Biophys J, September 2001, p. 1439-1451, Vol. 81, No. 3

Evidence for Two Concentration-Dependent Processes for -Subunit Effects on 1B Calcium Channels

Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom

-Subunits of voltage-dependent Ca²⁺ channels regulate both their expression and biophysical properties. We have injected a range of concentrations of 3-cDNA into Xenopus oocytes, with a fixed concentration of 1B (Ca_V2.2) cDNA, and have quantified the corresponding linear increase of 3 protein. The concentration dependence of a number of 3-dependent processes has been studied. First, the dependence of the a1B maximum conductance on 3-protein occurs with a midpoint around the endogenous concentration of 3 (~17 nM). This may represent the interaction of the -subunit, responsible for trafficking, with the I-II linker of the nascent channel. Second, the effect of 3-subunits on the voltage dependence of steady-state inactivation provides evidence for two channel populations, interpreted as representing 1B without or with a 3-subunit, bound with a lower affinity of 120 nM. Third, the effect of 3 on the facilitation rate of G-protein-modulated 1B currents during a depolarizing prepulse to +100 mV provides evidence for the same two populations, with the rapid facilitation rate being attributed to G dissociation from the -subunit-bound 1B channels. The data are discussed in terms of two hypotheses, either binding of two -subunits to the 1B channel or a state-dependent alteration in affinity of the channel for the -subunit.

Biophys J, September 2001, p. 1439-1451, Vol. 81, No. 3
© 2001 by the Biophysical Society   0006-3495/01/09/1439/13  $2.00

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