Functional consequences of mutations in the human alpha(1A) calcium channel subunit linked to familial hemiplegic migraine

Mutations in alpha(1A), the pore-forming subunit of P/Q-type calcium channe ls, are linked to several human diseases, including familial hemiplegic mig raine (FHM). We introduced the four missense mutations linked to FHM into h uman alpha(1A-2) subunits and investigated their functional consequences af ter expression in human embryonic kidney 293 cells. By combining single-cha nnel and whole-cell patch-clamp recordings, we show that all four mutations affect both the biophysical properties and the density of functional chann els. Mutation R192Q in the S4 segment of domain I increased the density of functional P/Q-type channels and their open probability. Mutation T666M in the pore loop of domain II decreased both the density of functional channel s and their unitary conductance (from 20 to 11 pS). Mutations V714A and [18 15L in the S6 segments of domains II and IV shifted the voltage range of ac tivation toward more negative voltages, increased both the open probability and the rate of recovery from inactivation, and decreased the density of f unctional channels. Mutation V714A decreased the single-channel conductance to 16 pS. Strikingly, the reduction in single-channel conductance induced by mutations T666M and V714A was not observed in some patches or periods of activity, suggesting that the abnormal channel may switch on and off, perh aps depending on some unknown factor. Our data show that the FHM mutations can lead to both gain- and loss-of-function of human P/Q-type calcium chann els.