Abstract
Application of either serotonin (5-HT) or dopamine (DA) induces a slow Na+-current response in the identified neurons of Aplysia ganglia under voltage clamp. We previously reported that this type of response is produced by the activation of cholera toxin-sensitive G-protein. The Na+-current response to 5-HT or DA was gradually and irreversibly depressed after intracellular injection of Clostridium difficile toxin A or toxin B, which are known to mono-glucosylate and inactivate all Rho family G-proteins RhoA-C, Rac and Cdc42. Furthermore, intracellular injection of Clostridium botulinum exoenzyme C3, which is known to specifically ADP-ribosylate the monomeric G-protein, RhoA-C, and uncouple their effectors, irreversibly depressed both the 5-HT- and DA-induced responses. In contrast, intracellular injection of L63RhoA, a constitutively active form of RhoA, significantly augmented the 5-HT-induced response without affecting the resting membrane. Application of active form of Rac, or Cdc42 in the Rho-family G-protein did not have any effect either on the 5-HT- and DA-induced current responses or on the resting membrane. However, intracellular application of inhibitors for Rho-dependent kinase did not have any significant effect at all. These results suggest that both the 5-HT- and DA-induced Na+-current responses may be commonly facilitated by the activation of monomeric G-protein RhoA. [Jpn J Physiol 55 Suppl:S145 (2005)]
