title: Effect of hydralazine on tension and membrane potential in the rat caudal artery.
abstract: To determine whether the vasodilator, hydralazine (HYD), produces hyperpolarization of vascular muscle cells, we measured the effect of HYD on membrane potential and contractile responses to phenylephrine and K+. HYD (1 microM) caused a 4 mV hyperpolarization of phenylephrine-depolarized arteries (compared with controls without HYD), which could possibly account for up to three-fourths of the 39% decrease in tension measured. K+-contracted vessels were also 34% relaxed by 1 microM HYD without an effect on membrane potential. In addition, HYD further relaxed phenylephrine-stimulated vessels previously relaxed by D-600, suggesting that Ca++ channel blockade may not be an important mechanism of vasodilation for HYD. The evidence suggests that a nonmembrane action of HYD on arterial muscle probably multiplies the relaxant effect of membrane potential hyperpolarization. Both mechanisms would attenuate the effects of adrenergic stimulation.
mesh_terms: D000818:Animals; D001158:Arteries / Q000187:drug effects; D006830:Hydralazine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013268:Stimulation, Chemical
chemical_list: D010656:Phenylephrine; D006830:Hydralazine; D011188:Potassium