Direct measurement of the concentration- and time-dependent open probability of the nicotinic acetylcholine receptor channel.
Using the outside-out patch clamp recording technique together with a rapid solution exchange system, we measured ionic currents through nicotinic acetylcholine (ACh) receptor channels from BC3H-1 cells in response to rapid applications of 0.3-1,000 microM ACh. We used nonstationary fluctuation analysis of ensembles of responses to deduce the number of channels in the patch, the maximum open channel probability as a function of ACh concentration and the time course of a fast desensitization process. We found that: (a) Excised patches from BC3H-1 cells typically contain between 50 and 150 functional ACh receptor ion channels. (b) The open channel probability is proportional to [ACh]1.95 at low concentrations of ACh, is half-maximal at 20 microM ACh and saturates above 100 microM ACh. (c) ACh is a very efficacious agonist; 100 microM ACh opens at least 90% of the available channels. This estimate of efficacy is model-independent. (d) The rate of decay of the agonist-induced current is concentration-dependent. In the presence of 100 microM ACh the current decays with a time constant of 50-100 ms. It decays more slowly in the presence of lower concentrations of agonist but is relatively insensitive to voltage.
Dilger
J P
JP
Department of Anesthesiology, State University of New York, Stony Brook 11794-8480.
Brett
R S
RS
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D051379:Mice; D008809:Mice, Inbred C3H; D008954:Models, Biological; D011336:Probability; D011978:Receptors, Nicotinic / Q000502:physiology*; D013997:Time Factors
D007473:Ion Channels; D011978:Receptors, Nicotinic