Evidences for calcium-dependent inactivation of calcium current at the frog motor nerve terminal.
Assessment of calcium-dependent inactivation of calcium current in nerve terminals is not feasible due to technical reasons. Perineural measurement of calcium-flow, however, might be utilized as indirect means to evaluate synaptic currents. Using perineural recording from frog neuromuscular junction, supra-threshold stimuli applied to motor nerve in paired-pulse manner with varying inter-pulse intervals (5-50 ms) are demonstrated in this study to cause paired-pulse depression (PPD) of Ca(2+)-current. PPD of Ca(2+)-flow was reduced at lower extracellular Ca(2+) concentrations, in BAPTA-AM and EGTA-AM treated preparations and after replacing extracellular Ca(2+) with Sr(2+). Using perineural measurement of calcium current as an indirect model to investigate synaptic ionic activity, our findings demonstrate that PPD may be attributed to calcium-dependent inactivation of Ca(2+)-current, which may serve as negative feedback in response to massive Ca(2+) entry to motor nerve terminals. A putative sensor of Ca(2+)-current is also proposed in this study.
Mukhamedyarov
Marat A
MA
Department of Physiology, Kazan State Medical University, ul. Butlerov 49, R-420012 Kazan, Russia.
Grishin
Sergey N
SN
Zefirov
Andrey L
AL
Palotás
András
A
D000818:Animals; D001001:Anura; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009469:Neuromuscular Junction / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D017729:Presynaptic Terminals / Q000502:physiology*
D015220:Calcium Channels; D002614:Chelating Agents; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; C046770:EGTA acetoxymethyl ester; D002118:Calcium