Table 2

Inhibitory effects of several endogenous compounds and xenobiotics on carnitine uptake by OCTN2-expressing HEK 293 cells

Inhibitor	Concentration	Relative Uptake
	μM	% of Control
Control		100
Endogenous Compounds
l-Carnitine	5	83.1 ± 1.14^2-150
Guanidine	500	91.3 ± 4.49
N ¹-methylnicoti namide	500	99.3 ± 2.94
Choline	500	74.6 ± 4.59^2-150
Acetylcholine	500	79.1 ± 1.22^2-150
Acetylcholine	5000	34.2 ± 0.33^2-150
Serotonin	500	81.4 ± 4.79
Serotonin	5000	51.3 ± 0.46^2-150
Dopamine	500	81.3 ± 0.85^2-150
Dopamine	5000	70.9 ± 0.46^2-150
Epinephrine	500	105.9 ± 2.11
Epinephrine	5000	106.1 ± 2.65
Norepinephrine	500	93.9 ± 5.77
Norepinephrine	5000	70.9 ± 0.46^2-150
Histamine	5000	100.0 ± 3.26
Thiamine	500	77.4 ± 2.25^2-150
Thiamine	5000	65.9 ± 0.58^2-150
α-Ketoglutarate	500	96.4 ± 1.58
PAH	500	100.4 ± 1.23
Xenobiotics
TEA	50	67.8 ± 0.37^2-150
TEA	500	15.4 ± 0.73^2-150
MPP	500	72.9 ± 1.79^2-150
Acetyl-ß-methylcho line	500	82.5 ± 1.54^2-150
Pyrilamine	500	36.3 ± 0.63^2-150
Diphenhydramine	500	43.6 ± 1.74^2-150
Procainamide	500	81.3 ± 1.87^2-150
Lidocaine	500	57.1 ± 1.14^2-150
Quinidine	500	6.1 ± 0.40^2-150
Verapamil	500	1.3 ± 0.12^2-150

The uptake of [³H]carnitine was measured for 3 min at 37°C in Na⁺-containing transport buffer, pH 7.4, containing each compound. Each value represents the mean ± S.E.M. of three determinations. The data represent the difference in uptakes by Mock and OCTN2-expressing HEK293 cells.

↵2-150 Significantly different from the control uptake by Student's t test (p < 0.05).