Functional characterization of alternatively spliced 5-HT sub(2) receptor isoforms from the pharynx and muscle of the parasitic nematode, Ascaris suum

• Published in: Journal of neurochemistry Vol. 83; no. 2; pp. 249 - 258
• Main Authors: Huang, X, Xiao, H, Rex, E B, Hobson, R J, Messer, WS Jr, Komuniecki, PR, Komuniecki, R W
• Format: Journal Article
• Language: English
• Published: 01.10.2002
• ISSN: 0022-3042

Serotonin (5-HT) receptors play key regulatory roles in nematodes and alternatively spliced 5-HT sub(2) receptor isoforms have been identified in the parasitic nematode, Ascaris suum. 5-HT sub(2As1) and 5-HT sub(2As2) contain different C-termini, and 5-HT sub(2As1 Delta 4) lacks 42 ammo acids at the C-terminus of the third intracellular loop. 5-HT sub(2As1) and 5-HT sub(2As2) exhibited identical pharmacological profiles when stably expressed in human embryonic kidney (HEK) 293 cells. Both 5-HT sub(2As) isoforms had higher affinity for 5-HT than their closely related Caenorhabditis elegans homolog (5-HT sub(2Ce)). This increased 5-HT affinity was not related to the substitution in 5-HT sub(2As1) of F sub(120) for Y in the highly conserved DRY motif found in the second intracellular loop of other 5-HT receptors, since a 5-HT sub(2As1) F sub(120) Y mutant actually exhibited increased 5-HT affinity compared with that of 5-HT sub(2As1). As predicted, cells expressing either 5-HT sub(2As1) or 5-HT sub(2As2) exhibited a 5-HT-dependent increase in phosphatidylinositol (PI) turnover. In contrast, although 5-HT sub(2As1 Delta 4) displayed a 10-fold higher affinity for 5-HT and 5-HT agonists than either 5-HT sub(2As1) or 5-HT sub(2As2), 5-HT sub(2As1 Delta 4) did not couple to either PI turnover or adenyl cyclase activity. Based on RT-PCR, 5-HT sub(2As1) and 5-HT sub(2As2) were more highly expressed in pharynx and body wall muscle and 5-HT sub(2As1 Delta 4) in nerve cord/hypodermis. This is the first report of different alternatively spliced 5-HT sub(2) receptor isoforms from any system.