Vascular smooth muscle (VSM) transmembrane potentials (Em) were measured in situ in small branch arteries (150-300-microns o.d.), small branch veins (300-400-microns o.d.), arterioles (90-150-microns o.d.), and venules (80-250-microns o.d.) in the mesenteric and gracilis muscle and the arterioles and venules of cremaster muscle vascular beds in anesthetized rats with reduced renal mass hypertension (HT-RRM) and normotensive sham-operated RRM control rats. All rats were given a 4% NaCl diet for 2 weeks with water ad libitum. Relative to sham, HT-RRM mesenteric and gracilis arterial and venous vessels, but not the microvessels of the cremaster muscle bed, were less polarized during superfusion with normal physiological salt solution. Also relative to sham, hyperpolarization responses to local sympathetic neural (SNS) denervation with 6-hydroxydopamine were greater in mesenteric and gracilis small arteries, arterioles, veins, and venules but not in cremaster microvessels. The immediate (less than 5-minute) electrogenic depolarization response to local blockade of VSM Na(+)-K+ pump activity with 10(-3) M ouabain was similar between each respective HT-RRM and sham vessel pair in each vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)