Two opposite effects of ATP on the apparent sensitivity of the cGMP-gated channel of the carp retinal cone

Vis Neurosci. 1997 Jul-Aug;14(4):609-15. doi: 10.1017/s0952523800012578.

Abstract

Effects of ATP on the activity of cGMP-gated channels from carp cone photoreceptors were studied. In 29% of the patches examined (N = 45), ATP (1 mM) enhanced a current evoked by cGMP (20 microM, up to about 100%), in 33%. ATP suppressed it by up to about 90%, and in the remaining 38%, ATP had no effect. ATP showed similar effects on a current evoked by 8-bromoguanosine 3',5'-cyclic monophosphate (2 microM, enhancing in 42% of the patches, suppressing in 25%, no effect in 33%, N = 12), suggesting that the effects were not through modulation of the phosphodiesterase. Both of the effects, enhancement and suppression, were produced by a change in apparent affinity for cGMP, since (1) the maximum current evoked by cGMP of the saturating concentration (> or = 1 mM) was not affected, and (2) the K1/2 value decreased by approximately 45% (N = 2) or increased by approximately 25% (N = 2). A lower pH (approximately 6) facilitated the enhancing effect. ATP-gamma-S (1 mM) showed a suppressing effect in 80% of the patches and no effect in 20% of the patches (N = 10). However, ATP-gamma-S did not show an enhancing effect. Thus, ATP had two opposite effects through different mechanisms on the apparent sensitivity of the channel to cGMP; increasing and decreasing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / analogs & derivatives
  • Adenosine Triphosphate / pharmacology*
  • Affinity Labels / pharmacology
  • Animals
  • Carps / physiology*
  • Cyclic GMP / pharmacology*
  • Dose-Response Relationship, Drug
  • Guanosine / analogs & derivatives
  • Guanosine / pharmacology
  • Hydrogen-Ion Concentration
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology*
  • Ion Channels / drug effects
  • Ion Channels / physiology*
  • Membrane Potentials / drug effects
  • Patch-Clamp Techniques
  • Retinal Cone Photoreceptor Cells / drug effects
  • Retinal Cone Photoreceptor Cells / metabolism*
  • Vision, Ocular / drug effects
  • Vision, Ocular / physiology

Substances

  • Affinity Labels
  • Ion Channels
  • Guanosine
  • adenosine 5'-O-(3-thiotriphosphate)
  • 8-bromoguanosine
  • Adenosine Triphosphate
  • Cyclic GMP