Excess Gβ Suppresses Spontaneous Activity

Science's STKE  15 Nov 2005:
Vol. 2005, Issue 310, pp. tw407
DOI: 10.1126/stke.3102005tw407

Elia et al. explored the mechanism by which Drosophila melanogaster photoreceptor cells maintain a low spontaneous activation rate, thereby allowing these cells to detect single photons of light. Using flies hypomorphic for Gβe and Gαq, the authors determined that decreased abundance of Gβe did not cause a decrease in the abundance of Gαq and vice versa. However, decreased abundance of Gβe decreased the fraction of Gαq attached to the plasma membrane and targeted to the phototransduction compartment, the rhabdomere. Nearly complete loss of Gαq prevented Gβγ from binding to the plasma membrane but did not disrupt targeting to the rhabdomere. Gβe was present at a concentration about 2.5 times that of Gαq, and the excess was present in the cytosol in the rhabdomere; approximately equal amounts of Gαq and Gβe were present in the membrane of dark-adapted flies. The hypomorphic Gβe alleles showed selective loss of the soluble Gβe pool. Whole-cell patch clamp analysis of the photoreceptor cells showed that cells with decreased Gβe exhibited higher spontaneous inward currents. In flies in which both Gβe and Gαq were decreased--thus restoring the proper ratio of Gβe to Gαq--spontaneous activity of the photoreceptor cells was similar to that of wild-type cells. Thus, excess Gβe in the cytosol of the rhabdomere interacting with Gαq, which translocates partially from the membrane to the cytosol during stimulation by light, appears to control the spontaneous activity of these cells.

N. Elia, S. Frechter, Y. Gedi, B. Minke, Z. Selinger, Excess of Gβe over Gqαe in vivo prevents dark, spontaneous activity of Drosophila photoreceptors. J. Cell Biol. 171, 517-526 (2005). [Abstract] [Full Text]