Possible postsynaptic action of aminoglycosides in the frog rectus abdominis

The present study was undertaken to investigate the postsynaptic effects of aminoglycosides on contractions evoked by acetylcholine (ACh), KCl, electr ical field stimulation (EFS) and Na+-and Ca2+-free Ringer solution with 0.2 mM Na-2 EDTA (NaFCaFR) in the isolated frog rectus abdominis. Neomycin inh ibited contraction elicited by ACh, NaFCaFR, and EFS at the higher frequenc ies (8 and 10 Hz) but not those elicited by KCI and EFS at the lower freque ncies (2, 3 and 5 Hz). D-tubocurarine inhibited ACh-induced contractions in a concentration-dependent manner. In addition, drug reduced EFS-evoked con tractions to a limited extent. Lower concentrations (10(-5), 5x10(-5), 10(- 4), 2x10(-4) and 3 x 10(-4) M) but not higher concentrations (4 x 10(-4) an d 5 x 10(-4) M) of methoxyverapamil exhibited a concentration-dependent inh ibitory action on Na, Ca, R-induced contractions. Similar inhibitions of th e same type of contraction were displayed by aminoglycosides (neomycin, str eptomycin, netilmycin, gentamycin and amikacin). These results suggest that in addition to their antagonistic action on nicotinic receptors in the fro g rectus abdominis, aminoglycosides may exert stabilizing effects on some f unctional components contributing to contractions at the membrane.