Immunohistochemical expression of G protein α-subunit isoforms in rat and monkey Merkel cell-neurite complexes

Abstract.

The true function of Merkel cells (MCs) is still enigmatic, though the localization of various kinds of neurotransmitter-like substances in MCs has been revealed by immunohistochemistry. Most of the neurotransmitters act on target cells via seven-transmembrane receptors coupled to heterotrimeric G proteins. The heterotrimeric G proteins include various subfamilies that contribute to different signal transduction pathways. Therefore investigation of specific types of G proteins in MCs and related axon terminals (MC-axon terminals) should contribute to the elucidation of the function of MCs. In this study, we investigated the expression patterns of α-subunit isoforms of G proteins in MC-neurite complexes of the rat and monkey by enzymatic and fluorescence immunohistochemistry. MC-axon terminals of the rat and monkey showed positive immunoreactions of Gαo and Gαi1. Those of the monkey also showed a weak immunoreaction of Gαs. On the other hand, MCs of both animals showed positive immunoreactions of Gαo, Gαi1, Gαq, and Gαz. In addition, MCs of the monkey showed weak immunoreactions of Gαs. Gαo- and Gαi1-like immunoreactions in the MC-axon terminals suggest that MCs suppressively regulate receptive functions of type I mechanosensory nerve terminals. On the other hand, the localization of Gα-subunits in MCs suggests that these cells are regulated with hormones, neurotransmitter-like substances, or growth factors.