Fig. 5.

Effect of 5′-nucleotidase inhibitors on the chloride secretory response to AMP in T84 cells in the Ussing chamber. Short-circuit current (I_sc) was measured in T84 cells grown in Snapwell inserts as described in “Materials and methods”; in this cell line and electrode configuration, a positive I_sc (upward deflection on the graphs) represents chloride secretion in the basolateral to apical direction. All of the additions of agonists and inhibitors in these parts of the figure was on the apical (mucosal) side of the monolayers only. a Reversal of AMP-induced secretory response by theophylline, an adenosine receptor antagonist. b Partial inhibition of AMP-induced secretion by 2 mM zinc acetate, with restoration of the tracing to its previous trend by adenosine, demonstrating that adenosine receptors are not blocked by zinc. c Substantial reversal of I_sc by α,β-methylene-ADP when a low concentration of AMP (1 μM) is used as the stimulus. Note that adenosine fully restores secretion to its previous level. d Lesser degree of reversal of I_sc by α,β-methylene-ADP when a higher concentration of AMP (20 μM) is used as stimulus. e Summary of many experiments in which fixed concentrations of zinc and α,β-methylene-ADP were tested for inhibitory efficacy against varying concentrations of AMP as test stimulus. In Fig. 5e the slope of the α,β-methylene-ADP curve was −1.73 ± 0.5 by linear regression (95% confidence limits of the slope value −3.27 to −0.2, significantly different from zero, p < 0.04). In contrast the slope of the zinc curve was −0.04 ± 0.23 and did not differ significantly from zero