The alpha subunit of the heterotrimeric G stimulatory protein (Gsa), encoded by the guanine nucleotide binding protein, alpha stimulating gene (Gnas, in mice), is expressed ubiquitously and mediates receptor-stimulated production of cyclic adenosine monophosphate (cAMP) and activation of the protein kinase A signaling pathway. We investigated the roles of Gsa in vivo in smooth muscle cells of mice.