FUNCTIONAL-ROLE OF CA-2+-ACTIVATED K plus CHANNELS IN RESTING STATE OF CAROTID ARTERIES FROM SHR

Carotid arteries from spontaneously hypertensive rats (SHR) exhibited an active tone when exposed to a physiological salt solution; that is, the tension decreased when nifedipine was added. To determine the possible role of Ca2+-activated K+ (K(Ca)) channels in the resting state of these arteries, the effects of agents that interact with these channels on tension and Rb-86 efflux were compared in endothelium-denuded strips of carotid arteries from SHR and normotensive Wistar-Kyoto rats (WKY). The addition of charybdotoxin, a blocker of high-conductance K(Ca) channels, to the resting strips produced a concentration-dependent contraction in SHR but not in WKY. In resting strips preloaded with Rb-86, the basal Rb-86 efflux rate constant was significantly greater in SHR than in WKY. The addition of nifedipine to the resting strips decreased the basal Rb-86 efflux rate constant only in SHR. The effect of nifedipine on tension and Rb-86 efflux in 25.9 mM K+-contracted strips of WKY was comparable to the effect of this blocker in the resting strips of SHR. The basal Ca-45 influx in resting strips of SHR was significantly increased when compared with WKY, and this increase in SHR was abolished by nifedipine. These results suggest that the transmembrane Ca2+ influx via L-type voltage-dependent Ca2+ channels was significantly increased in the resting state of carotid arteries from SHR and that the K(Ca) channels were highly activated.