Cyclic GMP diffusion coefficient in rod photoreceptor outer segments

Y. Koutalos, K. Nakatani, King-Wai Yau

Research output: Contribution to journalArticle

Abstract

Cyclic GMP (cGMP) is the intracellular messenger that mediates phototransduction in retinal rods. As photoisomerizations of rhodopsin molecules are local events, the longitudinal diffusion of cGMP in the rod outer segment should be a contributing factor to the response of the cell to light. We have employed the truncated rod outer segment preparation from bullfrog (Rana catesbeiana) and tiger salamander (Ambystoma tigrinum) to measure the cGMP diffusion coefficient. In this preparation, the distal portion of a rod outer segment was drawn into a suction pipette for measuring membrane current, and the rest of the cell was then sheared off with a glass probe, allowing bath cGMP to diffuse into the outer segment and activate the cGMP-gated channels on the surface membrane. Addition and removal of bath cGMP were fast enough to produce effectively step changes in cGMP concentration at the open end of the outer segment. When cGMP hydrolysis is inhibited by isobutyl-methylxanthine (IBMX), the equation for the diffusion of cGMP inside the truncated rod outer segment has a simple analytical solution, which was have used to analyze the rise and decay kinetics of the cGMP-elicited currents. From these measurements we have obtained a cGMP diffusion coefficient of ~70 x 10-8 cm2 s-1 for bullfrog rods and ~60 x 10-8 cm2 s-1 for tiger salamander rods. These values are six to seven times lower than the expected value in aqueous solution. The estimated diffusion coefficient is the same at high (20-1000 μM) and low (5-10 μM) concentrations of cGMP, suggesting no significant effect from buffering over these concentration ranges.

Original languageEnglish (US)
Pages (from-to)373-382
Number of pages10
JournalBiophysical Journal
Volume68
Issue number1
StatePublished - 1995

Fingerprint

Rod Cell Outer Segment
Retinal Rod Photoreceptor Cells
Cyclic GMP
Ambystoma
Rana catesbeiana
Baths
Light Signal Transduction
Rhodopsin
Membranes
Suction
Glass
Hydrolysis

ASJC Scopus subject areas

  • Biophysics

Cite this

Cyclic GMP diffusion coefficient in rod photoreceptor outer segments. / Koutalos, Y.; Nakatani, K.; Yau, King-Wai.

In: Biophysical Journal, Vol. 68, No. 1, 1995, p. 373-382.

Research output: Contribution to journalArticle

Koutalos, Y. ; Nakatani, K. ; Yau, King-Wai. / Cyclic GMP diffusion coefficient in rod photoreceptor outer segments. In: Biophysical Journal. 1995 ; Vol. 68, No. 1. pp. 373-382.
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