Inward currents in neurons from newborn guinea pig intestine: mediation by 5-hydroxytryptamine type 3 receptors.
The whole-cell patch-clamp technique was used to analyze the effects of 5-hydroxytryptamine (5-HT) and alosetron on cultured myenteric neurons from newborn guinea pigs. All neurons responded to 5-HT (EC(50) approximately 38.7 microM) with a concentration-dependent inward current (reversal potential = 7.1 +/- 1.7 mV) with a short latency and rapid decay. Because the 5-HT-induced inward current was mimicked by 2-methyl-5-hydroxytryptamine (50 microM) and blocked by ondansetron (5.0 microM) and MDL 72222 (0.05 microM), it was 5-HT(3)-mediated. Alosetron blocked (IC(50) approximately 0.05 microM; Hill coefficient approximately 1.24) the 5-HT- and 2-methyl-5-hydroxytryptamine-induced inward currents. This effect was independent of membrane potential and was not seen when alosetron was delivered to the inside of cells. Alosetron-sensitive sites are, thus, accessible only on the ectodomain of the plasmalemma. The effect of alosetron was reversible, but not surmountable. Although nicotine (100 microM) mimicked the 5-HT-induced inward current, the response was antagonized by hexamethonium (100 microM), but not by alosetron, implying its potential to be a selective 5-HT(3) antagonist. Hexamethonium did not affect responses to 5-HT. Most neurons in the cultures were 5-HT-immunoreactive and immunostained with an antibody raised against 5-HT(3) receptors. The 5-HT-selective uptake inhibitor, fluoxetine (30 microM), gradually reduced the amplitude of the current induced by 5-HT; the residual response was abolished by alosetron (0.2 microM). The effect of fluoxetine could have been caused by either the desensitization of 5-HT(3) receptors or by a nonspecific 5-HT(3) antagonistic effect of fluoxetine. It is concluded that alosetron is a potent and noncompetitive 5-HT(3) antagonist on myenteric neurons.
Zhai
J
J
Department of Anatomy and Cell Biology, Columbia University, New York, New York, USA. Jin_Zhai@Lilly.com
Gershon
M D
MD
Walsh
J H
JH
Wong
H C
HC
Kirchgessner
A L
AL
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002243:Carbolines / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005724:Ganglia / Q000187:drug effects / Q000502:physiology; D006168:Guinea Pigs; D007422:Intestines / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology
D002243:Carbolines; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists; C090840:alosetron; D012701:Serotonin; C045918:2-methyl-5-HT; D000109:Acetylcholine