The purpose of this study was to test the hypothesis that differential autoregulation of cerebral and hindquarter arteries during simulated microgravity is mediated or modulated by differential activation of potassium channels in vascular smooth muscle cells (VSMCs) of arteries in different anatomic regions. Sprague-Dawley rats were subjected to 1-wk and 4-wk tail-suspension to simulate the cardiovascular deconditioning effect due to short- and medium-term microgravity. Potassium channel function of VSMCs was studied by pharmacologic method and patch clamp technique. The BK_Ca and Kv currents were determined by subtracting the current recorded after applications of 1 mM TEA and 1 mM TEA + 3 mM 4-AP, respectively, from that of before. For cerebral vessels, the normalized contractility of basilar arterial rings to TEA, a BK_Ca blocker, and 4-AP, a Kv blocker, was significantly decreased after 1-wk and 4-wk simulated microgravity, respectively. The VSMCs isolated from the middle cerebral artery branches of suspended rats had a more depolarized membrane potential (Em) and a smaller potassium current density as compared with those of control rats. Furthermore, the reduced total current density was due to a smaller BKca and a smaller Kv current density in cerebral VSMCs after 1-wk and 4-wk tail-suspension, respectively. For hindquarter vessels, VSMCs isolated from the 2nd -6th order small mesenteric arteries of both 1- and 4-wk suspended rats had a more negative Em and larger potassium current densities for total, BKca, and Kv currents. These results indicate that differential activation of potassium channels occur in cerebral and hindquarter VSMCs during short- and medium-term simulated microgravity. It is further suggested that different profiles of channel remodeling might occur in VSMCs as one of the important underlying cellular mechanisms to mediate and modulate differential vascular adaptation during microgravity.