Fig. 1.
Ussing chamber tracings showing a chloride secretory response when a sterile filtrate of cecal contents from rabbits infected with rabbit EPEC strain RDEC-1 was applied to uninfected T84 cell monolayers. T84 cells were grown on Snap-Well inserts as described in Materials and Methods and chloride secretion is measured as short-circuit current (Isc). Both panels show responses to pooled cecal filtrates from two rabbits; test fluids were added to the apical side of the monolayer. Panel A, a sterile filtrate of cecal fluids from uninfected control rabbits produced only a small secretory response and the response was not affected by 8-sulfophenyltheophylline (8-SPT), an adenosine receptor antagonist. Panel B, 0.8 ml of a sterile filtrate from cecal contents of rabbits infected for 7 days with RDEC-1 triggered a large and brisk short-circuit current in the T84 cell monolayer and the response was abolished by MRS1754, an adenosine antagonist selective for adenosine A2b receptors. The total volume of buffer in the apical chamber in these experiments was 6.5 ml. Panel C, Isc response to 1 μM adenosine and reversal by MRS1754. Panel D, standard curve of Isc vs. adenosine in the Ussing chamber. The solid curve indicates the best-fit to the data, while the dotted lines indicate upper and lower 95% confidence limits.