Proteinase-activated receptor-2 (PAR-2) may participate in epithelial ion transport regulation. Here we examined the effect of mouse activating peptide (mAP), a specific activator of PAR-2, on electrogenic transport of mouse distal colon using short-circuit current (ISC) measurements. Under steady-state conditions, apical application of amiloride (100 μM) revealed a positive ISC component of 74.3 ± 6.8 μA cm-2 indicating the presence of Na+ absorption, while apical Ba2+ (10 mM) identified a negative ISC component of 26.2 ± 1.8 μA cm-2 consistent with K+ secretion. Baseline Cl- secretion was minimal. Basolateral addition of 20 μM mAP produced a biphasic ISC response with an initial transient peak increase of 11.2 ± 0.9 μA cm-2, followed by a sustained fall to a level 31.2 ± 2.6 μA cm-2 (n = 43) below resting ISC. The peak response was due to Cl- secretion as it was preserved in the presence of amiloride but was largely reduced in the presence of basolateral bumetanide (20 μM) or in the absence of extracellular Cl-. The secondary decline of ISC was also attenuated by bumetanide and by Ba2+ indicating that it is partly due to a stimulation of K+ secretion. In addition, the amiloride-sensitive ISC was slightly reduced by mAP, suggesting that inhibition of Na+ absorption also contributes to the ISC decline. Expression of PAR-2 in mouse distal colon was confirmed using RT-PCR and immunocytochemistry. We conclude that functional basolateral PAR-2 is present in mouse distal colon and that its activation stimulates Cl- and K+ secretion while inhibiting baseline Na+ absorption.
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