Blocking effect of serotonin on inhibitory dopamine receptor activity of Aplysia ganglion cells.

Publisher Website
Google Scholar
Abstract
The abdominal ganglion of Aplysia includes neurons with a characteristic dopamine (DA) receptor, the activation of which induces a marked hyperpolarization with a specific increase in the permeability of the membrane to K+. The DA receptor of this type is called the HK-type. A 2-min exposure to 1 .mu.M serotonin (5-HT) had little effect on the resting membranes with the receptor of HK-type, but significantly depressed the responses to 10 .mu.M DA. The depressing effect of 5-HT on this type of response was completely reversible after a 15-min washing with normal artificial Aplysia blood. Lineweaver-Burke type plotting of the DA-induced respones showed a systematic shift of the straight lines when the concentration of 5-HT was increased; the slope of the line became steeper but the intercept on the ordinate remained unchanged. The dose-inhibition curves, in which relative responses to a given [DA] were plotted against log [5-HT], showed a parallel shift toward the right when the concentration of DA increased. 5-HT evidently competes with DA for common binding sites at the DA receptor of HK-type and the blockade is not due to the interaction of 5-HT with K+ channels in the receptor membrane. The effect of other indole derivatives suggests that the DA receptor of HK-type includes anionic and cationic sites to which the NH2 [amino] group and 5-HO [hydroxy] group of 5-HT could specifically bind, thus exhibiting competitive blockade.