Direct myocardial depressant effects of gentamicin.

Effects of gentamicin on myocardial contractile performance were examined in isolated, electrically driven, rat left atria. This aminoglycoside antibiotic produced a maintained and concentration-dependent (0.0156-0.25 mM) depression of myocardial contractile tension that was reversible by replacing the incubation media with gentamicin-free solution. Time to peak tension and total contraction time were not discernibly altered by gentamicin. The negative inotropic response elicited by gentamicin was antagonized in a competivitive-like manner by increasing the calcium ion (Ca2+) concentration of the bathing solution, whereas, the depressant effects of gentamicin were antagonized by norepinephrine in a non-competitive-like manner. Present findings demonstrate a direct negative inotropic effect of gentamicin and suggest that this antibiotic interferes with the participation of Ca2+ in the events leading to mecahnical activity of atrial myocardium.