Direct activation of cGMP-dependent channels of retinal rods by the cGMP phosphodiesterase

Proc Natl Acad Sci U S A. 1989 May;86(10):3634-8. doi: 10.1073/pnas.86.10.3634.

Abstract

The cationic conductances of purified bovine retinal rod membranes were studied by incorporation of vesicles into planar lipid bilayers. When the membranes were stripped of all peripheral proteins [guanine nucleotide-binding protein (G protein) and cGMP phosphodiesterase (3',5'-cyclic-GMP 5'-nucleotidohydrolase), EC 3.1.4.35], sodium and calcium fluxes were almost only observed in the presence of cGMP. Reconstitution experiments in which purified cGMP phosphodiesterase alone or with G protein were reassociated to the vesicles in proportions similar to those found in the native rod provide evidence for a direct interaction between the cGMP-dependent channel protein and the phosphodiesterase. (i) In its inhibited state, phosphodiesterase markedly stimulates the activity of the channels in the presence of cGMP (situation in the dark-adapted rod) but is not capable of activating the channels in the absence of cGMP. (ii) In the absence of cGMP, activation of the phosphodiesterase by G protein with GTP bound (equivalent to photoexcitation) induces the opening of cation channels that have the same conductance for sodium ions as cGMP-activated channels (20-22 pS, with two sublevels of about 7 pS and 13 pS).

MeSH terms

  • 3',5'-Cyclic-GMP Phosphodiesterases / physiology*
  • Animals
  • Cattle
  • Cyclic GMP / physiology*
  • Diltiazem / pharmacology
  • Electric Conductivity
  • GTP-Binding Proteins / physiology*
  • In Vitro Techniques
  • Ion Channels / physiology*
  • Membrane Potentials
  • Molecular Weight
  • Photoreceptor Cells / physiology*
  • Sodium / physiology

Substances

  • Ion Channels
  • Sodium
  • 3',5'-Cyclic-GMP Phosphodiesterases
  • GTP-Binding Proteins
  • Diltiazem
  • Cyclic GMP