CALCIUM CURRENTS AND TRANSIENTS OF NATIVE AND HETEROLOGOUSLY EXPRESSED MUTANT SKELETAL-MUSCLE DHP RECEPTOR ALPHA-1 SUBUNITS (R528H)

Rabbit cDNA of the alpha 1 subunit of the skeletal muscle dihydropyrid ine (DHP) receptor was functionally expressed in a muscular dysgenesis mouse (mdg) cell line, GLT. L-type calcium currents and transients we re recorded for the mild type and a mutant alpha 1 subunit carrying an R528H substitution in the supposed voltage sensor of the second chann el domain that is linked to a human disease, hypokalemic periodic para lysis. L-type channels expressed in GLT myotubes exhibited currents si milar to those described for primary cultured mdg cells injected with rabbit wild type cDNA, indicating this system to be useful for functio nal studies of heterologous DHP receptors. Voltage dependence and kine tics of activation and inactivation of L-type calcium currents from mu tant and wild type channels did not differ significantly. Intracellula r calcium release activation measured by fura-2 microfluorimetry was n ot grossly altered by the mutation either. Analogous measurements on m yotubes of three human R528H carriers revealed calcium transients comp arable to controls while the voltage dependence of both activation and inactivation of the L-type current showed a shift to more negative po tentials of approximately 6 mV. Similar effects on the voltage depende nce of the fast T-type current and changes in the expression level of the third-type calcium current point to factors not primarily associat ed with the mutation perhaps participating in disease pathogenesis. (C ) 1998 Federation of European Biochemical Societies.