Abstract
The involvement of the different types of voltage-dependent calcium channels (VDCC) in both DM-BAPTA-AM-incubated and EGTA-AM-incubated mature mice levator auris neuromuscular junctions (NMJ) was studied. We evaluated the effects of ω-agatoxin IVA (ω-Aga IVA), nitrendipine and ω-conotoxin GVIA (ω-CgTX) (P/Q-, L- and N-type VDCC blockers, respectively) on perineurial calcium currents (I Ca) and nerve-evoked transmitter release. The application of ω-Aga IVA (100 nM) drastically reduced perineurial I Ca (>90%) and nerve-evoked transmitter release (>90% of reduction in quantal content, m) at both DM-BAPTA-AM-incubated and EGTA-AM-incubated NMJ. The L-type VDCC antagonist nitrendipine (10 µM) caused a significant reduction (23±9%, n=5) of perineurial I Ca at DM-BAPTA-AM-incubated NMJ. In addition, after the block of P/Q-type VDCC with ω-Aga IVA (100 nM), nitrendipine reduced (>90%, n=2) the remaining perineurial I Ca. Such reduction was not observed at EGTA-AM-incubated NMJ, before or after the total block of P/Q-type VDCC. Moreover, nitrendipine did not significantly reduce the quantal content of DM-BAPTA-AM-incubated NMJ. Finally, the application of ω-CgTX (5 µM) did not significantly affect perineurial I Ca or nerve-evoked transmitter release at either DM-BAPTA-AM-incubated or EGTA-AM-incubated NMJ. These results show the existence of a nitrendipine-sensitive, L-type component of perineurial I Ca in DM-BAPTA-AM-incubated NMJ of mature mice.
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Received: 2 September 1998 / Received after revision:13 October 1998 / Accepted:14 October 1998
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Urbano, F., Uchitel, O. L-Type calcium channels unmasked by cell-permeant Ca2+ buffer at mouse motor nerve terminals. Pflügers Arch 437, 523–528 (1999). https://doi.org/10.1007/s004240050813
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DOI: https://doi.org/10.1007/s004240050813