Dual effect of calmidazolium (R 24571) on transmitter release at the frog neuromuscular junction.
The effect of the non-phenothiazine calmodulin-inhibitor R 24571 on transmitter release at the frog neuromuscular junction has been investigated. MEPP frequency was reduced by 25-40% at low concentrations of the drug (2-5 X 10(-7) M) but increased at higher concentrations. These effects were independent of [Ca2+]o. EPP quantal content was increased at low levels of release (quantal content 0.5-1.5) and was unaffected at higher levels (quantal content 30-40). It is concluded that R 24571 has both inhibitory and stimulatory effects, but that evoked release of transmitter is insensitive to the inhibitory action of the drug.
D000818:Animals; D002118:Calcium / Q000502:physiology; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects*; D011896:Rana temporaria; D009435:Synaptic Transmission / Q000187:drug effects*
D007093:Imidazoles; C031938:calmidazolium; D002118:Calcium