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Table 1.

Inhibition of fluorescein accumulation (at 0.5 μmol l–1) by compounds known to inhibit organic solute transport in other systems

Uptake rate
CompoundConcentration (mmol l-1)ControlaTreatmentbN
p-Aminohippuric acid 93.6±4.7 75.8±16.3 
Probenecid 0.1 96.9±3.6 92.5±8.1 
Probenecid 90.7±3.7 -19.1±11.0* 
Bromosulfophthalein 0.1 – 12.8±8.4 
Methotrexate 0.5 89.7±2.6 10.8±8.6* 
Verapamil 0.1 95.8±4.5 52.6±12.3* 
Verapamil 94.6±5.3 -15.7±8.8* 
Tetraethylammonium 98.2±3.5 95.4±6.8 
Salicylic Acid 96.0±4.1 57.4±4.8* 
Penicillin 91.3±2.7 63.8±5.3* 
Uptake rate
CompoundConcentration (mmol l-1)ControlaTreatmentbN
p-Aminohippuric acid 93.6±4.7 75.8±16.3 
Probenecid 0.1 96.9±3.6 92.5±8.1 
Probenecid 90.7±3.7 -19.1±11.0* 
Bromosulfophthalein 0.1 – 12.8±8.4 
Methotrexate 0.5 89.7±2.6 10.8±8.6* 
Verapamil 0.1 95.8±4.5 52.6±12.3* 
Verapamil 94.6±5.3 -15.7±8.8* 
Tetraethylammonium 98.2±3.5 95.4±6.8 
Salicylic Acid 96.0±4.1 57.4±4.8* 
Penicillin 91.3±2.7 63.8±5.3* 

All values are means ± s.e.m.; N = number of tubules per sample. Negative values represent trials in which the introduction of test compound resulted in a net FL efflux from the tubule (a decrease in fluorescence).

–, Missing control trials

a

Control uptake rate (in absence of inhibitor) is the rate during the second measurement period (no inhibitor) expressed as percent of uptake measured in the first measurement period. See text for details

b

Treatment uptake rate (in presence of inhibitor) during second measurement period (inhibitor present) expressed as percent of uptake measured in the first measurement period

*

Change in uptake rate in presence of inhibitor significantly different from change in uptake rate in absence of inhibitor; P<0.05, paired t-test

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