title: Coexpression of cloned alpha(1B), beta(2a), and alpha(2)/delta subunits produces non-inactivating calcium currents similar to those found in bovine chromaffin cells.
abstract: Chromaffin cells express N-type calcium channels identified on the basis of their high sensitivity to block by omega-conotoxin GVIA (omega-CgTx GVIA). In contrast to neuronal N-type calcium currents that inactivate during long depolarizations and that require negative holding potentials to remove inactivation, many chromaffin cells exhibit N-type calcium channel currents that show little inactivation during maintained depolarizations and that exhibit no decrease in channel availability at depolarized holding potentials. N-type calcium channels are thought to be produced by combination of the pore-forming alpha(1B) subunit and accessory beta and alpha(2)/delta subunits. To examine the molecular composition of the non-inactivating N-type calcium channel, we cloned the alpha(1B) and accessory beta (beta(1b), beta(1c,) beta(2a), beta(2b), and beta(3a)) subunits found in bovine chromaffin cells. Expression of the subunits in either Xenopus oocytes or human embryonic kidney 293 cells produced high-threshold calcium currents that were blocked by omega-CgTx GVIA. Coexpression of bovine alpha(1B) with beta(1b), beta(1c), beta(2b), or beta(3a) produced currents that were holding potential dependent. In contrast, coexpression of bovine alpha(1B) with beta(2a) produced holding potential-independent calcium currents that closely mimicked native non-inactivating currents, suggesting that non-inactivating N-type channels consist of bovine alpha(1B), alpha(2)/delta, and beta(2a).
authors.affiliation: The Department of Neurobiology, The University of Chicago, Chicago, Illinois 60637, USA. acahill@Drugs.bsd.uchicago.edu
authors.forename: A L
authors.initials: AL
authors.lastname: Cahill
authors.forename: J H
authors.initials: JH
authors.lastname: Hurley
authors.forename: A P
authors.initials: AP
authors.lastname: Fox
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000737:chemistry* / Q000502:physiology; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004594:Electrophysiology; D005260:Female; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000235:genetics*; D007668:Kidney / Q000166:cytology; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D051381:Rats; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D018076:DNA, Complementary; D020866:omega-Conotoxin GVIA; D002118:Calcium