DECREASED ATP SENSITIVITY OF A K-MUSCLE RELAXATION IN GENETICALLY HYPERTENSIVE RATS( CHANNEL AND ENHANCED VASCULAR SMOOTH)

Objective: To characterize an ATP-sensitive K+ channel at the single-c hannel and tissue level in the vascular smooth muscle of normotensive and genetically hypertensive rats. Methods: Age- and sex-matched Wista r-Kyoto (WKY) rats and stroke-prone spontaneously hypertensive rats (S HRSP) were used. Patch-clamp single-channel recording was used to meas ure K+ channel activity in dissociated tail artery cells. The effect o f the K+ channel-opener diazoxide and the specific ATP-sensitive K+ ch annel antagonist glyburide on isometric force development in isolated tail artery strips was determined by a standard muscle bath technique. Results: The concentration of ATP that caused half-maximal reduction in channel activity was greater in the SHRSP than in the WKY rats. Tai l artery strips and cells from SHRSP were more sensitive to the effect of diazoxide on relaxation and channel activity, and less responsive to the effect of glyburide, than were those from WKY rats. Conclusions : The decreased ATP sensitivity of this K+ channel may partly compensa te for the increased vascular reactivity in hypertension, and the chan ge in this property of the channel may be responsible for the altered sensitivity to diazoxide and glyburide in SHRSP.