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 quisqualate-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 degrees C with Rb+ as the main charge-carrying cation in the patch pipette. 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 the mean closed time and reduced both the frequency and probability of channel opening. 10(-6) M ketamine significantly reduced the mean channel 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 the presence of 10(-6) M ketamine to the value obtained in the absence of the anaesthetic. This implies the shortening of qGluR channel open time by ketamine involves a large + delta V and, therefore, probably conformational changes in the channel. However 10 MPa did not restore the distribution of open times to normal.