The alpha1B Ca2+ channel amino terminus contributes determinants for β subunit-mediated voltage-dependent inactivation properties

Stephens, GJ, Page, KM, Bogdanov, Y and Dolphin, AC (2000) The alpha1B Ca2+ channel amino terminus contributes determinants for β subunit-mediated voltage-dependent inactivation properties. The Journal of Physiology, 525 (2), 377-390. (doi:10.1111/j.1469-7793.2000.t01-1-00377.x).

Abstract

1
Co-expression of auxiliary β subunits with the α1B Ca2+ channel subunit in COS-7 cells resulted in an increase in current density and a hyperpolarising shift in the mid-point of activation. Amongst the β subunits, β2a in particular, but also β4 and β1b caused a significant retardation of the voltage-dependent inactivation compared to currents with α1B alone, whilst no significant changes in inactivation properties were seen for the β3 subunit in this system.

2
Prevention of β2a palmitoylation, by introducing cysteine to serine mutations (β2a(C3,4S)), greatly reduced the ability of β2a to retard voltage-dependent inactivation.

3
Deletion of the proximal half of the α1B cytoplasmic amino terminus (α1BΔ1-55) differentially affected β subunit-mediated voltage-dependent inactivation properties. These effects were prominent with the β2a subunit and, to a lesser extent, with β1b. For β2a, the major effects of this deletion were a partial reversal of β2a-mediated retardation of inactivation and the introduction of a fast component of inactivation, not seen with full-length α1B. Deletion of the amino terminus had no other major effects on the measured biophysical properties of α1B when co-expressed with β subunits.

4
Transfer of the whole α1B amino terminus into α1C (α1bCCCC) conferred a similar retardation of inactivation on α1C when co-expressed with β2a to that seen in parental α1B.

5
Individual (α1B(Q47A) and α1B(R52A)) and double (α1B(R52,54A)) point mutations within the amino terminus of α1B also opposed the β2a-mediated retardation of α1B inactivation kinetics.

6
These results indicate that the α1B amino terminus contains determinants for β subunit-mediated voltage-dependent inactivation properties. Furthermore, effects were β subunit selective. As deletion of the α1B amino terminus only partially opposed β subunit-mediated changes in inactivation properties, the amino terminus is likely to contribute to a complex site necessary for complete β subunit function.

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Contributors

Author: Y Bogdanov

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