Relation between intracellular Ca2+ signals and Ca(2+)-activated Cl- current in Xenopus oocytes.
Activation of inositol 1,4,5-trisphosphate (InsP3) signalling in Xenopus oocytes causes intracellular Ca2+ mobilization and thereby activates a Ca(2+)-dependent Cl- membrane conductance. Measurements of cytosolic Ca2+ levels using fluorescent indicators, however, revealed little correspondence with Cl- currents. Intracellular photorelease of InsP3 from a caged precursor evoked transient currents that peaked while the Ca(2+)-fluorescence signal was rising, and subsequently declined within a few seconds, even though the Ca2+ signal remained elevated much longer. Also, Cl- currents evoked by agonist activation showed transient spikes while a wave of Ca2+ liberation swept across the cell, but then decreased when the Ca2+ signal attained a maximal level. Thus, the Cl- current corresponded better to the rate of rise of intracellular free Ca2+, rather than to its steady state level. Experiments using paired flashes to photolyse caged InsP3 and caged Ca2+ indicated that this relationship did not arise through desensitization or inactivation of the Cl- conductance. Furthermore, fluorescence measurements made at different depths into the cell using a confocal microscope revealed no evidence that a rapid decline of local Ca2+ levels near the plasma membrane was responsible for the decay of Ca(2+)-activated Cl- current. Instead, Cl- channels may show an adaptive or incremental response to Ca2+, which is likely to be important for the encoding and transmission of information by Ca2+ spikes.
Parker
I
I
Department of Psychobiology, University of California at Irvine.
Yao
Y
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004396:Coloring Agents; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism*; D015398:Signal Transduction; D014981:Xenopus
D002712:Chlorides; D004396:Coloring Agents; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium