HUMAN AUTOANTIBODIES SPECIFIC FOR THE ALPHA(1A) CALCIUM-CHANNEL SUBUNIT REDUCE BOTH P-TYPE AND Q-TYPE CALCIUM CURRENTS IN CEREBELLAR NEURONS

The pharmacological properties of voltage-dependent calcium channel (V DCC) subtypes appear mainly to be determined by the alpha(1) pore-form ing subunit but, whether P-and Q-type VDCCs are encoded by the same al pha(1) gene presently is unresolved. To investigate this, we used IgG antibodies to presynaptic VDCCs at motor nerve terminals that underlie muscle weakness in the autoimmune Lambert-Eaton myasthenic syndrome ( LEMS), We first studied their action on changes in intracellular free Ca2+ concentration [Ca2+](i) in human embryonic kidney (HEK293) cell l ines expressing different combinations of human recombinant VDCC subun its. Incubation for 18 h with LEMS IgG (2 mg/ml) caused a significant dose dependent reduction in the K+-stimulated [Ca2+](i) increase in th e alpha(1A) cell line but not in the alpha(1B), alpha(1C), alpha(1D) a nd alpha(1E) cell lines, establishing the alpha(1A) subunit as the tar get for these autoantibodies, Exploiting this specificity, we incubate d cultured rat cerebellar neurones with LEMS IgG and observed a reduct ion in P-type current in Purkinje cells and both P- and Q-type current s in granule cells. These data are consistent with the hypothesis that the alpha(1A) gene encodes for the pore-forming subunit of both P-typ e and Q-type VDCCs.