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

The true function of Merkel cells (MCs) is still enigmatic, though the loca lization of various kinds of neurotransmitter-like substances in MCs has be en revealed by immunohistochemistry. Most of the neurotransmitters act on t arget cells via seven-transmembrane receptors coupled to heterotrimeric G p roteins. The heterotrimeric G proteins include various subfamilies that con tribute 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 alpha -subunit isofo rms of G proteins in MC-neurite complexes of the rat and monkey by enzymati c and fluorescence immunohistochemistry. MC-axon terminals of the rat and m onkey showed positive immunoreactions of G alphao and G alpha i1. Those of the monkey also showed a weak immunoreaction of G alphas. On the other hand , MCs of both animals showed positive immunoreactions of G alphao, G alpha i1, G alphaq, and G alphaz. In addition, MCs of the monkey showed weak immu noreactions of G alphas. G alphao-and G alpha il-like immunoreactions in th e MC-axon terminals suggest that MCs suppressively regulate receptive funct ions of type I mechanosensory nerve terminals. On the other hand, the local ization of G alpha -subunits in MCs suggests that these cells are regulated with hormones, neurotransmitter-like substances, or growth factors.