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We determined lung vascular responses to voltage-gated Ca2+ channel potentiation with BAY K 8644 (BAY). We anesthetized 46 rats (Sprague-Dawley; halothane and pentobarbital) and then excised and perfused their lungs at constant blood flow of 25 +/- 2 (SE) ml.kg-1.min-1 at constant airway and left atrial pressures of 5 and 6 cmH2O, respectively. Pulmonary arterial pressure (Ppa) increased from 13.3 +/- 0.3 cmH2O at baseline to 17.3 +/- 1.3 cmH2O after BAY (2.8 x 10(-6) M; n = 5; P less than 0.01). As determined by micropuncture, arteriolar and venular (Pven) pressures did not change. Increase of perfusate Ca2+ (16 x 10(-3) M; n = 8) similarly increased Ppa. NG-mono-methyl-L-arginine (2 x 10(-4) M), an inhibitor of endothelium-derived relaxing factor, augmented the pressor effect of BAY when given after (n = 4) but not before (n = 4) BAY (P less than 0.01). Prior cyclooxygenase blockade with indomethacin (5 mg/kg; n = 5) attenuated the Ppa response to BAY (P less than 0.01). None of these agents changed Pven. To confirm vasoactivity in veins, we induced smooth muscle depolarization with KCl (20 x 10(-3) M; n = 6) and receptor-mediated responses with histamine (3 x 10(-4) M; n = 7). Both of these agents increased Pven markedly (P less than 0.01). We interpret that, in rat lung, BAY causes arterial but not venous constriction, because the venous segment differs from the arterial with regard to Ca2+ channel potentiation.

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