Familial Hemiplegic Migraine Type 1 Mutations K1336E, W1684R, and V1696I Alter Cav2.1 Ca2+ Channel Gating: EVIDENCE FOR β-SUBUNIT ISOFORM-SPECIFIC EFFECTS

Carmen Müllner,Ludo A.M Broos,Arn M.J.M Van Den Maagdenberg,Jörg Striessnig

doi:10.1074/jbc.m408756200

Abstract

Mutations in the Cav2.1 alpha1-subunit of P/Q-type Ca2+ channels cause human diseases, including familial hemiplegic migraine type-1 (FHM1). FHM1 mutations alter channel gating and enhanced channel activity at negative potentials appears to be a common pathogenetic mechanism. Different beta-subunit isoforms (primarily beta4 and beta3) participate in the formation of Cav2.1 channel complexes in mammalian brain. Here we investigated not only whether FHM1 mutations K1336E (KE), W1684R (WR), and V1696I (VI) can affect Cav2.1 channel function but focused on the important question whether mutation-induced changes on channel gating depend on the beta-subunit isoform. Mutants were co-expressed in Xenopus oocytes together with beta1, beta3, or beta4 and alpha2delta1 subunits, and channel function was analyzed using the two-electrode voltage-clamp technique. WR shifted the voltage dependence for steady-state inactivation of Ba2+ inward currents (IBa) to more negative voltages with all beta-subunits tested. In contrast, a similar shift was observed for KE only when expressed with beta3. All mutations promoted IBa decay during pulse trains only when expressed with beta1 or beta3 but not with beta4. Enhanced decay could be explained by delayed recovery from inactivation. KE accelerated IBa inactivation only when co-expressed with beta3, and VI slowed inactivation only with beta1 or beta3. KE and WR shifted channel activation of IBa to more negative voltages. As the beta-subunit composition of Cav2.1 channels varies in different brain regions, our data predict that the functional FHM1 phenotype also varies between different neurons or even within different neuronal compartments.

Highlights

Mutations in the Cav2.1 ␣1-subunit of P/Q-type Ca2؉ channels cause human diseases, including familial hemiplegic migraine type-1 (FHM1)
Increased action potential-evoked Ca2ϩ influx and neurotransmitter release can explain the facilitation of cortical spreading depression [15] and phenomena of enhanced cortical network hyperexcitability associated with common forms of migraine [8]. The validity of this gain-of-function hypothesis is challenged by two important questions: (i) As Cav2.1 channels can associate with different ␤-subunits in mammalian brain (mainly ␤3, ␤4, and ␤1 (16 –18)) the functional effects of FHM1 mutations may vary depending on the associated ␤-subunit; (ii) so far only seven of at least sixteen known FHM1 mutations have been analyzed functionally
VI in helix IVS5 is the first FHM1 mutation in a S5 helix subjected to electrophysiological analysis

Summary

Introduction

Mutations in the Cav2.1 ␣1-subunit of P/Q-type Ca2؉ channels cause human diseases, including familial hemiplegic migraine type-1 (FHM1). Increased action potential-evoked Ca2ϩ influx and neurotransmitter release can explain the facilitation of cortical spreading depression [15] and phenomena of enhanced cortical network hyperexcitability associated with common forms of migraine [8] The validity of this gain-of-function hypothesis is challenged by two important questions: (i) As Cav2.1 channels can associate with different ␤-subunits in mammalian brain (mainly ␤3, ␤4, and ␤1 (16 –18)) the functional effects of FHM1 mutations may vary depending on the associated ␤-subunit; (ii) so far only seven of at least sixteen known FHM1 mutations have been analyzed functionally. It remains unclear whether all FHM1 mutants can induce the observed negative shift in activation gating

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Results

Conclusion