A comparison of the pharmacological properties of guinea-pig and human recombinant 5-HT4 receptors.
OBJECTIVE
5-HT(4) receptor agonists are used therapeutically to treat disorders of reduced gastrointestinal motility. Since such compounds are evaluated in guinea-pigs, we cloned, expressed and pharmacologically characterized the guinea-pig 5-HT(4) and human 5-HT(4(b)) splice variant, which share 95% homology. The functional properties of guinea-pig 5-HT(4(b)) receptors were compared with native receptors in guinea-pig colon.


METHODS
Membrane radioligand binding and whole cell cAMP accumulation assays were used to determine the affinities, potencies and intrinsic activities (IA). Contraction of the guinea-pig distal colon longitudinal muscle myenteric plexus preparation (LMMP) was monitored to evaluate functional activity.


RESULTS
pK(i) values for guinea-pig and human recombinant receptors, and guinea-pig striatum 5-HT(4) receptors, were in agreement, as were the potency and IA values for guinea-pig and human 5-HT(4) receptors expressed at a similar density ( approximately 0.2 pmol mg(-1) protein). Tegaserod was a potent (pEC(50)=8.4 and 8.7, respectively), full agonist at both guinea-pig and human 5-HT(4) receptors. In contrast, in the LMMP preparation, tegaserod was a potent, partial agonist (pEC(50)=8.2; IA=66%).


CONCLUSIONS
Close agreement between the pharmacological properties of guinea-pig and human 5-HT(4) receptors support the use of guinea-pig model systems for the identification of 5-HT(4) receptor therapeutics. However, the mechanisms underlying the different agonist properties of tegaserod in recombinant and isolated tissue preparations, and the extent to which these impact the clinical efficacy of tegaserod as a prokinetic agent, remain to be determined.
Vickery
R G
RG
Department of Molecular and Cell Biology, Theravance Inc., South San Francisco, CA 94080, USA. rvickery@@theravance.com
Mai
N
N
Kaufman
E
E
Beattie
D T
DT
Pulido-Rios
T
T
O'Keefe
M
M
Humphrey
P P A
PP
Smith
J A M
JA
D017398:Alternative Splicing; D000818:Animals; D001483:Base Sequence; D003106:Colon / Q000187:drug effects / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004064:Digestive System / Q000187:drug effects / Q000378:metabolism; D005765:Gastrointestinal Agents / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D044422:Receptors, Serotonin, 5-HT4 / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D058828:Serotonin 5-HT4 Receptor Agonists; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D017931:DNA Primers; D005765:Gastrointestinal Agents; D007211:Indoles; D012333:RNA, Messenger; D011994:Recombinant Proteins; D058828:Serotonin 5-HT4 Receptor Agonists; D017366:Serotonin Receptor Agonists; D044422:Receptors, Serotonin, 5-HT4; C105050:tegaserod