title: Voltage-dependent facilitation of cardiac L-type Ca channels expressed in HEK-293 cells requires beta-subunit.
abstract: The activity of native L-type Ca channels can be facilitated by strong depolarizations. The cardiac Ca channel alpha(1C)-subunit was transiently expressed in human embryonic kidney (HEK-293) cells, but these channels did not exhibit voltage-dependent facilitation. Coexpression of the Ca channel beta(1a)- or beta(2a)-subunit with the alpha(1C)-subunit enabled voltage-dependent facilitation in 40% of cells tested. The onset of facilitation in alpha(1C) + beta(1a)-expressing HEK-293 cells was rapid after a depolarization to +100 mV (tau = 7.0 ms). The kinetic features of the facilitated currents were comparable to those observed for voltage-dependent relief of G protein inhibition demonstrated for many neuronal Ca channels; however, intracellular dialysis with guanosine 5'-O-(2-thiodiphosphate) and guanosine 5'-O-(3-thiotriphosphate) in the patch pipette had no effect on facilitation. Stimulation of G protein-coupled receptors, either endogenous (somatostatin receptors) or coexpressed (adenosine A(1) receptors), did not affect voltage-dependent facilitation. These results indicate that the cardiac Ca channel alpha(1C)-subunit can exhibit voltage-dependent facilitation in HEK-293 cells only when coexpressed with an auxiliary beta-subunit and that this facilitation is independent of G protein pathways.
authors.affiliation: Departments of Medicine and Physiology, University of Wisconsin-Madison, Madison, Wisconsin 53792, USA. tjk@medicine.wisc.edu
authors.forename: T J
authors.initials: TJ
authors.lastname: Kamp
authors.forename: H
authors.initials: H
authors.lastname: Hu
authors.forename: E
authors.initials: E
authors.lastname: Marban
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D001464:Barium / Q000502:physiology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D004553:Electric Conductivity; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D009206:Myocardium / Q000378:metabolism*; D020033:Protein Isoforms / Q000502:physiology*; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D020746:Calcium Channels, L-Type; D020033:Protein Isoforms; D013873:Thionucleotides; D001464:Barium; C030812:adenosine 5'-O-(2-thiodiphosphate); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000244:Adenosine Diphosphate; D019204:GTP-Binding Proteins