Bleached pigment activates transduction in isolated rods of the salamander retina.
1. We have used suction electrode recording together with rapid steps into Li+ solution and 0.5 mM IBMX solution to estimate the rates of the guanylyl phosphodiesterase (PDE) and guanylyl cyclase in isolated rods of the salamander, Ambystoma tigrinum. 2. We show that both the PDE and cyclase velocities are accelerated by steady background light. The steady velocities of both enzymes appear to be saturating functions of background intensity. 3. Bleaching also accelerates both the PDE and cyclase. This effect is maintained long after the bleaching stimulus is removed (up to 2 h) and is reversed only if the photopigment is regenerated with exogenous chromophore. 4. The estimated steady-state PDE and cyclase velocities appear to be linear functions of the amount of pigment bleached, as if each bleached pigment molecule activated the transduction cascade with the same probability and gain. 5. The effectiveness of bleached pigment in activating transduction is only 10(-6) to 10(-7) times that of activated rhodopsin (Rh*), but this is sufficient after large bleaches to produce an 'equivalent background' excitation of the rod, which is probably responsible, at least in part, for bleaching desensitization.
Cornwall
M C
MC
Department of Physiology, Boston University School of Medicine, MA 02118.
Fain
G L
GL
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000557:Ambystoma; D000818:Animals; D006162:Guanylate Cyclase / Q000378:metabolism; D066298:In Vitro Techniques; D017136:Ion Transport; D008027:Light; D008094:Lithium / Q000494:pharmacology; D008564:Membrane Potentials; D008954:Models, Biological; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D017299:Rod Opsins / Q000378:metabolism* / Q000528:radiation effects*; D015398:Signal Transduction / Q000528:radiation effects
D017299:Rod Opsins; D008094:Lithium; D010727:Phosphoric Diester Hydrolases; D006162:Guanylate Cyclase; D015056:1-Methyl-3-isobutylxanthine