Vasomotor response induced by change of extracellular potassium and magnesium in cerebral penetrating arterioles.

We investigated the effects of changing the extracellular potassium as well as magnesium concentration ([K+]₀ and [Mg²+]₀) in cerebral penetrating arterioles. The internal diameter of isolated pressurized cerebral penetrating arterioles in rat was measured under the microscope in the low [K+]₀, low [Mg²+]₀ and high [Mg²+]₀, respectively. Vascular responses induced by the low [K+]₀ were observed in the absence and presence of several inhibitors. The low [K+]₀ produced a biphasic response consisting of an initial transient constriction followed by dilation. The transient constriction was attenuated by Na+-K+-adenosine triphosphatase (ATPase) inhibitor in a concentration-dependent manner and L-type Ca²+ channel inhibitor but not by all K+ channel inhibitors. The low [Mg²+]₀ significantly induced constriction, whereas the high [Mg²+]₀ induced dilation. We analyzed that transient constriction in the low [K+]₀ may be led by membrane depolarization induced by inactivity in Na+-K+-ATPase. The vasomotor responses of the changing of [K+]₀ as well as [Mg²+]₀ in a cerebral microcirculation may influence the pathological and therapeutic condition in cerebrovascular diseases, and may provide new therapeutic targets.