Table 3.

Effect of selected thiazole derivatives on vanadate-sensitive ATPase activity of P-glycoprotein

Compd	ATPase activity (nmoles Pi/min/mg protein)[a]	Fold stimulation
13	78	2.80
14	41.40	1.47
15	60.70	2.16
17	78.75	2.81
18	83.70	2.98
19	54.30	1.93
20	42.15	1.50
21	77.20	2.75
22	89.4	3.31
23	92.3	3.42

^[a]Crude membranes (100 μg protein/ml) from P-gp expressing High-Five cells were incubated at 37 °C with 2.5 μM of selected derivatives in the presence and absence of 0. 3 mM sodium orthovanadate in ATPase assay buffer for 5 min, and the vanadate-sensitive ATPase activity of P-gp was determined as described.^[44] The vanadate-sensitive ATPase activity was calculated as nmoles P_i/min/mg protein and expressed as fold stimulation with respect to basal ATPase activity (in the presence of solvent DMSO) taken as 1.0. With the same membranes 50 μM verapamil stimulated the ATPase activity of P-gp by 2.5-fold (70 nmoles P_i/min/mg protein).The values are an average of two independent experiments.