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 μM) revealed a positive I_SC component of 74.3 ± 6.8 μA cm^-2 indicating the presence of Na⁺ absorption, while apical Ba²⁺ (10 mM) identified a negative I_SC 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 I_SC 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 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 μM) 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.