The beta subunit increases Ca2+ currents and gating charge movements of human cardiac L-type Ca2+ channels.
The properties of the gating currents (nonlinear charge movements) of human cardiac L-type Ca2- channels and their relationship to the activation of the Ca2+ channel (ionic) currents were studied using a mammalian expression system. Cloned human cardiac alpha1 + rabbit alpha 2 subunits or human cardiac alpha 1 + rabbit alpha 2 + human beta 3 subunits were transiently expressed in HEK293 cells. The maximum Ca2+ current density increased from -3.9 +/- 0.9 pA/pF for the alpha 1 + alpha 2 subunits to -11.6 +/- 2.2 pA/pF for alpha 1 + alpha 2 + beta 3 subunits. Calcium channel gating currents were recorded after the addition of 5 mM Co2+, using a -P/5 protocol. The maximum nonlinear charge movement (Qmax) increased from 2.5 +/- 0.3 nC/muF for alpha 1 + alpha 2 subunit to 12.1 +/- 0.3 nC/muF for alpha 1 + alpha 2 + beta 3 subunit expression. The QON was equal to the QOFF for both subunit combinations. The QON-Vm data were fit by a sum of two Boltzmann expressions and ranged over more negative potentials, as compared with the voltage dependence for activation of the Ca2+ conductance. We conclude that 1) the beta subunit increases the number of functional alpha 1 subunits expressed in the plasma membrane of these cells and 2) the voltage-dependent activation of the human cardiac L-type calcium channel involves the movements of at least two nonidentical and functionally distinct gating structures.
Josephson
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Department of Molecular and Cellular Physiology, University of Cincinnati, College of Medicine, Ohio 45267-0576, USA. josephson@uc.edu
Varadi
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D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D017136:Ion Transport; D008564:Membrane Potentials; D009206:Myocardium / Q000378:metabolism; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D015220:Calcium Channels; D011994:Recombinant Proteins; D002118:Calcium