Pflügers Archiv

, Volume 428, Issue 3–4, pp 372–381 | Cite as

Modulation of guanylate cyclase and phosphodiesterase by monovalent cations and nucleoside triphosphates in light-sensitive excised patches of rod outer segments

  • Eric A. Ertel
Excitable Tissues and Central Nervous Physiology

Abstract

Excised inside-out patches of vertebrate rod outer segment can support phototransduction. I have examined how ionic and metabolic conditions influence the functional properties of light-sensitive patches fromGekko gekko. I find that such patches retain a variable level of basal phosphodiesterase activity, which lowers the cyclic guanosine monophosphate (cGMP) concentration reaching the channels and reduces the dark current. The dose/response relationship for channel opening by cGMP varies among patches and this variability is only reduced by working in darkness with the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX), suggesting that it is only partially due to phosphodiesterase activity. MgATP or MgGTP, but not Mg or ATP separately, increase this activity but a kinase does not appear to be involved. Intracellular monovalent cations also influence dark current intensity and light response kinetics. With 5 mM MgGTP, 1 mM IBMX, and 144 mM Li+, Na+, K+, or Rb+, dark current intensity and recovery time follow the respective sequences K+>Rb+>Na+>Li+ and K+<Rb+<Li+<Na+. Without IBMX, a dark current develops with K+ but not with Na+. These effects are not due to altered channel permeability (P)\([P_{Li} + : _{Na} + : _K + : _{Rb} + _{: guanidinium)} /P_{Na} +\) = 0.84∶1.00∶ 1.01∶1.09∶0.42], or differential Mg2+ block, but to modulation of guanylate cyclase, which overcomes phosphodiesterase when the major cation is K+ but not when it is Na+.

Key words

Photoreceptors Vertebrates Rods and cones Monovalent cations Guanylate cyclase 3′,5′-Cyclic GMP Phosphodiesterase Guanosine triphosphate Adenosine triphosphate 

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Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • Eric A. Ertel
    • 1
  1. 1.Department of Physiology and BiophysicsUniversity of WashingtonSeattleUSA

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