The effects of gentamicin on tension responses to norepinephrine and KCl and Ca++ binding and fluxes in canine renal vein.

The relaxant and inhibitory actions of gentamicin (Gent) on norepinephrine (NE)- and KCl-induced maximal contractions were delineated in canine renal vein, and subsequently correlated with Gent-induced effects on 45Ca uptake and efflux. Gent is a more potent inhibitor than a relaxant of KCl-induced contractions, whereas the opposite relationship exists for NE-induced contractions. Gent extensively inhibits (100%) or relaxes (82%) KCl-induced contractions. Prior exposure to Gent depresses NE-induced contractions by 68% and changes the response from a maintained to a phasic one. The initial, rapid upstroke is decreased in rat and magnitude. Maximum NE-induced contractions are rapidly relaxed (78%) by Gent. Gent is rinsed out more rapidly than NE, resulting in a secondary, transient contraction, which is concentration-dependent and only partially inhibited by D 600. Gent increases efflux into a 0 Ca++ solution in a maintained manner. Ca++ binding at La+++-sensitive and La+++-insensitive sites exhibiting high or low affinity characteristics are decreased appreciably (30-49%) by Gent. The high degree of sensitivity of canine renal vein to Gent results from Gent-induced effects on superficial membrane Ca++ binding sites, which are of significant importance in excitation/contraction (relaxation) coupling in venous smooth muscle.