Ca2+-sensitive inactivation of L-type Ca2+ channels depends on multiple cytoplasmic amino acid sequences of the alpha1C subunit.
Ca2+-dependent inactivation of Ca2+ currents is a physiological phenomenon widely associated with L-type Ca2+ channels. Although the pore-forming alpha1C subunit of the channel is the target for Ca2+ binding, the amino acid sequences involved in the binding and/or in the coordination of Ca2+-dependent inactivation are still unclear. Based on previous experiments, we have prepared truncation mutants of a human alpha1C subunit by systematically deleting an EF-hand motif and sequences in a segment of 80 amino acids in the carboxyl-terminal tail. We found that the rate as well as the Ca2+ dependence of inactivation of currents through these mutated channels were very different. We have identified three amino acid sequences, the presence of which is important for Ca2+-dependent inactivation: (i) a putative Ca2+-binding EF-hand motif, (ii) two hydrophilic residues (asparagine and glutamic acid) 77-78 amino acids downstream of the EF-hand motif, and (iii) a putative IQ calmodulin binding motif. We suggest that Ca2+-dependent inactivation is a cooperative process involving several amino acid sequences in cytoplasmic segments of the alpha1C subunit.
Zühlke
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RD
Department of Pharmacology, University of Bern, Friedb¿hlstrasse 49, CH-3010 Bern, Switzerland.
Reuter
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D000595:Amino Acid Sequence; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D016764:Cell Polarity; D003593:Cytoplasm; D004252:DNA Mutational Analysis; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D006801:Humans; D015640:Ion Channel Gating; D008969:Molecular Sequence Data; D009865:Oocytes; D011199:Potentiometry; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D014981:Xenopus
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D001464:Barium; D002118:Calcium