OBJECTIVE: To elucidate the mechanism of vascular hyporeactivity following severe hemorrhagic shock (HS) by studying the changes of ATP-sensitive potassium channels' (K(ATP)) properties and membrane potential of mesenteric arteriolar smooth muscle cells. METHODS: Single channel currents were studied on cell-attached and inside-out patches of enzymatically isolated mesenteric arteriolar smooth muscle cells (ASMCs). Membrane potentials of arteriolar strips and ASMCs were recorded by intracellular membrane potential recording method and confocal microscopy, respectively. RESULTS: K(ATP) channels in ASMCs were activated, which induced smooth muscle hyperpolarization following vascular hyporeactivity in HS. CONCLUSIONS: Hyperpolarizing effect of K(ATP) channel activation plays an important role in low vasoreactivity during severe hemorrhagic shock.