Differential desensitization properties of rat neuronal nicotinic acetylcholine receptor subunit combinations expressed in Xenopus laevis oocytes

Cell Mol Neurobiol. 1995 Aug;15(4):411-25. doi: 10.1007/BF02071877.


1. Chronic administration of nicotine up-regulates mammalian neuronal nicotinic acetylcholine receptors (nAChRs). A key hypothesis that explains up-regulation assumes that nicotine induces desensitization of receptor function. This is correlated with behaviorally expressed tolerance to the drug. 2. The present experiments were conducted to: (a) obtain information on the nicotine-induced desensitization of neuronal nAChR function, a less understood phenomenon as compared to that of the muscle and electric fish receptor counterparts; (b) test the hypothesis that different receptor subunit combinations exhibit distinct desensitization patterns. 3. Xenopus laevis oocytes were injected with mRNAs encoding rat receptor subunits alpha 2, alpha 3, or alpha 4 in pairwise combination with the beta 2 subunit. The responses to various concentrations of acetylcholine (ACh) or nicotine were analyzed by the two electrode voltage clamp technique. 4. Concentration-effect curves showed that nicotine was more potent than ACh for all the receptor subunit combinations tested. Only the alpha 4 beta 2 combination exhibited a depression of the maximum effect at concentrations higher than 20 microM nicotine. 5. After a single nicotine pulse, receptor desensitization (calculated as a single exponential decay) was significantly slower for alpha 4 beta 2 than for either alpha 3 beta 2 or alpha 2 beta 2. 6. Concentrations of nicotine that attained a near maximum effect were applied, washed, and re-applied in four minute cycles. The responses were calculated as percentages of the current evoked by the initial application. Following 16 minutes of this protocol, the alpha 4 beta 2 combination showed a greater reduction of the original response as compared to the alpha 2 beta 2 and alpha 3 beta 2 subunit combinations. Taking points 5 and 6 together, these experiments suggest that the alpha 4 beta 2 receptor subtype desensitizes at a slower rate and remains longer in the desensitized state. 7. Because alpha 4 beta 2 is the main receptor subunit combination within the brain and is up-regulated by nicotine, our data may be important for understanding the molecular basis of tolerance to this drug.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylcholine / pharmacology
  • Animals
  • Drug Tolerance / physiology
  • Egtazic Acid
  • Electrophysiology
  • Isotonic Solutions
  • Neurons / ultrastructure
  • Nicotine / pharmacology
  • Oocytes / physiology
  • Rats
  • Receptors, Nicotinic / physiology*
  • Receptors, Nicotinic / ultrastructure
  • Ringer's Solution
  • Sensitivity and Specificity
  • Up-Regulation / physiology
  • Xenopus laevis


  • Isotonic Solutions
  • Receptors, Nicotinic
  • Egtazic Acid
  • Nicotine
  • Ringer's Solution
  • Acetylcholine