EFFECTS OF HIGH-PRESSURE ON THE CHANNEL GATED BY THE QUISQUALATE-SENSITIVE GLUTAMATE-RECEPTOR OF LOCUST MUSCLE AND ITS BLOCKADE BY KETAMINE- A SINGLE-CHANNEL ANALYSIS

The effects of high pressure on the channel gating kinetics of the qui squalate-sensitive L-glutamate receptor (qGluR) of locust muscle have been investigated using a megaohm seal patch-clamp technique. Pressure was applied with helium gas and recordings were carried out at 20.5-d egrees-C with Rb+ as the main charge-carrying cation in the patch pipe tte. The mean open time of the qGluR channel was unaffected by 10 and 30 MPa, but it was significantly reduced at 50 MPa. A high proportion of brief openings (mean 0.808 ms) was seen at 50 MPa but not at lesser pressures. Also, in contrast to lesser pressures, 50 MPa prolonged th e mean closed time and reduced both the frequency and probability of c hannel opening. 10(-6) M ketamine significantly reduced the mean chann el open time, as previously reported. A pressure of 10 MPa which alone had no effect on the qGluR channel, restored the mean open time in th e presence of 10(-6) M ketamine to the value obtained in the absence o f the anaesthetic. This implies the shortening of qGluR channel open t ime by ketamine involves a large +DELTAV and, therefore, probably conf ormational changes in the channel. However 10 MPa did not restore the distribution of open times to normal.