Ca2+ influx through voltage-gated Ca2+ channels regulates 5-HT3 receptor channel desensitization in rat glioma x mouse neuroblastoma hybrid NG108-15 cells.
1. The kinetics of desensitization of the 5-HT3 receptor (5-HT3R)-gated ion channel were investigated using whole-cell and perforated-patch recording techniques in NG108-15 cells. 2. Rapid application of 5-HT (50 microM) elicited a 5-HT3R-mediated inward current response that desensitized completely in the continued presence of agonist. In the whole-cell recording configuration (holding potential of -70 mV) while buffering internal calcium (Cai2+) with 5 mM EGTA (0.5 mM added Ca2+; with an estimated free [Ca2+] of 30 nM), the rate of desensitization was initially rapid (with a half-time of approximately 230 ms), but dramatically slowed with time by 1120 +/- 160%. 3. This slowing in the rate of desensitization was reduced by stronger Ca2+ buffering (20 mM BAPTA, without added Ca2+), or by the bath application of cadmium (100 microM) to block voltage-gated Ca2+ channels. The rate of desensitization was also dependent on membrane potential. 4. In perforated-patch recordings, the rate of desensitization remained constant. However, a slowing in the desensitization rate could be induced by depolarizing cells immediately prior to the application of 5-HT. 5. The depolarization-induced slowing was blocked by incubating cells with BAPTA-AM (a membrane-permeant analogue of BAPTA) or by the bath application of cadmium. 6. These data suggest that Ca2+ influx through a cadmium-sensitive voltage-gated Ca2+ channel increases the cytoplasmic Ca2+ concentration ([Ca2+]i) and induces a dramatic slowing in the kinetics of desensitization of the 5-HT3R channel. These data provide evidence for cross-talk between voltage-gated Ca2+ channels and 5-HT3Rs in NG108-15 cells.
Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
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D000818:Animals; D001932:Brain Neoplasms / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism* / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D005910:Glioma / Q000378:metabolism; D006822:Hybrid Cells; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D011985:Receptors, Serotonin / Q000502:physiology*
D015220:Calcium Channels; D002614:Chelating Agents; D011985:Receptors, Serotonin; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium