Functional responses of human beta1 adrenoceptors with defined haplotypes for the common 389R>G and 49S>G polymorphisms.
OBJECTIVE
The human beta1-adrenoceptor (beta1-AR) is an important therapeutic target for cardiovascular diseases and has two common functional polymorphisms (49S>G and 389R>G). These polymorphisms have only been studied in isolation, however, and not in the context of the four haplotypes (SR, SG, GR and GG) that exist in native beta1-ARs.


METHODS
To address this, the function of each of the receptor haplotypes was studied in HEK 293 cells stably transfected with appropriately modified human beta1-adrenoceptor cDNA sequence.


RESULTS
The affinity for the beta-adrenoceptor ligand, [125I]-cyanopindolol, was not significantly different across the haplotypes, but a high affinity state for the beta1-AR could only be demonstrated for receptors carrying the 389R substitution. Both basal (GR 36.3 +/- 2.9* vs. SR 16.5 0 +/- 3.6 and GG 31.7 +/- 1.4* vs. SG 15.6 +/- 1.5 pmol/mg protein; *P < 0.001) and maximal (GR 163 +/- 7.6 vs. SR 124 +/- 8.1* and GG 75.0 +/- 1.0 vs. SG 52.4 +/- 1.1* pmol/mg protein; *P < 0.001) isoprenaline-evoked cAMP production was significantly affected by both substitutions. Incubation with isoprenaline (10 microm for 30 min or 20 h) caused increased down-regulation of beta1-ARs in cells expressing GG and GR haplotypes (at 20 h percentage fall respectively -28.1 +/- 5.2 and -38.2 +/- 3.0).


CONCLUSIONS
These data highlight important functional differences between the common beta1-AR haplotypes and the need for consideration of haplotypes and not individual genotypes in determining the in-vivo role of these polymorphisms within this important drug target.
Sandilands
Alastair
A
Clinical Pharmacology Unit, Level 6, Addenbrooke's Centre for Clinical Investigation, Addenbrooke's Hospital, Cambridge, CM6 2EE, UK.
Yeo
Giles
G
Brown
Morris J
MJ
O'Shaughnessy
Kevin M
KM
D058665:Adrenergic beta-1 Receptor Agonists; D058671:Adrenergic beta-1 Receptor Antagonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D015536:Down-Regulation; D005838:Genotype; D006239:Haplotypes / Q000235:genetics*; D006801:Humans; D007457:Iodine Radioisotopes; D007545:Isoproterenol / Q000494:pharmacology; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008024:Ligands; D010869:Pindolol / Q000031:analogs & derivatives* / Q000378:metabolism; D011110:Polymorphism, Genetic / Q000235:genetics*; D018342:Receptors, Adrenergic, beta-1 / Q000235:genetics*
D058665:Adrenergic beta-1 Receptor Agonists; D058671:Adrenergic beta-1 Receptor Antagonists; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D018076:DNA, Complementary; D007457:Iodine Radioisotopes; D008024:Ligands; D018342:Receptors, Adrenergic, beta-1; C047975:cyanopindolol; D010869:Pindolol; D000242:Cyclic AMP; D007545:Isoproterenol