P-type Ca2+ channels mediate excitatory and inhibitory synaptic transmitter release in crayfish muscle

Alfonso Araque, François Clarac, Washington Buño

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51 Scopus citations


The toxin fraction (FTX) and peptide ω-Aga-IVA from the venom of the funnel-web spider Agelenopsis aperta, as well as a synthetic analogue of FTX, specifically block the P-type voltage-dependent Ca2+ channel (VDCC). The effects of these toxins on synaptic transmission were studied in the neuromuscular synapses of the crayfish opener muscle, which has a single excitatory and a single inhibitory motoneuron. FTX selectively and reversibly blocked excitatory and inhibitory postsynaptic currents and potentials in a dose-dependent manner. FTX had no effect on (i) resting and postsynaptic membrane conductance, (ii) postsynaptic L-type VDCC, and (iii) both glutamate- and γ-aminobutyric acid-induced postsynaptic responses. Mean amplitude and frequency of miniature postsynaptic potentials were unchanged by FTX. The postsynaptic VDCC was inhibited by nifedipine, a selective dihydropyridine antagonist of L-type VDCC, whereas synaptic transmission was unaffected. Transmission was also undisturbed by ω-conotoxin, suggesting that N-type VDCCs are not involved. The peptide ω-Aga-IVA blocked excitatory and inhibitory transmission without affecting postsynaptic VDCC. Synaptic transmission was also blocked by synthetic FTX. We conclude that presynaptic P-type VDCCs are involved in both evoked excitatory and inhibitory transmitter release in crayfish neuromuscular synapses.

Original languageEnglish (US)
Pages (from-to)4224-4228
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number10
StatePublished - May 10 1994


  • Polyamines
  • Presynaptic block
  • Synaptic transmission


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