Abstract
Application of serotonin (5-HT) 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 was gradually and irreversibly depressed after intracellular injection of Clostridium difficile toxin B, which is known to mono-glucosylate and inactivate all Rho family 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 its effectors, irreversibly depressed the 5-HT-induced response. 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-induced current response or resting membrane. These results suggest that the 5-HT-induced Na+-current response may be facilitated by the activation of monomeric G-protein RhoA. [Jpn J Physiol 54 Suppl:S148 (2004)]
