Role of apical H-K exchange and basolateral K channel in the regulation ofintracellular pH in rat distal colon crypt cells

An apical membrane ouabain-sensitive H-K exchange and a barium-sensitive ba solateral membrane potassium channel are present in colonic crypt cells and may play a role in both K absorption and intracellular pH (pH(i)) regulati on. To examine the possible interrelationship between apical membrane H-K e xchange and basolateral membrane K movement in rat distal colon in the regu lation of pH(i), experiments were designed to assess whether changes in ext racellular potassium can alter pH(i). pH(i) in isolated rat crypts was dete rmined using microspectrofluorimetric measurements of the pH-sensitive dye BCECF-AM (2',7'-bis(carboxyethyl-5(6)-carboxy- fluorescein acetoxy methyles ter). After loading with the dye, crypts were superfused with a Na-free sol ution which resulted in a rapid and reversible fall in pH(i) (7.36 +/- 0.02 to 6.98 +/- 0.03). Following an increase in extracellular [K] to 20 mM, in the continued absence of Na, there was a further decrease in pH(i) (0.20 /- 0.02, P < 0.01). K-induced acidification was blocked both by 2 mM bath b arium, a K channel blocker, and by 0.5 mM lumen ouabain. K-induced acidific ation was also observed when intracellular acidification was induced by a N H4Cl prepulse. These observations suggest that increased basolateral K move ment increases intracellular [K] resulting in a decrease in pH(i) that is m ediated by a ouabain-sensitive apical membrane H,K-ATPase. Our results demo nstrate an interrelationship between basolateral K movement and apical H-K exchange in the regulation of pH(i) and apical K entry in rat distal colon.