Multiple structural domains contribute to voltage-dependent inactivation of rat brain alpha(1E) calcium channels.
We have investigated the molecular determinants that mediate the differences in voltage-dependent inactivation properties between rapidly inactivating (R-type) alpha(1E) and noninactivating (L-type) alpha(1C) calcium channels. When coexpressed in human embryonic kidney cells with ancillary beta(1b) and alpha(2)-delta subunits, the wild type channels exhibit dramatically different inactivation properties; the half-inactivation potential of alpha(1E) is 45 mV more negative than that observed with alpha(1C), and during a 150-ms test depolarization, alpha(1E) undergoes 65% inactivation compared with only about 15% for alpha(1C). To define the structural determinants that govern these intrinsic differences, we have created a series of chimeric calcium channel alpha(1) subunits that combine the major structural domains of the two wild type channels, and we investigated their voltage-dependent inactivation properties. Each of the four transmembrane domains significantly affected the half-inactivation potential, with domains II and III being most critical. In particular, substitution of alpha(1C) sequence in domains II or III with that of alpha(1E) resulted in 25-mV negative shifts in half-inactivation potential. Similarly, the differences in inactivation rate were predominantly governed by transmembrane domains II and III and to some extent by domain IV. Thus, voltage-dependent inactivation of alpha(1E) channels is a complex process that involves multiple structural domains and possibly a global conformational change in the channel protein.
Spaetgens
R L
RL
Department of Pharmacology and Therapeutics, Neuroscience Research Group, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
Zamponi
G W
GW
D000818:Animals; D001921:Brain / Q000502:physiology; D001923:Brain Chemistry; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D020908:Calcium Channels, R-Type; D020747:Calcium Channels, T-Type; D027682:Cation Transport Proteins; D006801:Humans; D015640:Ion Channel Gating; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000502:physiology
C498917:Cacna1e protein, rat; D015220:Calcium Channels; D020908:Calcium Channels, R-Type; D020747:Calcium Channels, T-Type; D027682:Cation Transport Proteins; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins