The amplified P‐signal, an extremely photosensitive light scattering signal from rod outer segments, which is not affected by pre‐activation of phosphodiesterase with Gα‐GTP‐γ‐S

A light scattering signal from bovine rod outer segments in the presence of GTP is described. It has the same angular dependence as the P‐signal but is 3 orders of magnitude more sensitive to light and therefore we have called in the amplified P‐signal. Adding Gα‐GTP‐γ‐S has no significant effect on the light scattering signal despite the activation of PDE. cGMP affects the amplified P‐signal, but subsequent addition of Gα‐GTP‐γ‐S restores the normal signal character. All these facts strongly support the view that the amplified P‐signal reflects G‐protein activation rather than that of PDE. This is in striking contrast to an interpretation of a very similar light scattering signal previously described by other groups.