Table 1.

Ligand binding to membrane preparations from control and transgenic hearts

	Line 1 hearts	Line 5 hearts	Control hearts
	Antagonist and agonist binding properties
[3H]CPX Bmax, fmol⋅mg−1	6,574 ± 965*	10,691 ± 1,002*†	8 ± 5
	(n = 15)	(n = 8)	(n = 11)
[3H]CPX Kd, nM	0.92 ± 0.09	1.12 ± 0.09	0.73 ± 0.17
	(n = 15)	(n = 8)	(n = 11)
125I-ABA Bmax, fmol⋅mg−1	475 ± 25	244 ± 8†	—
	(n=6)	(n=6)
% coupling‡	7.7 ± 1.0	2.4 ± 0.3†	—
	Ligand Ki values (n = 6 in all cases)
Theo, nM	17,000 ± 1,800	10,000 ± 2,200	—
CGS, nM	400 ± 200	200 ± 100	—
CPX, nM	0.4 ± 0.3	2.0 ± 0.6	—
CPA, nM	0.3 ± 0.2	0.3 ± 0.1	—

Total and coupled receptor number was assessed from the B_max for antagonist (CPX) and agonist (ABA), respectively. Agonist and antagonist K_i values were determined as described in Materials and Methods. Theo, theophylline; CGS, CGS21680; CPX, 8-cyclopentyl-1,3-dipropylxanthine; CPA, N⁶-cyclopentyladenosine. [³H]CPX and ¹²⁵I-ABA were used with competing antagonists and agonists, respectively. All binding studies were performed in triplicate. 

^*P < 0.05 transgenic vs. control. 

^†P < 0.05 line 5 vs. line 1. 

^‡Percent coupling is defined as B_max agonist/B_max antagonist.