Rapid kinetics of single glutamate-receptor channels

Abstract

Drug-induced ionic channels are known to operate by opening briefly when agonist molecules bind to receptor sites^1–7 to produce rectangular current pulses, the amplitude and lifetime of which can be derived from noise analysis^1–3, or directly recorded using the patch-clamp technique^4–7. If desensitization is neglected, the distributions of channel open and closed times can generally be fitted by single exponential functions^5–7, suggesting that a simple two-stage reaction scheme is sufficient to account for the observed kinetics¹. Using patch-clamp recording with an improved time resolution, we have now found that glutamate-activated channels in locust muscle membrane show a large excess of both brief openings and closings over those expected from single exponential distributions. Many events which, with poorer frequency resolution, would have appeared as single openings were found to consist of two or more openings, interspersed with brief (<300 µs) closings. These observations have interesting implications for receptor/channel functioning.