Skip to main content
PMC home page
Biophysical Journal logoLink to Biophysical Journal
. 1994 Jul;67(1):183–189. doi: 10.1016/S0006-3495(94)80468-0

Variance analysis of gamma-aminobutyric acid (GABA)-ergic inhibitory postsynaptic currents from melanotropes of Xenopus laevis.

J G Borst 1, K S Kits 1, M Bier 1
PMCID: PMC1225348  PMID: 7918986

Abstract

We have studied the variance in the decay of large spontaneous gamma-aminobutyric acid (GABA)-ergic inhibitory postsynaptic currents (IPSCs) in melanotropes of Xenopus laevis to obtain information about the number of GABAA receptor channels that bind GABA during the IPSCs. The average decay of the IPSCs is well described by the sum of two exponential functions. This suggests that a three-state Markov model is sufficient to describe the decay phase, with one of the three states being an absorbing state, entered when GABA dissociates from the GABAA receptor. We have compared the variance in the decay of large spontaneous IPSCs with the variance calculated for two different three-state models: a model with one open state, one closed state, and one absorbing state (I), and a model with two open states and one absorbing state (II). The data were better described by the more efficient model II. This suggests that the efficacy of GABA at synaptic GABAA receptor channels is high and that only a small number of channels are involved in generating the GABA-ergic IPSCs.

Full text

PDF
187

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Anderson C. R., Stevens C. F. Voltage clamp analysis of acetylcholine produced end-plate current fluctuations at frog neuromuscular junction. J Physiol. 1973 Dec;235(3):655–691. doi: 10.1113/jphysiol.1973.sp010410. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Bormann J., Clapham D. E. gamma-Aminobutyric acid receptor channels in adrenal chromaffin cells: a patch-clamp study. Proc Natl Acad Sci U S A. 1985 Apr;82(7):2168–2172. doi: 10.1073/pnas.82.7.2168. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Borst J. G., Lodder J. C., Kits K. S. Large amplitude variability of GABAergic IPSCs in melanotropes from Xenopus laevis: evidence that quantal size differs between synapses. J Neurophysiol. 1994 Feb;71(2):639–655. doi: 10.1152/jn.1994.71.2.639. [DOI] [PubMed] [Google Scholar]
  4. Busch C., Sakmann B. Synaptic transmission in hippocampal neurons: numerical reconstruction of quantal IPSCs. Cold Spring Harb Symp Quant Biol. 1990;55:69–80. doi: 10.1101/sqb.1990.055.01.009. [DOI] [PubMed] [Google Scholar]
  5. Colquhoun D., Sakmann B. Fast events in single-channel currents activated by acetylcholine and its analogues at the frog muscle end-plate. J Physiol. 1985 Dec;369:501–557. doi: 10.1113/jphysiol.1985.sp015912. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Dilger J. P., Brett R. S. Direct measurement of the concentration- and time-dependent open probability of the nicotinic acetylcholine receptor channel. Biophys J. 1990 Apr;57(4):723–731. doi: 10.1016/S0006-3495(90)82593-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Dudel J., Finger W., Stettmeier H. Inhibitory synaptic channels activated by gamma-aminobutyric acid (GABA) in crayfish muscle. Pflugers Arch. 1980 Sep;387(2):143–151. doi: 10.1007/BF00584265. [DOI] [PubMed] [Google Scholar]
  8. Edwards F. A., Konnerth A., Sakmann B., Takahashi T. A thin slice preparation for patch clamp recordings from neurones of the mammalian central nervous system. Pflugers Arch. 1989 Sep;414(5):600–612. doi: 10.1007/BF00580998. [DOI] [PubMed] [Google Scholar]
  9. Faber D. S., Young W. S., Legendre P., Korn H. Intrinsic quantal variability due to stochastic properties of receptor-transmitter interactions. Science. 1992 Nov 27;258(5087):1494–1498. doi: 10.1126/science.1279813. [DOI] [PubMed] [Google Scholar]
  10. Hestrin S., Sah P., Nicoll R. A. Mechanisms generating the time course of dual component excitatory synaptic currents recorded in hippocampal slices. Neuron. 1990 Sep;5(3):247–253. doi: 10.1016/0896-6273(90)90162-9. [DOI] [PubMed] [Google Scholar]
  11. Katz B., Miledi R. The statistical nature of the acetycholine potential and its molecular components. J Physiol. 1972 Aug;224(3):665–699. doi: 10.1113/jphysiol.1972.sp009918. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Lester R. A., Clements J. D., Westbrook G. L., Jahr C. E. Channel kinetics determine the time course of NMDA receptor-mediated synaptic currents. Nature. 1990 Aug 9;346(6284):565–567. doi: 10.1038/346565a0. [DOI] [PubMed] [Google Scholar]
  13. Macdonald R. L., Rogers C. J., Twyman R. E. Kinetic properties of the GABAA receptor main conductance state of mouse spinal cord neurones in culture. J Physiol. 1989 Mar;410:479–499. doi: 10.1113/jphysiol.1989.sp017545. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Newland C. F., Colquhoun D., Cull-Candy S. G. Single channels activated by high concentrations of GABA in superior cervical ganglion neurones of the rat. J Physiol. 1991 Jan;432:203–233. doi: 10.1113/jphysiol.1991.sp018382. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Ogden D. C., Colquhoun D. The efficacy of agonists at the frog neuromuscular junction studied with single channel recording. Pflugers Arch. 1983 Nov;399(3):246–248. doi: 10.1007/BF00656725. [DOI] [PubMed] [Google Scholar]
  16. Robinson H. P., Sahara Y., Kawai N. Nonstationary fluctuation analysis and direct resolution of single channel currents at postsynaptic sites. Biophys J. 1991 Feb;59(2):295–304. doi: 10.1016/S0006-3495(91)82223-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Sigworth F. J. The variance of sodium current fluctuations at the node of Ranvier. J Physiol. 1980 Oct;307:97–129. doi: 10.1113/jphysiol.1980.sp013426. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Sine S. M., Steinbach J. H. Activation of acetylcholine receptors on clonal mammalian BC3H-1 cells by low concentrations of agonist. J Physiol. 1986 Apr;373:129–162. doi: 10.1113/jphysiol.1986.sp016039. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Verburg-van Kemenade B. M., Tappaz M., Paut L., Jenks B. G. GABAergic regulation of melanocyte-stimulating hormone secretion from the pars intermedia of Xenopus laevis: immunocytochemical and physiological evidence. Endocrinology. 1986 Jan;118(1):260–267. doi: 10.1210/endo-118-1-260. [DOI] [PubMed] [Google Scholar]
  20. de Rijk E. P., van Strien F. J., Roubos E. W. Demonstration of coexisting catecholamine (dopamine), amino acid (GABA), and peptide (NPY) involved in inhibition of melanotrope cell activity in Xenopus laevis: a quantitative ultrastructural, freeze-substitution immunocytochemical study. J Neurosci. 1992 Mar;12(3):864–871. doi: 10.1523/JNEUROSCI.12-03-00864.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Biophysical Journal are provided here courtesy of The Biophysical Society

RESOURCES