TABLE 2

Inhibition constants (K_i) of Gly-Sar and seven ACE inhibitors for the inhibition of [¹⁴C]Gly-Sar uptake in HRPE-hPEPT1 and HRPE-hPEPT2 cells Uptake of [¹⁴C]Gly-Sar (20 or 30 μM, 5 or 10 min, respectively) was measured at pH 6.0 with increasing concentrations of the test compounds (0–100 mM). Constants were derived from the competition curves shown in Figure 3. Parameters are shown ± S.E. (n = 4).

Compound	K_{i hPEPT1}	Rank at hPEPT1	K_{i hPEPT2}	Rank at hPEPT2	K_{i hPEPT1}/K_{i hPEPT2}
	mM		mM
Gly-Sar	0.44 ± 0.01		0.12 ± 0.02		3.6
Zofenopril	0.05 ± 0.01	1	0.024 ± 0.002	1	2.1
Quinapril	0.71 ± 0.03	2	0.09 ± 0.02	2	7.9
Benazepril	0.91 ± 0.05	3	0.18 ± 0.01	4	5.1
Spirapril	1.9 ± 0.2	4	0.17 ± 0.02	3	11
Quinaprilat	>3.16 (≈6)^†	5	1.6 ± 0.3	5	3.7
Enalapril	10 ± 1	6	3.6 ± 0.2	6	2.8
Captopril	43 ± 7	7	16 ± 1	7	2.7

↵† K_i value extrapolated beyond measurement range because of limited solubility of compound. See Figure 3 for maximal substrate concentrations used