Pflügers Archiv

, Volume 412, Issue 3, pp 240–247 | Cite as

Kinetic analysis of acetylcholine-induced chloride current in isolatedAplysia neurones

  • Yoshimi Ikemoto
  • Norio Akaike
Excitable Tissues and Central Nervous Physiology

Abstract

(1) Kinetics of activation and desensitization phases of the ACh-induced chloride current (ICl) were studied in isolated single neurones ofAplysia kurodai, using the ‘concentration clamp’ technique which combines internal perfusion and rapid exchange of the external solution within a few milliseconds (2) The dose-response curve for the peakICl gave a dissociation constant of 6.7×10−6 M a Hill coefficient of 1.7. (3) The current-voltage relationship was linear in the voltage range examined (−70to +30mV). The reversal potential (EACh) was −7.1±1.8mV (n=14). The value was close to the calculated equilibrium potential for chloride ions (ECl) (4) The activation phase of theICl was single exponential and the desensitization proceeded double exponentially to a steady state level. The time constants of both phases decreased with increasing concentrations of ACh but showed no potential dependency. The desensitizing component of theICl was generated by activation of a single population of the receptor-channel complex. (5) The recovery from desensitization of theICl induced, by 6×10−6 M ACh proceeded double exponentially, with time constants of 6.5 and 43 s at a holding potential of −30 mV. (6) Noise analysis performed on the steady state ofICl induced by low concentrations of ACh (3×10−7 M to 3×10−6 M) showed that the steadyICl was due to activation of a single population of the receptor-channel complex with a single channel conductance of 23.3±4.3 pS (n=9). (7) The closing (α) and opening [β'(A)] rate constants in a simple sequential model were obtained in the low concentration range of ACh. α was not altered by changing the ACh concentration [ACh]. The slope of the β'(A)-[ACh]relationship gave the Hill coefficient of 1.8 for the steady stateICl. The α-[ACh] and the β'(A)-[ACh] plots crossed at 2.4×10−6 M ACh, yielding theKD value. (8) Our results suggest that the ACh-inducedICl inAplysia neurones consists at least of two components: a minor-desensitizing component to form the steady stateICl and a desensitizing component which contributes to the peakICl. The receptor-channel complexes apparently have two binding sites for ACh.

Key words

IsolatedAplysia neurone Acetylcholine Chloride current Kinetics Activation Desensitization Noise analysis Concentration clamp technique 

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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Yoshimi Ikemoto
    • 1
  • Norio Akaike
    • 1
  1. 1.Department of Physiology, Faculty of MedicineKyushu UniversityFukuokaJapan

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