Muscle membranes of the porcine but not guinea-pig mesenteric artery wee hyperpolarized by applications of over 10(-6) M 2-nicotinamidoethyl nitrate (SG 75; 2-NN) dose-dependently from -53 to -72 mV, due to an increase in the ionic conductance of the membrane. In the porcine mesenteric artery but not guinea-pig, 2-NN suppressed the K-induced contraction in concentrations below 20 mM [K]0. The suppression of the K-induced contraction depended on the degree of hyperpolarization and the level of the resting membrane potential. The norepinephrine-induced contraction was suppressed by 2-NN with hyperpolarization of the membrane in the porcine mesenteric artery, but with no change in the membrane potential in the guinea-pig mesenteric artery, presumably due to suppression of the Ca-mobilization in the cell. The excitatory junction potential (ejp) could be recorded by perivascular nerve stimulation in both mesenteric arteries. Whether or not the membrane was hyperpolarized, 2-NN increased the amplitude of ejp in both tissues and increased the appearances of miniature ejp in the guinea-pig mesenteric artery. Nitroglycerin did not modify the membrane potential, the amplitude of ejp, electrical threshold and spike superimposed on the ejp, while sodium nitroprusside suppressed the amplitude of ejp, the facilitation process produced by repetitive stimulation and the spike superimposed on the ejp. Specific features of 2-NN actions on the muscle cell and adrenergic transmission of the mesenteric arteries in both species were discussed in relation to vasodilating actions, species differences and also in relation to other nitrite compounds.