IP3-activated Ca2+ channels in the plasma membrane of cultured vascular endothelial cells.
Although it is clear that D-myo-inositol 1,4,5-trisphosphate (IP3) plays an important role in the activation of Ca2+ influx, the mechanisms by which this occurs remain controversial. In an attempt to determine the role of IP3 in the activation of Ca2+ influx, patch-clamp single-channel experiments in the cell-attached, inside-out, and outside-out configurations were performed on cultured bovine aortic endothelial cells (BAEC). The results presented indicate that both IP3 and intracellular Ca2+ can modulate the activity of a Ca(2+)-selective channel found in the plasma membrane of these cells. Addition of 10 microM IP3 increased channel open probability (P(o)) from a control value of 0.12 +/- 0.05 to 0.7 +/- 0.13 at a constant intracellular Ca2+ of 1 nM in excised inside-out patches. D-Myo-inositol 1,3,4,5-tetrakisphosphate at 50 microM was ineffective in altering channel P(o). Channel activity declined after approximately 2 min in the continuous presence of IP3. Three to four minutes after addition of IP3, channel P(o) was reduced from 0.7 +/- 0.2 to 0.2 +/- 0.1, indicating that an additional regulator might be required to maintain channel activity in excised patches. The channel was reversibly blocked by application of 1 microgram/ml heparin to the intracellular side of inside-out patches. This Ca(2+)-selective channel is indistinguishable from the depletion-activated Ca2+ channel we have previously described in BAEC.
Vaca
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Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA.
Kunze
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D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006873:Hydroquinones / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D006873:Hydroquinones; C019359:2,5-di-tert-butylhydroquinone; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D001920:Bradykinin; D002118:Calcium