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Journal of Experimental Biology 153,129-140 (1990)
Published by Company of Biologists 1990

The Neuromuscular Junction Revisited: Ca²⁺ Channels and Transmitter Release in Cholinergic Neurones in Xenopus Nerve and Muscle Cell Culture

T. P. FENG ¹ and ZHENG-SHAN DAI ¹

¹ Shanghai Institute of Physiology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China

Although the entry of calcium ions into the presynaptic nerve terminals through voltage-gated Ca²⁺ channels is now universally recognized as playing an essential role in evoked transmitter release at the neuromuscular junction (NMJ), and indeed in chemical synapses generally, we have as yet very little direct knowledge of the Ca²⁺ channels of the presynaptic terminals. In this work, making use of cocultured nerve and muscle cells from Xenopus embryos, we studied the NMJ formed between the soma of identified cholinergic neurones and myoball, which allowed the use of patch-clamps on both the pre- and postsynaptic components. Both whole-cell and single-channel recordings of Ca²⁺ channels in the presynaptic cell were made. We found only one type of voltage-gated Ca²⁺ channel with highvoltage activation and slow inactivation characteristics, allowing its classification either as the L or the N type. The channels were susceptible to block by metenkephalin but not to block by nifedipine or to enhancement by Bay K 8644. This combination of pharmacological properties favours their classification as the N type. Preliminary observations on the correlation between calcium currents and transmitter release disclosed a strikingly rapid run-down of the evoked release with unchanged calcium currents and spontaneous release during whole-cell recording, indicating a specific wash-out effect on some link between calcium entry and evoked transmitter release.

Key words: neuromuscular junction, calcium channels, transimitter release, Xenopus nerve-muscle culture

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