[A new type of IP3-sensitive highly selective calcium channels of low conductance in the plasma membrane of carcinoma A 431 cells].
Application of 0.2-15.0 mM inositol 1,4,5-trisphosphate (IP3) to excised plasma membrane patches from A 431 cells induced activity of low conductance channels that were highly selective for Ca2+ and Ba2+. With 100 mM Ca2+ or 105 mM Ba2+, the channel conductance was 1.1 pS for the minor conductance substrate. The dose response curve gave an apparent binding constant of 0.18 microM IP3. The channel open probability displayed a strong potential dependence: it decreased markedly upon depolarization, and the half-maximum value was achieved at 73 mV. The dependence of channel activity on the intracellular free Ca2+ concentration was bell shaped, but markedly different from that reported for endoplasmic IP3 receptor. The same channels were detected in intact cells upon application of calcium mobilizing reagents. The activity induced in cell attached mode disappeared after patch excision but could be resumed by application of IP3. The data obtained argue for IP3 acting directly on plasma membrane Ca2+ channels.
Kiselev
K I
KI
Mamin
A G
AG
Semenova
S B
SB
Mozhaeva
G N
GN
D001464:Barium / Q000378:metabolism; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D002294:Carcinoma, Squamous Cell; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D013268:Stimulation, Chemical; D014407:Tumor Cells, Cultured; D014544:Uridine Triphosphate / Q000494:pharmacology
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D001464:Barium; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D001920:Bradykinin; D002118:Calcium; D014544:Uridine Triphosphate