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The effect of temperature on the GABA‐induced chloride current in isolated sensory neurones of the frog
Author(s) -
FfrenchMullen J.M.H.,
Tokutomi Naofumi,
Akaike Norio
Publication year - 1988
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1988.tb11701.x
Subject(s) - chemistry , kinetics , time constant , inhibitory postsynaptic potential , gamma aminobutyric acid , chloride , biophysics , reaction rate constant , atmospheric temperature range , biochemistry , endocrinology , receptor , thermodynamics , biology , organic chemistry , physics , quantum mechanics , electrical engineering , engineering
1 The effect of temperature on the kinetics of the activation and inactivation phases of γ‐aminobutyric acid (GABA)‐induced Cl − current (I Cl ) was examined in frog isolated sensory neurones. 2 The peak I Cl was reversibly reduced on changing the temperature and temperature‐dependent coefficients were shown to exist, with the highest Q 10 (1.58) occurring between 5–15°C. 3 At both room temperature (20°C) and 10°C, the GABA dose‐response curve was sigmoidal with a Hill coefficient of 2 and half‐maximal responses to GABA, K d , of 1.3 × 10 −5 m and 1.1 × 10 −5 m , respectively. Thus, indicating no change in the binding affinity of GABA when the temperature was decreased. 4 At GABA concentrations greater than 10 −5 m , both the activation and inactivation phases of the GABA‐induced I Cl consisted of double exponentials, fast and slow components respectively, in the temperature range of 10 to 30°C. 5 The fast (ẗ af ) and slow (ẗ as ) activation time constants decreased with an increase in temperature and increased with a reduction in temperature. With an increased temperature, the reduction in peak I Cl was due to a reduction in the slow time constant with no significant change in the fast time constant. 6 Both the fast (T̈ IF ) and slow (ẗ is ) inactivation time constants were also increased by cooling to 10°C; heating to 30°C had little effect. 7 The concentration‐dependence (10 −5 to 10 −3 m ) of the slow activation (ẗ as ) and inactivation (ẗ is ) time constants was unaltered by the change in temperature. Similarly, the lack of concentration‐dependence shown by the fast activation (ẗ af ) and inactivation (T̈ IF ) time constants was unaltered by the temperature change. 8 From recordings made with ‘inside‐out’ patches, the probability of opening of the GABA‐induced Cl − channels showed a marked increase with cooling to 10°C compared to room temperature (20°C), with no change in channel conductance. 9 The change in the GABA‐induced I Cl at different temperatures is, therefore, not due to changes in binding but to subsequent channel activation. Possible mechanisms whereby this occurs are discussed.