Intestinal conductance and permsdectivity changes with theophylline and choleragen

POWELL, D. W. Intestinal conductance and permselectiuity changes z.&h thcophylline and choleragen. Am. J. Physiol. 227(6) : 1436-1443. 1974.-Theophylline and choleragen reduced the electrical conductance of the in vitro rabbit ileum SOc/, and 25yi, respectively, increased the potential difference and caused only a relatively short-lived increase in short-circuit current. The increase in shortcircuit current with theophylline was a function of bathing solution [Na] at fixed anion concentrations and a function of [Cl] at fixed Na concentrations. The conductance change was also dependent on the presence of Na plus either Cl or HC03, both anions being necessary for a maximal. effect, Since passive ion movement through the transepithelial shunt path largely determines the total conductance of low-resistance epithelia, these results suggest that theophylline and choleragen, presumably via increased cellular cyclic ,4MP (CAMP), reduce the magnitude of the shunt. The relative permeabilities (p) of K, Na, and Cl were determined in ouabain-treated ileum by measuring dilution and bi-ionic potentials created by the replacement of mucosal solution NaCl with mannito1 or KCl. In control ileum the PK :PNa :pCl was 1.. 17-l. 18 : 1 .OO : 0.40-0.47. Theophylline and choleragen had no significant effect on the pK:pSs. However, theophylline significantly increased the pcl :p,, from 0.47 to 0.68, and choleragen increased the pc@Na from 0.40 to 0.57 (43-45yG). The site of this permselectivity alteration cannot be determined with certainty, but the evidence favors the transepithelial shunt path as the location. Thus, in addition to changing the magnitude of the shunt, increased epithelial cA?r/lP levels may alter the permselectivity characteristics of this pathway.