Thus there appear to be significant species differences in colonic apical BK channel expression, since apical BK channels are present mainly in the surface cells of rabbit distal colon (12), and immunostaining demonstrated increased expression of apical BK channels in surface colonocytes and upper crypt cells in patients with end-stage renal disease who exhibited increased distal colonic K+ secretion (25). This evidence concerns the gene KCNMA1 and stage 5 chronic kidney disease.