Differential Ca2+-dependence of transmitter release mediated by P/Q- and N-type calcium channels at neonatal rat neuromuscular junctions.
N- and P/Q-type voltage dependent calcium channels (VDCCs) mediate transmitter release at neonatal rat neuromuscular junction (NMJ). Thus the neonatal NMJ allows an examination of the coupling of different subtypes of VDCCs to the release process at a single synapse. We studied calcium dependence of transmitter release mediated by each channel by blocking with omega-conotoxin GVIA the N-type channel or with omega-agatoxin IVA the P/Q-type channel while changing the extracellular calcium concentration ([Ca2+]o). Transmitter release mediated by P/Q-type VDCCs showed steeper calcium dependence than N-type mediated release (average slope 3.6 +/- 0.09 vs. 2.6 +/- 0.03, respectively). Loading the nerve terminals with 10 microm BAPTA-AM in the extracellular solution reduced transmitter release and occluded the blocking effect of omega-conotoxin GVIA (blockade -2 +/- 9%) without affecting the action of omega-agatoxin IVA (blockade 85 +/- 4%). Both VDCC blockers were able to reduce the amount of facilitation produced by double-pulse stimulation. In these conditions facilitation was restored by increasing [Ca2+]o. The facilitation index (fi) was also reduced by loading nerve terminals with 10 microm BAPTA-AM (fi = 1.2 +/- 0.1). The control fi was 2.5 +/- 0.1. These results show that P/Q-type VDCCs were more efficiently coupled to neurotransmitter release than were N-type VDCCs at the neonatal neuromuscular junction. This difference could be accounted for by a differential location of these channels at the release site. In addition, our results indicate that space-time overlapping of calcium domains was required for facilitation.
Rosato-Siri
Marcelo D
MD
Laboratorio de Fisiología y Biología Molecular, Departamento de Biología, Facultad de Ciencias, Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pab. II 2 do piso, Buenos Aires (1428), Argentina.
Piriz
Joaquin
J
Tropper
Barbara A Giugovaz
BA
Uchitel
Osvaldo D
OD
D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000378:metabolism*; D020865:Calcium Channels, P-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004558:Electric Stimulation; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism; D018482:Muscle, Skeletal / Q000294:innervation; D009469:Neuromuscular Junction / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D020865:Calcium Channels, P-Type; D002614:Chelating Agents; D018377:Neurotransmitter Agents; D020867:omega-Agatoxin IVA; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D020866:omega-Conotoxin GVIA; D004492:Edetic Acid; D002118:Calcium