Single channel kinetics of a glutamate receptor

Abstract

The glutamate receptor-channel of locust muscle membrane was studied using the patch-clamp technique. Muscles were pretreated with concanavalin A to block receptor-channel desensitization, thus facilitating analysis of receptor-channel gating kinetics. Single channel kinetics were analyzed to aid in identification of the molecular basis of channel gating. Channel dwell-time distributions and dwell-time autocorrelation functions were calculated from single channel data recorded in the precence of 10-4M glutamate. Analysis of the dwell time distributions in terms of mixtures of exponential functions revealed there to be at least three open states of the receptor-channel and at least four closed states. Autocorrelation function analysis showed there to be at least three pathways linking the open states with the closed. This results in a minimal scheme for gating of the glutamate receptor-channel, which is suggestive of allosteric models of receptor-channel gating.

Markov, fractal, diffusion, and related models of ion channel gating. A comparison with experimental data from two ion channels

“…Glutamate receptor channels were recorded using the megaohm patch clamp, as described by Kerry et al (1987). A two-electrode voltage clamp was used to maintain the membrane potential at -110 mV, and the muscle was pretreated with concanavalin A to block desensitization.…”

“…Single-channel recordings were filtered at 3 kHz on playback, and analyzed using the dual-threshold crossing method as described by Kerry et al (1987). The open and closed (dwell) times were written to disc.…”

“…Given that our understanding of protein dynamics is incomplete, we feel that the only way to discriminate between alternative gating models is by careful statistical analysis of single channel data. To this end we have analyzed the gating kinetics of the two channels, the locust muscle qGluR (Kerry et al, 1987(Kerry et al, , 1988) and a delayed rectifier-type K+ channel from NG108-15 cells (McGee et al, 1988), in terms of six different classes of gating models. A preliminary account of this work has appeared in abstract form .…”

Single-channel autocorrelation functions: the effects of time interval omission

“…We will examine in some detail the situation where a = 10-4 M and rO = 0.2 ms. This corresponds to the experimental work of Kerry et al (1987a). We label 1, 2, 3, 4, 5 the open states 0, OA, OA2, OA3, OA4, and 6, 7, 8, 9, 10 the closed states C, CA, CA2, CA3, CA4.…”

“…The above form of time interval omission is assumed for ease of exposition, although it should be noted that it corresponds to the imposition of a consistent minimum sojourn time, as suggested by e.g., Colquhoun and Sigworth (1983). The following may be readily modified to incorporate (a) different values of r0 for open and closed sojourns, and (b) a specified distribution for r0, as in Kerry et al (1987a). The mathematical details for the more general case may be found in Ball and Sansom (1988), where formal proofs are provided.…”