Reduced voltage sensitivity of activation of P/Q-type Ca²⁺ channels is associated with the ataxic mouse mutation rolling Nagoya (tg(rol))

Recent genetic analyses have revealed an important association of the gene encoding the P/Q-type voltage-dependent Ca²⁺ channel α(1A) subunit with hereditary neurological disorders. We have identified the ataxic mouse mutation, rolling Nagoya (tg(rol)), in the α(1A) gene that leads to a charge-neutralizing arginine-to-glycine substitution at position 1262 in the voltage sensor-forming segment S4 in repeat III. Ca²⁺ channel currents in acutely dissociated Purkinje cells, where P-type is the dominant type, showed a marked decrease in slope and a depolarizing shift by 8 mV of the conductance-voltage curve and reduction in current density in tg(rol) mouse cerebella, compared with those in wild-type. Compatible functional change was induced by the tg(rol) mutation in the recombinant α(1A) channel, indicating that a defect in voltage sensor of P/Q-type Ca²⁺ channels is the direct consequence of the tg(rol) mutation. Furthermore, somatic whole-cell recording of mutant Purkinje cells displayed only abortive Na⁺ burst activity and hardly exhibited Ca²⁺ spike activity in cerebellar slices. Thus, in tg(rol) mice, reduced voltage sensitivity, which may derive from a gating charge defect, and diminished activity of the P-type α(1A) Ca²⁺ channel significantly impair integrative properties of Purkinje neurons, presumably resulting in locomotor deficits.