Microelectrode measurements of the effects of basolateral adenosine in polarized human intestinal epithelial cells in culture.

Activation of the basolateral receptor for adenosine in HT-29cl.19A cells, by 100 microM adenosine, increased the equivalent short-circuit current (DeltaIsc= 24+/-2 microA/cm2), depolarized the intracellular potential (DeltaVa= 26+/-2 mV) and decreased the fractional apical membrane resistance (DeltafRa=-0.48). The changes in all parameters reached their peak values simultaneously. This suggests that the primary action of the adenosine-activated pathway is on only one membrane. Bumetanide inhibited the transepithelial response and repolarized the cell potential. After preincubation with 100 microM forskolin, application of 300 microM adenosine caused a significant further change in Va, Isc, the transepithelial potential (Vt) and fRa. Together with the results from ion-replacement studies, the observations indicate that adenosine activates channels other than the cystic fibrosis transmembrane conductance regulator (CFTR). The rank order of potencies of adenosine and adenosine analogues implies that the receptor is of the A2 subtype. Preincubation with 4-bromophenacyl bromide (4-BPB) inhibited the effect of an adenosine analogue by 50%, indicating that activation of phospholipase A2 may be involved in the adenosine-induced response.