CA2-GATED CA2+ CHANNELS REGULATES 5-HT3, RECEPTOR-CHANNEL DESENSITIZATION IN RAT GLIOMA X MOUSE NEUROBLASTOMA HYBRID NG108-15 CELLS( INFLUXTHROUGH VOLTAGE)

1. The kinetics of desensitization of the 5-HT3 receptor (5-HT3R)-gate d ion channel were investigated using whole-cell and perforated-patch recording techniques in NG108-15 cells. 2. Rapid application of 5-HT ( 50 mu M) elicited a 5-HT3R-mediated inward current response that desen sitized completely in the continued presence of agonist. In the whole- cell recording configuration (holding potential of -70 mV) while buffe ring internal calcium (Ca-i(2+)) with 5 mM EGTA (0.5 mM added Ca2+; wi th an estimated free [Ca2+] of 30 nM), the rate of desensitization was initially rapid (with a half-time of similar to 230 ms), but dramatic ally 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 mu M) to block voltage-gated Ca2+ channels. The rate of desensitization was also dependent on membrane potential. 4. In perforated-patch recording s, the rate of desensitization remained constant. However, a slowing i n the desensitization rate could be induced by depolarizing cells imme diately prior to the application of 5-HT. 5. The depolarization-induce d slowing was blocked by incubating cells with BAPTA-AM (a membrane-pe rmeant analogue of BAPTA) or by the bath application of cadmium. 6. Th ese 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 desensitizatio n of the 5-HT3R channel. These data provide evidence for cross-talk be tween voltage-gated Ca2+ channels and 5-HT(3)Rs in NG108-15 cells.