Clearance of [14C] adenosine and [3H] mannitol across the 8d-old CPEC monolayers. (A) The donor was the upper chamber. (B) The donor was the lower chamber. Experiments were performed on CPEC monolayers from at least 2 animals. The concentration of [14C] adenosine was 125 nM, which represented about 5% of Km of [3H] adenosine uptake by the basolateral side of sheep CPEC in situ (I. Markovic, PhD Thesis, University of Belgrade, 1998). The clearance was linear; however, the values obtained were quite close to the values of [3H] mannitol clearance. Using these data points the permeability of CPEC monolayers for [14C] adenosine was calculated and these values are presented in Table 1.