Potassium Channel Antagonists and Vascular Reactivity in Stroke-Prone Spontaneously Hypertensive Rats

The goal of this study was to characterize differences in contractile responsiveness to several potassium channel antagonists in vascular smooth muscle from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto normotensive rats (WKY). Helically-cut strips of carotid arteries (endothelium removed) from SHRSP and WKY were mounted in muscle baths for measurement of isometric force generation. Contractile responses to tetraethylammonium (10(-4) to 3 x 10(-2) mol/L) and barium (3 x 10(-5) mol/L), blockers of the voltage-dependent and large conductance, calcium activated potassium channels, were greater in carotid arteries from SHRSP than in those from WKY. In contrast, contractile responses to the voltage-dependent potassium channel blockers 3,4-diamino-pyridine (10(-6) to 3 x 10(-3) mol/L) and sparteine (10(-6) to 3 x 10(-2) mol/L) in arteries from SHRSP did not differ from WKY values. Carotid arteries from SHRSP and WKY did not contract to apamin (10(-9) to 10(-6) mol/L), an antagonist of the small conductance, calcium activated potassium channel. Furthermore, relaxation responses to diazoxide (3 x 10(-4) mol/L), an activator of the ATP-sensitive potassium channel, and subsequent contractions to the ATP-sensitive potassium channel blocker glyburide (10(-8) to 3 x 10(-6) mol/L) in arteries from SHRSP did not differ from WKY values. Carotid artery segments from SHRSP were more sensitive to the contractile effects of elevated potassium than those from WKY. We conclude that altered activity of the large conductance, calcium activated potassium channel may play a role in the increased responsiveness observed in arteries from SHRSP.