Light‐ and nucleotide‐dependent increase in apparent viscosity in a suspension of retinal disks

Abstract

Light triggers the cyclic nucleotide cascade in photoreceptor disk membranes. We report here that lightinduced changes in the apparent viscosity of disk membrane suspensions can also be observed using either native disk membranes or washed membranes reconstituted with G protein and PDE. The viscosity changes are light-and GTP-dependent and require the presence of G protein and PDE. The magnitude of the viscosity change increases with increasing membrane concentration. Under the same conditions in which light elicits a change in viscosity, we observe a large increase in light scattering by the disk membrane suspension.

Light‐induced Infrared Light Scatteringsignal in the Retina: Effect of Phosphodiesterase Inhibitors

“…This signal required not only G protein and GTP but also phosphodiesterase (PDE) and was enhanced by guanosine cyclic 3'5'monophosphate (cGMP), or PDE inhibitors like 3-isobutyl-1-methyl-xanthine (IBMX). In addition, increased PDE binding to disk membranes (Carettta and Stein, 1986) and increased apparent viscosity in the disk suspensions were observed (Caretta and Stein, 1987). Although at this stage a correlation between in vitro and in vivo light scatter signals may be premature, we would like to point out that the following observations are in agreement with Pepperberg et al (1988): the initial rapid IR light scattering decrease presents a waveform compatible with the light and GTP-dependent decrease in IR light scattering of disk membrane suspensions first observed by Bignetti et al (1980) and attributed by Kuhn et al (1981) to the dissociation of the G protein from disk membranes.…”