1. Coexpression of the β subunit with the α1C subunit of the cardiac L-type Ca2+ channel has been shown to increase ionic current. To examine the mechanism of this increase, ionic and gating currents were measured in transiently transfected HEK293 cells. 2. β1A subunit coexpression increased the maximal whole-cell conductance (Gmax) measured in 10 mM Ba2+ from 91 ± 11 to 833 ± 107 pS pF-1 without a change in the voltage dependence of activation (V1/2: -6·1 ± 1·1 and -6·6 ± 0·9 mV, respectively). 3. Gating currents were smaller in cells expressing only the α1C subunit (only four out of eleven cells exhibited gating currents above the limits of detection, whereas eight out of eight β1A coexpressing cells had measurable gating currents). The gating currents were integrated to measure the intramembrane charge movement (Q). The ON charge movement (Qon) could be described by a Boltzmann distribution reaching a maximal value of Qon,max. 4. The mean ratio of Gmax : Qon,max increased from 99 ± 6 to 243 ± 30 pS fC-1 with β1A coexpression, demonstrating that the β1A subunit changes the gating of α1C channels to favour the opening of the channels. However, this 2·5-fold change in the Gmax : Qon,max ratio explains less than half of the 9·2-fold increase in Gmax with β1A subunit coexpression. The major effect is due to a 3·7-fold increase in Qon,max, demonstrating that β1A subunit coexpression increases the number of functional surface membrane channels.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Physiology|
|State||Published - Apr 1 1996|
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