Ultrastructural localization of gustducin immunoreactivity in microvilli of type II taste cells in the rat.

Gustducin is a transducin-like G protein (guanine nucleotide-binding protein) that is expressed in taste bud cells. Gustducin is believed to be involved in bitter and possibly sweet taste transduction. In the present study, we demonstrate that a subset of type II cells displays immunoreactivity to antisera directed against gustducin in taste buds of rat circumvallate papilla. Immunogold particles are present both in the microvilli and cytoplasm of the immunoreactive cells. Quantitative analysis of the data suggests that the number of colloidal gold particles (P<0.001) and nanogold particles (P<0.01) in the immunoreactive type II cells are much greater than in type I cells. There are also approximately 2.5 times (P<0.05) as many colloidal gold particles associated with the microvilli versus the cytoplasm in the immunoreactive type II cells. The ultrastructural distribution of gustducin immunoreactivity is consistent with its proposed role in the initial events of sensory transduction by gustatory receptor cells.