Flash photolysis of caged inositol 1,4,5-trisphosphate activates plasma membrane calcium current in human T cells.
Sustained elevation of intracellular Ca2+ by cell surface receptors is often dependent on influx of Ca2+ across the plasma membrane through routes not involving voltage-gated Ca2+ channels. We demonstrate that intracellular release of inositol 1,4,5-trisphosphate (InsP3), either from stimulation of transfected human muscarinic receptors or from photolytic release of caged InsP3, activates whole cell Ca2+ current in the Jurkat T cell line. Whole cell voltage clamp recordings indicate that the current is carried by a Ca(2+)-selective channel that resembles T-type voltage-gated Ca2+ channels in relative conductance of different cation species. Elevation of internal Ca2+ inactivates the channel, whereas internal perfusion with inositol 1,3,4,5-tetrakisphosphate (InsP4) does not affect it. Photolytic release of caged 1-(alpha-glycerophosphoryl)-inositol 4,5-bisphosphate, an analog of InsP3 which activates InsP3 receptors but is not readily metabolized to InsP4, also activates the current. We conclude that generation of InsP3 is sufficient to activate Ca(2+)-selective channels in the plasma membrane of T cells. InsP3 may have its effect indirectly through depletion of Ca2+ stores, or directly with a plasma membrane-associated InsP3 receptor.
Department of Medicine, Falk Cardiovascular Research Center, Stanford University School of Medicine, California 94305-5246.
T V
TV
McDonald
B A
BA
Premack
P
P
Gardner
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000737:chemistry / Q000378:metabolism*; D015640:Ion Channel Gating; D008564:Membrane Potentials; D010782:Photolysis; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D002118:Calcium