title: Evidence for a specific site for modulation of calcium channel activation by external calcium ions.
abstract: We have investigated the effect of permeant ion species on activation of transiently expressed neuronal alpha1A Ca channels. Equimolar replacement of Ba with Ca resulted in a consistent depolarizing shift of the half-activation potential whose magnitude (&sim;10 mV) was constant over a range of 2 to 100 mM permeant ion, suggesting that the effects of Ca ions were fully developed at concentrations below 2 mM and indicating that Ba and Ca screened surface charges equally. In mixtures of Ba and Ca at constant divalent cation concentration the voltage-shift, as a function of Ca mole fraction, was well described by a model in which Ba and Ca compete for a single site but only Ca ions produce a gating effect. Overall, our data are consistent with Ca ions exerting their effects on activation via a specific regulatory site.
authors.affiliation: University of British Columbia, Biotechnology Laboratory, 6174 University Blvd., Vancouver, V6T 1Z3, Canada.
authors.forename: G W
authors.initials: GW
authors.lastname: Zamponi
authors.forename: T P
authors.initials: TP
authors.lastname: Snutch
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D009865:Oocytes / Q000737:chemistry; D013499:Surface Properties; D014982:Xenopus laevis
chemical_list: D015220:Calcium Channels; D001464:Barium; D002118:Calcium