Comprehensive study on G protein alpha-subunits in taste bud cells, with special reference to the occurrence of Galphai2 as a major Galpha species.

Previous studies have identified many cDNA species that encode a variety of G protein alpha-subunits occurring in taste buds. These include the cDNA encoding a taste-bud-specific Galpha, gustducin (G(gust)). Here we carried out comprehensive analyses of Galpha species that occur in the taste buds of rat circumvallate papillae and also in their single cells isolated from the taste buds. Reverse transcriptase-polymerase chain reaction showed the presence of 10 kinds of Galpha cDNAs, including a splice variant of Galphas, among which G(gust), Galphas, Galphai2 and Galphai3 cDNAs were shown to be major species. In situ hybridization and immunohistochemistry showed that Galphai2, as well as G(gust), expressed in a subset of taste bud cells, and the frequency of Galphai2-expression appears to be higher than that of G(gust). Southern analyses of the amplified cDNA from single cells showed that each taste bud cell expresses multiple Galpha mRNA species. For example, some Galphai2-positive cells also express one or more other Galpha species, including Galphas, Galphai3 and G(gust), and there is no apparent correlation in expression among the three Galpha species.