suppression of the BKCa current. The PKC inhibitor, chelerythrine (100 nM), effectively reversed the suppression of whole-cell outward K+ current induced by ionising irradiation in the post-irradiation period of 9 and 30 days.Conclusions: The results suggest that irradiation-evoked inhibition of the BKCa current in aortic VSMC is mediated by PKC. Taken together, our data indicate that one of the mechanisms leading to elevation of vascular tone and related arterial hypertension development under ionising irradiation impact is a PKC-mediated inhibition of BKCa channels in VSMC.