Basolateral PAR-2 receptors mediate KCl secretion and inhibition of Na+ absorption in the mouse distal colon

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 (I-SC) measurements. Under steady-state conditions, apical application of amiloride (100 muM) revealed a positive I-SC component of 74.3 +/- 6.8 muA cm(-2) indicating the presence of Na+ absorption, while apical Ba2+ (10 mm) identified a negative I-SC component of 26.2 +/- 1.8 muA cm(-2) consistent with K+ secretion. Baseline Cl- secretion was minimal. Basolateral addition of 20 muM mAP produced a biphasic I-SC response with an initial transient peak increase of 11.2 +/- 0.9 muA cm(-2), followed by a sustained fall to a level 31.2 +/- 2.6 muA cm(-2) (n = 43) below resting I-SC. 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 muM) or in the absence of extracellular Cl-. The secondary decline of I-SC 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 I-SC was slightly reduced by mAP, suggesting that inhibition of Na+ absorption also contributes to the I-SC 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.