Potassium channels and vascular reactivity in genetically hypertensive rats

In hypertension, membrane potassium permeability and vascular reactivity are increased. This study characterizes a potassium-selective channel and contractions to barium, a potassium channel inhibitor, in vascular smooth muscle (tail artery) from spontaneously hypertensive stroke-prone rats (SHRSP) and normotensive Wistar-Kyoto (WKY) rats. Smooth muscle cells were isolated by enzymatic digestion, and potassium channel activity was characterized by using patch-clamp technique (inside-out configuration). Isometric contractile activity was evaluated in helically cut arterial strips by using standard muscle bath methodology. In membrane patches, a voltage-gated, calcium-insensitive, potassium-selective channel of large conductance (200 picosiemens) was observed. The channel did not conduct sodium or rubidium. Barium (10(-6) to 10(-4) M) produced a dose-dependent blockade of channel activity. These channel characteristics did not differ in SHRSP and WKY rat cells. After treatment with 35 mM KCl, barium (10(-5) to 10(-3) M) caused greater contractions in SHRSP arteries compared with arteries in WKY rats. The contractions to barium were markedly attenuated in calcium-free solution, and nifedipine and verapamil abolished contractions induced by barium in depolarizing solution. We conclude that increased vascular reactivity to barium in SHRSP arteries is not due to an alteration in the biophysical properties of the potassium channel studied.