Desensitization kinetics of a K+ acetylcholine response in Aplysia

J. Salánki, Martyn L. Evans, David O. Carpenter

Research output: Contribution to journalArticle

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Abstract

We have studied the process of acetylcholine receptor desensitization on Aplysia medial pleural neurons under voltage clamp conditions. Acetylcholine, applied by microperfusion, elicits a biphasic response on these neurons, a rapid component which reverses polarity at about -60 mV and is Cl-dependent, and a slower component which reverses at about -85 mV and is K-dependent. Both components show desensitization, and the present study focuses on the K-dependent component, which could be isolated by maintaining membrane potential at the Cl equilibrium potential or by blocking the Cl component pharmacologically. K-dependent acetylcholine responses on these neurons varied in regard to time to peak of response and rate of desensitization. While the rising phase of the response was always fitted by a single exponential process, times to peak were divided somewhat arbitrarily into three broad groups of fast (6 s.) Desensitization of fast responses was best described by two exponential processes plus a constant, medium responses by a double exponential, and slow responses by single exponential plus a constant. The apparent dissociation constant of acetylcholine was 17.3 ± 1.6 μM. The best fit of responses for a given cell remained constant over a range of acetylcholine doses, but the kinetics of both fast and slow components accelerated with dose and depolarization. The fast component of desensitization was very temperature dependent. In neurons where it was present it was abolished by cooling, while in neurons with no fast component at room temperature it would appear with warming. The time constant of the fast component varied inversely with temperature. The time constant of the slow component was maximal at 22-24 °C, and fell on either side of this temperature. These results suggest that receptor desensitization for acetylcholine K responses is, like Na-dependent responses, composed of two independent processes. When responses to the acetylcholine agonists, carbachol and arecoline, were compared to those of acetylcholine on fast-type neurons, the times to peak varied in the order acetylcholine <carbachol <arecoline. The carbachol response was best fitted by two exponential functions, while arecoline was best fitted by a single exponential plus a constant.

Original languageEnglish
Pages (from-to)298-308
Number of pages11
JournalBrain Research
Volume495
Issue number2
DOIs
Publication statusPublished - Aug 28 1989

Fingerprint

Aplysia
Acetylcholine
Arecoline
Neurons
Carbachol
Temperature
Cholinergic Receptors
Cholinergic Agonists
Membrane Potentials

Keywords

  • Acetylcholine
  • Aplysia
  • Desensitization
  • Potassium conductance

ASJC Scopus subject areas

  • Developmental Biology
  • Molecular Biology
  • Clinical Neurology
  • Neuroscience(all)

Cite this

Desensitization kinetics of a K+ acetylcholine response in Aplysia. / Salánki, J.; Evans, Martyn L.; Carpenter, David O.

In: Brain Research, Vol. 495, No. 2, 28.08.1989, p. 298-308.

Research output: Contribution to journalArticle

Salánki, J. ; Evans, Martyn L. ; Carpenter, David O. / Desensitization kinetics of a K+ acetylcholine response in Aplysia. In: Brain Research. 1989 ; Vol. 495, No. 2. pp. 298-308.
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