Electrophysiological properties of the hypokalaemic periodic paralysis mutation (R528H) of the skeletal muscle alpha 1s subunit as expressed in mouse L cells.

Hypokalaemic periodic paralysis (HypoPP) is an autosomal dominant muscle disease which has been linked to point mutations in the skeletal muscle L-type calcium channel alpha 1 subunit (alpha 1s). Here, we have introduced one of the point mutations causing HypoPP (R528H) into cDNA of the rabbit alpha 1s. Expression of either the wild-type alpha 1s or the mutant R528H alpha 1s (alpha 1s-R528H) subunits was obtained in mouse Ltk- cells using a selectable expression vector. The alpha 1s-R528H subunit led to the expression of functional L-type Ca2+ channels. Corresponding whole-cell Ba2+ currents exhibit very slow activation and inactivation kinetics, typical for recombinant skeletal Ca2+ channel currents. Voltage-dependent activation and inactivation properties were similar for alpha 1s- and alpha 1s-R528H, as well as their sensitivity to the dihydropyridine agonist Bay K 8644. Differences in alpha 1s- and alpha 1s-R528H-directed channels reside in the Ba2+ current density, which was significantly reduced 3.2 fold in cells expressing alpha 1s-R528H. It was concluded that the R528H mutation af alpha 1s results in minor differences in the electrophysiological properties but significantly reduces the whole-cell Ca2+ channel current in its amplitude.