Syntaxin I modulation of presynaptic calcium channel inactivation revealed by botulinum toxin C1.
The chick ciliary ganglion calyx-type nerve terminal was used to examine voltage-sensitive inactivation of presynaptic N-type Ca2+ channels and to test if this inactivation is modulated by the transmitter release-associated protein syntaxin I. We tested the role of this protein with botulinum toxin C1 (BtC1) which cleaves syntaxin I close to its membrane anchor. The presynaptic Ca2+ current inactivated as two distinct populations with approximately 75% inactivating at a depolarized potential, V1/2 approximately -15 mV, with the remainder inactivating at approximately -75 mV. BtC1 had no detectable effect on the latter component but resulted in a approximately 7 mV positive shift in the V1/2 of the -15 mV inactivating component. These results confirm that the bulk of presynaptic N-type Ca2+ channels are in general resistant to voltage dependent inactivation and provide the first direct evidence that the physiological properties of presynaptic nerve terminal Ca2+ channels are subject to modulation by release site-associated proteins.
Stanley
Elise F
EF
Cellular and Molecular Biology Division, MP14-320, Toronto Western Research Institute, University Health Network, 399 Bathurst Street, Toronto ON, Canada.
D000818:Animals; D000954:Antigens, Surface / Q000502:physiology*; D001905:Botulinum Toxins / Q000494:pharmacology*; D020864:Calcium Channels, N-Type / Q000187:drug effects* / Q000502:physiology*; D002642:Chick Embryo; D005724:Ganglia / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials; D009419:Nerve Tissue Proteins / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology*; D050827:Syntaxin 1
D000954:Antigens, Surface; D020864:Calcium Channels, N-Type; D009419:Nerve Tissue Proteins; D050827:Syntaxin 1; D001905:Botulinum Toxins