P/Q-type calcium channels activate neighboring calcium-dependent potassium channels in mouse motor nerve terminals.
The identity of the voltage-dependent calcium channels (VDCC), which trigger the Ca2+-gated K+ currents (IK(Ca)) in mammalian motor nerve terminals, was investigated by means of perineurial recordings. The effects of Ca2+ chelators with different binding kinetics on the activation of IK(Ca) were also examined. The calcium channel blockers of the P/Q family, omega-agatoxin IVA (omega-Aga-IVA) and funnel-web spider toxin (FTX), have been shown to exert a strong blocking effect on IK(Ca). In contrast, nitrendipine and omega-conotoxin GVIA (omega-CgTx) did not affect the Ca2+-activated K+ currents. The intracellular action of the fast Ca2+ buffers BAPTA and DM-BAPTA prevented the activation of the IK(Ca), while the slow Ca2+ buffer EGTA was ineffective at blocking it. These data indicate that P/Q-type VDCC mediate the Ca2+ influx which activates IK(Ca). The spatial association between Ca2+ and Ca2+-gated K+ channels is discussed, on the basis of the differential effects of the fast and slow Ca2+ chelators.
Protti
D A
DA
Instituto de Biología Celular y Neurociencias: "Pr. Dr. Eduardo P. de Robertis", Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Buenos Aires (1121), Argentina.
Uchitel
O D
OD
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology; D015640:Ion Channel Gating; D007700:Kinetics; D008297:Male; D051379:Mice; D009046:Motor Neurons / Q000378:metabolism*; D009411:Nerve Endings / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002614:Chelating Agents; D015221:Potassium Channels; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; C046770:EGTA acetoxymethyl ester; D002118:Calcium