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 (I _K(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 I _K(Ca) were also examined. The calcium channel blockers of the P/Q family, ω-agatoxin IVA (ω-Aga-IVA) and funnel-web spider toxin (FTX), have been shown to exert a strong blocking effect on I _K(Ca). In contrast, nitrendipine and ω-conotoxin GVIA (ω-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 I _K(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 I _K(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. Received: 20 December 1996 / Received after revision: 21 March 1997 / Accepted: 2 April 1997