Table 1

Radioligand binding isotherms analyzed by Scatchard analysis for determination of cause for reduction in binding exhibited by mutant receptors

Transfected Cells	K_d	B_max	Relative B_max
	(nM ± S.E.)	(fmol/mg protein ± S.E.)	%
TPα	15.1 ± 1.9	2710 ± 416	100
TPα^N4–Q4	9.9 ± 0.65	1005 ± 405	43.5
TPα^N16–Q16	10.8 ± 1.9	1336 ± 493	60.2
TPα^{N4,N16–Q4,Q16}	11.4 ± 2.6	222 ± 50.2	8.2

HEK 293 cells were transiently transfected with the plasmids coding for the wild–type TPα or mutant TPα^N4–Q4, TPα^N16–Q16 and TPα^{N4,N16–Q4,Q16} receptors as indicated. For Scatchard analyses, radioligand binding assays on whole cells (75 μg/assay) were carried out in the presence of the TP antagonist [³H]SQ29,548 (50.4 Ci/mmol, 0–40nM). Radioligand binding data were analyzed with the INPLOT 4 computer program (GraphPad Software Inc.) to determine the K_d andB_max values. Data are presented as the mean values of four independent experiments ± standard error (S.E.). RelativeB_max values are expressed as percentage TP expression relative to levels of the wild-type TPα (% expression).