Effects of several antibiotics on the neuromuscular junction: Part II.

The effects of various kinds of antibiotics including tetracycline (TC), chloramphenicol (CP), sodium cephalothin (CET), sodium cefazolin (CEZ), colistin sulfate (CL), colistin sodium methanesulfonate (CL-M), bacitracin (BC), gramicidin HCl (GR), rifampicin sulfate (RFP) and lincomycin (LCM), on the neuromuscular junction (NMJ) were studied by in vitro and in vivo experiments. In in vitro experiments, CL and LCM exhibited a blocking effect on the NMJ in rat phrenic nerve diaphragm preparations, and GR caused a marked increase in muscle contraction. This effect was not affected by administration of eserine or CaCl2. In in vitro experiments with frog sciatica nerve and musculus sartorius preparations, CL and GR induced the appearance of endplate potentials, suggesting blockade of the NMJ. No blocking effect of other antibiotics was observed. In in vitro experiments with the preparations from Rana catesbiana frogs, TC and LCM induced a decrease in the frequency of miniature endplate potentials. In in vivo experiments with rabbit musculus tibialis anterior preparations, CL, TC and LCM exerted a blocking effect soon after administration, but GR and RFP had a late blocking effect. CL, GR, BC and RFP were found not to compete with eserine or CaCl2 in terms of the blocking effect on the NMJ. From the fact that TC did not compete with eserine but did compete with CaCl2 and with KCl as blockers at the NMJ, this blocking effect of TC seems to be due to inhibition of release of acetylcholine (ACh). The fact that LCM competes with eserine indicates that this antibiotic has the same type of action as curare on ACh receptors of the NMJ.(ABSTRACT TRUNCATED AT 250 WORDS)