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. 1985 Apr;361:205–217. doi: 10.1113/jphysiol.1985.sp015641

Membrane current noise in toad retinal rods exposed to low external calcium.

G Matthews
PMCID: PMC1192855  PMID: 2580975

Abstract

Outer segment membrane current of single rod photoreceptors from toad retina was recorded with a suction electrode, and extracellular calcium concentration was manipulated by transferring the recorded cell from one pool of saline to another or by locally perfusing the outer segment. The large increase in dark current that resulted from exposure to low-calcium saline was accompanied by an increase in dark noise in the band 1-800 Hz. This noise was suppressed by bright light, and its power spectrum could be described by a single Lorentzian equation with average corner frequency of 40.1 +/- 9.5 Hz (mean +/- S.D., n = 11). In low-calcium saline, saturating flash responses were often followed by a transient increase in the dark current lasting 30-100 s. During this rebound period of increased dark current, increased dark noise similar to that described in 2 was observed. The power spectrum of this noise was also fitted by a single Lorentzian equation, with corner frequency averaging 29.7 +/- 6.6 Hz (mean +/- S.D., n = 27). To examine the possible role of intracellular voltage fluctuations in generating the noise, suction electrodes were filled with calcium-free saline and recordings were made from outer segments of rods attached to pieces of retina. In this recording configuration, the electrical coupling among the rods in the piece should attenuate voltage fluctuations associated with the post-light rebound period of increased dark current. In this situation, the rebound increase in dark current was still observed, but the noise was reduced or absent. Using the same recording configuration, isolated rods showed pronounced noise during the rebound. The result in 4 suggests that the noise resulted from fluctuations in intracellular voltage, not directly from fluctuations in the light-sensitive channels. In this view, the corner frequency of the noise power spectrum probably reflects the membrane time constant of the isolated rod.

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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. Bader C. R., Bertrand D., Schwartz E. A. Voltage-activated and calcium-activated currents studied in solitary rod inner segments from the salamander retina. J Physiol. 1982 Oct;331:253–284. doi: 10.1113/jphysiol.1982.sp014372. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Bastian B. L., Fain G. L. The effects of low calcium and background light on the sensitivity of toad rods. J Physiol. 1982 Sep;330:307–329. doi: 10.1113/jphysiol.1982.sp014343. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Baylor D. A., Hodgkin A. L. Detection and resolution of visual stimuli by turtle photoreceptors. J Physiol. 1973 Oct;234(1):163–198. doi: 10.1113/jphysiol.1973.sp010340. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Baylor D. A., Lamb T. D. Local effects of bleaching in retinal rods of the toad. J Physiol. 1982 Jul;328:49–71. doi: 10.1113/jphysiol.1982.sp014252. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Baylor D. A., Lamb T. D., Yau K. W. The membrane current of single rod outer segments. J Physiol. 1979 Mar;288:589–611. [PMC free article] [PubMed] [Google Scholar]
  7. Baylor D. A., Matthews G., Nunn B. J. Location and function of voltage-sensitive conductances in retinal rods of the salamander, Ambystoma tigrinum. J Physiol. 1984 Sep;354:203–223. doi: 10.1113/jphysiol.1984.sp015372. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Baylor D. A., Matthews G., Yau K. W. Two components of electrical dark noise in toad retinal rod outer segments. J Physiol. 1980 Dec;309:591–621. doi: 10.1113/jphysiol.1980.sp013529. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Fain G. L., Quandt F. N., Bastian B. L., Gerschenfeld H. M. Contribution of a caesium-sensitive conductance increase to the rod photoresponse. Nature. 1978 Mar 30;272(5652):466–469. doi: 10.1038/272467a0. [DOI] [PubMed] [Google Scholar]
  10. Hagins W. A., Yoshikami S. Proceedings: A role for Ca2+ in excitation of retinal rods and cones. Exp Eye Res. 1974 Mar;18(3):299–305. doi: 10.1016/0014-4835(74)90157-2. [DOI] [PubMed] [Google Scholar]
  11. Hodgkin A. L., McNaughton P. A., Nunn B. J., Yau K. W. Effect of ions on retinal rods from Bufo marinus. J Physiol. 1984 May;350:649–680. doi: 10.1113/jphysiol.1984.sp015223. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. 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]
  13. Liebman P. A., Mueller P., Pugh E. N., Jr Protons suppress the dark current of frog retinal rods. J Physiol. 1984 Feb;347:85–110. doi: 10.1113/jphysiol.1984.sp015055. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Neher E., Stevens C. F. Conductance fluctuations and ionic pores in membranes. Annu Rev Biophys Bioeng. 1977;6:345–381. doi: 10.1146/annurev.bb.06.060177.002021. [DOI] [PubMed] [Google Scholar]
  15. Torre V. The contribution of the electrogenic sodium-potassium pump to the electrical activity of toad rods. J Physiol. 1982 Dec;333:315–341. doi: 10.1113/jphysiol.1982.sp014456. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Yau K. W., McNaughton P. A., Hodgkin A. L. Effect of ions on the light-sensitive current in retinal rods. Nature. 1981 Aug 6;292(5823):502–505. doi: 10.1038/292502a0. [DOI] [PubMed] [Google Scholar]

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