The action of verapamil on the rate of spontaneous release of transmitter at the frog neuromuscular junction.
Verapamil is known to reduce Ca2+ entry in a variety of cells. At 10(-5) M it produces a small reduction in MEPP frequency at the frog neuromuscular junction, whereas the rate of spontaneous release rises following treatment at a concentration of 10(-4) M. This latter effect is augmented by raising [Ca2+]0 to 9 mM or, more especially, by raising the temperature from 17 to 23 degrees C. It is argued that both these opposing effects are related to the action of verapamil in modifying [Ca2+]i at the presynaptic terminals and it is suggested that the drug can affect both inward Ca2+ flux (so reducing the steady-state position of [Ca2+]i) and also, at higher concentration, either inhibit the membrane Ca2+ pump or cause the release of Ca2+ from intracellular Ca2+ stores (so raising [Ca2+]i).
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001001:Anura; D002118:Calcium / Q000378:metabolism; D003620:Dantrolene / Q000494:pharmacology; D005260:Female; D005711:Gallopamil / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009045:Motor Endplate / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D011894:Rana pipiens; D013696:Temperature; D013806:Theophylline / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology*
D018377:Neurotransmitter Agents; D005711:Gallopamil; D013806:Theophylline; D014700:Verapamil; D003620:Dantrolene; D002118:Calcium