Activation of recombinant trp by thapsigargin in Sf9 insect cells.
The mammalian protein responsible for Ca2+ release-activated current (Icrac) may be homologous to the Drosophila protein designated trp. Thus the activity of trp, and another Drosophila protein designated trp-like or trpl, may be linked to depletion of the internal Ca2+ store via the so-called capacitative Ca2+ entry mechanism. To test this hypothesis, the effect of thapsigargin, a selective inhibitor of the endoplasmic reticulum Ca2+ pump, on trp- and trpl-induced whole cell membrane current was determined using the baculovirus Sf9 insect cell expression system. The results demonstrate that trp and trpl form Ca(2+)-permeable cation channels. The trpl encodes a nonselective cation channel that is constitutively active under basal nonstimulated conditions and is unaffected by thapsigargin, whereas trp is more selective for Ca2+ than Na+ and is activated by depletion of the internal Ca2+ store. Although evaluation of cation selectivity suggests that trp is not identical to the channel responsible for Icrac, these channels must share some structural feature(s) since both are activated by thapsigargin. A unique proline-rich region in the COOH-terminal tail of trp, which is absent in trpl, may be necessary for capacitative Ca2+ entry.
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030.
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Vaca
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Sinkins
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Hu
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Kunze
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Schilling
D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002460:Cell Line; D018076:DNA, Complementary; D004330:Drosophila; D029721:Drosophila Proteins; D004594:Electrophysiology; D005822:Genetic Vectors; D007301:Insect Hormones / Q000235:genetics / Q000378:metabolism*; D019476:Insect Proteins; D007313:Insecta / Q000166:cytology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018002:Receptors, Bradykinin / Q000235:genetics; D011994:Recombinant Proteins; D011995:Recombination, Genetic; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin; D050051:Transient Receptor Potential Channels; D014777:Virus Diseases / Q000503:physiopathology
D015220:Calcium Channels; D018076:DNA, Complementary; D029721:Drosophila Proteins; D007301:Insect Hormones; D019476:Insect Proteins; D008565:Membrane Proteins; D018002:Receptors, Bradykinin; D011994:Recombinant Proteins; D013729:Terpenes; D050051:Transient Receptor Potential Channels; C063169:trp protein, Drosophila; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium