DAMGO, a ${\mu}-Opioid$ Agonist and Cholecystokinin-Octapeptide Have Dual Modulatory Effects on Capsaicin-Activated Current in Rat Dorsal Root Ganglion Neurons

• Published in: The Korean journal of physiology & pharmacology Vol. 5; no. 1; pp. 71 - 78
• Main Authors: Eun, Su-Yong, Kim, Ji-Mok, Lee, Ji-Hye, Jung, Sung-Jun, Park, Joo-Min, Park, Yun-Kyung, Kim, Dong-Kwan, Kim, Sang-Jeong, Kwak, Ji-Yeon, Kim, Jun
• Format: Journal Article
• Language: Korean
• Published: 2001
• Subjects: Pain; Capsaicin; Opioids; Cholecystokinin; Dorsal root ganglion
• ISSN: 1226-4512; 2093-3827

Capsaicin, a pungent ingredient of hot pepper, elicits an intense burning pain when applied cutaneously and intradermally. Activation of capsaicin-gated channel in C-type dorsal root ganglion (DRG) neurons produces nonselective cationic currents. Although electrophysiological and biochemical properties of capsaicin-activated current $(I_{CAP})$ were studied, the regulatory mechanism and intracellular signaling pathway are still unclear. In the present study, we investigated the modulations of $I_{CAP}$ by DAMGO $({\mu}-opioid\;agonist)$ and cholecystokinin octapeptide (CCK-8). In 18 out of 86 cells, the amplitude of $I_{CAP}$ was significantly increased by DAMGO and completely reversed after washout, while $I_{CAP}$ was decreased by DAMGO in 25 cells. In 43 cells, DAMGO had no effect on $I_{CAP}$. Mean action potential duration was significantly different between 'increased-by-DAMGO' group and 'decreased-by-DAMGO' group. Mean amplitudes of $I_H$ were not significantly different between both groups. CCK-8 reversibly enhanced the amplitude of $I_{CAP}$ (5/13). DAMGO also increased $I_{CAP}$ amplitude significantly in the same cells. The amplitude of $I_{CAP}$ was increased in additive manner by combined applications of DAMGO and CCK-8 in these cells. These results suggest that DAMGO and CCK-8 can either increase or decrease $I_{CAP}$ presumably depending on the subtypes of DRG cells and classified by electrophysiological properties.