Three New Familial Hemiplegic Migraine Mutants Affect P/Q-type Ca²⁺ Channel Kinetics*

Missense mutations in the pore-forming human α_1A subunit of neuronal P/Q-type Ca²⁺channels are associated with familial hemiplegic migraine. We studied the functional consequences on P/Q-type Ca²⁺ channel function of three recently identified mutations, R583Q, D715E, and V1457L after introduction into rabbit α_1A and expression in Xenopus laevis oocytes. The potential for half-maximal channel activation of Ba²⁺ inward currents was shifted by > 9 mV to more negative potentials in all three mutants. The potential for half-maximal channel inactivation was shifted by > 7 mV in the same direction in R583Q and D715E. Biexponential current inactivation during 3-s test pulses was significantly faster in D715E and slower in V1457L than in wild type. Mutations R583Q and V1457L delayed the time course of recovery from channel inactivation. The decrease of peak current through R583Q (30.2%) and D715E (30.1%) but not V1457L (18.7%) was more pronounced during 1-Hz trains of 15 100-ms pulses than in wild type (18.2%). Our data demonstrate that the mutations R583Q, D715E, and V1457L, like the previously reported mutations T666M, V714A, and I1819L, affect P/Q-type Ca²⁺channel gating. We therefore propose that altered channel gating represents a common pathophysiological mechanism in familial hemiplegic migraine.