title: Kinetic properties of the glycine receptor main- and sub-conductance states of mouse spinal cord neurones in culture.
abstract: 1. The kinetic properties of the two most frequent conductance states of glycine receptor channels from somata of mouse spinal cord neurones in cell culture were investigated using the outside-out patch clamp technique. At low concentrations of glycine (0.5, 1 and 2 microM), single-channel currents were recorded with two predominant amplitudes corresponding to a dominant or main-conductance state of about 42 pS and a sub-conductance state of about 27 pS. Both conductance states opened singly and in bursts of several openings. Total current evoked and single-channel opening frequency increased as glycine concentration was increased from 0.5 to 2 microM. 2. For both conductance states mean open times were increased and open time frequency histograms were shifted to longer times as glycine concentration was increased from 0.5 to 2 microM. For both conductance states, three exponential components were required to fit best open time frequency distribution histograms at all glycine concentrations (0.5, 1 and 2 microM). The time constants of the exponential components for each conductance state were not significantly different across concentration, suggesting that the main- and sub-conductance states of the channel each opened into at least three open states. For the main-conductance state, the time constants were 1.09 +/- 0.09, 4.06 +/- 0.26 and 9.79 +/- 0.30 ms. For the sub-conductance state, the time constants were 0.55 +/- 0.04, 2.64 +/- 0.35 and 8.57 +/- 1.08 ms. The increase in long open times with concentration was due primarily to a shift in relative frequency of occurrence of openings from the shortest to the two longest open states. 3. Closed time frequency distributions of closures between main-conductance state openings, closures between sub-conductance state openings and closures between both main- and sub-conductance state openings were fitted with multiple exponential components, suggesting that the channel had several closed states. The two shortest time constants (0.16 +/- 0.01 and 1.26 +/- 0.13 ms) did not vary significantly with concentration (0.5-2 microM) or method of analysis. The longer time constant varied with concentration. 4. Bursts were defined as groups of openings surrounded by closures greater than a critical closed time. For both conductances states, mean burst durations were increased and burst duration frequency histograms were shifted to longer times as glycine concentration was increased from 0.5 to 2 miroM. Burst duration frequency histograms contained four exponential components for the main-conductance state and three exponential components for the sub-conductance state.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Neurology, University of Michigan Medical Center, Ann Arbor 48104.
authors.forename: R E
authors.initials: RE
authors.lastname: Twyman
authors.forename: R L
authors.initials: RL
authors.lastname: Macdonald
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism* / Q000502:physiology; D015640:Ion Channel Gating / Q000502:physiology; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D009474:Neurons / Q000378:metabolism*; D018009:Receptors, Glycine; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism*
chemical_list: D002712:Chlorides; D007473:Ion Channels; D018009:Receptors, Glycine; D017981:Receptors, Neurotransmitter; D005998:Glycine