The Drosophila tweety family: molecular candidates for large-conductance Ca2+-activated Cl- channels.
Calcium-activated chloride currents (I(Cl(Ca))) can be recorded in almost all cells, but the molecular identity of the channels underlying this Cl- conductance is still incompletely understood. Here, I report that tweety, a gene located in Drosophila flightless, possesses five or six transmembrane segments, and that a human homologue of tweety (hTTYH3) is a novel large-conductance Ca2+-activated Cl- channel, while the related gene, hTTYH1, is a swelling-activated Cl- current. hTTYH3 is expressed in excitable tissues, including the heart, brain and skeletal muscle, whereas hTTYH1 is expressed mainly in the brain. Expression of hTTYH3 in CHO cells generated a unique Cl- current activated by an increase in the intracellular Ca2+ concentration. The hTTYH3-induced Cl- current had a linear current-voltage (I-V) relationship, a large single-channel conductance (260 pS) and the anion permeability sequence I- > Br- > Cl-. Like native Ca2+-activated Cl- channels, the hTTYH3 channel showed complex gating kinetics and voltage-dependent inactivation, and was dependent on micromolar intracellular Ca2+ concentration. Expression in CHO cells of an hTTYH1 splice variant that lacks the C-terminal glutamate-rich domain of hTTYH1 (hTTYH1sv) generated a swelling-activated Cl- current. I conclude that investigation of the tweety family will provide important information about large-conductance Cl- channel molecules.
Suzuki
Makoto
M
Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical School 3311-1, Yakushiji, Minamikawachi, Tochigi, 329-0498, Japan. macsuz@jichi.ac.jp
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D020013:Calcium Signaling; D002460:Cell Line; D018118:Chloride Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D029721:Drosophila Proteins / Q000235:genetics*; D018260:Gelsolin / Q000235:genetics*; D006801:Humans; D015640:Ion Channel Gating; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D020033:Protein Isoforms; D014162:Transfection
D018118:Chloride Channels; D002712:Chlorides; D029721:Drosophila Proteins; D018260:Gelsolin; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D020033:Protein Isoforms; C417913:TTYH1 protein, human; C438967:TTYH2 protein, human; C098178:fliI protein, Drosophila