Purpose: Characterize rod sensitivity and recovery kinetics in NH2OH. Method: The inner segments of salamander rods were drawn into suction pipettes, and photoresponses to flashes producing from 10 to 20,000 photoisomerizations (Φ) measured 10 s (or longer) after rapid jumping the outer segment (o.s.) into either Ca2+-clamping choline solution 1 (CS) or isotonic hydroxylamine solution (HA) at pH=7.5 or 6.0. Results: The hydroxylammonium ion NH3OH+ readily permeates the cGMP-channel, and from the integrated inward current during exposure to HA we estimate [NH2OH]i to reach 1-2 mM after 10 s exposure at pH=7.5, and, to exceed 7 mM after 10 s exposure at pH=6. Responses to subsaturating flashes in HA were similar in shape to those in CS, but HA decreased sensitivity (fraction current suppressed per Φ) 3- to 7-fold in a concentration-dependent manner. In contrast, the dominant time constant of recovery (τc ; estimated from the delay in recovery per e-fold change in Φ) was not affected by HA: τc (CS)= 2.46 ± 0.24 s vs. τc (HA) = 2.59 ± 0.36 s. Because HA decreases the lifetime of Metarhodopsin II, even in the presence of a normal complement of G-protein2, our results reject the hypothesis that τc is determined by the lifetime of R*. We demonstrate, by application of a model of activation and recovery of the rod G-protein cascade (for constant Ca2+ i) 1 that response kinetics in both HA and CS are consistent with the hypothesis that the dominant time constant, τc , is determined by the lifetime of the G1z-PDE (G*-PDE*) complex.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
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