Heterotrimeric G proteins mediate cellular responses to receptor stimulation including regulated exocytosis. Galphaz, a member of the Galphai family, is expressed at low levels in neurons and other secretory cells and has been suggested to regulate secretion. However, Galphaz- hydrolyzes GTP far more slowly than rapid secretory responses. Our lab has identified two proteins that accelerate 61P hydrolysis by Galpha2z; RGSZ1 and RGSZ2. This interaction between RGSZ isoforms may be requisite for the physiological role of Galphaz in vivo. To test this hypothesis, the functional interactions between Galpha and RGSZ1 and Z2 will be explored. First, neural and neuroendocrine tissue expression of RGSZ isoforms relative to Galphaz expression will be investigated in: l) wild type mice, 2) mice that are deficient in Galphaz or 3) mice that express a constitutively active form of Go:- via a DBH-promoter based transgene. Next, the intracellular distribution of RGSZ1 and Z2 relative to Galpha will also be investigated: l) in cells that endogenously express Galphaz and RGSZ isoforms and 2) in cells that have been transfected with these proteins. Finally, the effects Galphaz and RGSZ proteins on stimulated catecholamine release will be examined in chromaffin cells from wild type, Galphaz knockout, and Galphaz mutant mice.
