Effects of IBMX on the rod ERG of the isolated perfused cat eye: antagonism with light, calcium or L-cis-diltiazem.
Full-field electroretinograms (ERGs) were recorded from isolated cat eyes perfused through the ophthalmociliary artery with the cGMP-PDE inhibitor, 3-isobutylmethylxanthine (IBMX). Under dark-adapted conditions perfusion with IBMX resulted in reduced ERG b-wave amplitudes at low stimulus luminances and supernormal b-wave amplitudes at high stimulus luminances with reduced b-wave sensitivity; b-wave implicit times were more delayed at low than at high stimulus luminances. Presentation of a steady white background or high calcium fully reversed the supernormal amplitudes and partially reversed the delayed implicit times produced by IBMX. Rod ERG b-wave sensitivity, reduced with IBMX alone, was partially reversed with calcium but further reduced with background light. Perfusion with the cation channel blocker, L-cis-diltiazem, also reversed the supernormal amplitudes produced by IBMX but had no effect on implicit times or b-wave sensitivity. Possible mechanisms of action of these antagonists and clinical implications of these findings are considered.
Pawlyk
B S
BS
Berman-Gund Laboratory for the Study of Retinal Degenerations, Harvard Medical School, Massachusetts Eye & Ear Infirmary, Boston 02114.
Sandberg
M A
MA
Berson
E L
EL
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002415:Cats; D003623:Dark Adaptation; D004110:Diltiazem / Q000494:pharmacology*; D004596:Electroretinography / Q000187:drug effects; D066298:In Vitro Techniques; D008027:Light; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*
D004110:Diltiazem; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine