The Response of Chloride Transport to Cyclic AMP, Calcium and Hypotonic Shock in Normal and Cystic Fibrosis Fibroblasts
Cl- transport was shown to be altered in skin fibroblasts from cystic fibrosis (CF) patients (Rugolo et al.,1986), and an abnormal Cl- metabolism was also observed by Mattes et al. (1987). In the present study we have investigated the effect of two cAMP analogs, 8-Bromo cyclic AMP (8-Br-cAMP) and dibutyryl cyclic AMP (dbt-cAMP), of a beta agonist, isoproterenol, on 36C1- efflux from normal and CF fibroblasts. Cl- efflux consists of a superposition of two efflux events, operationally defined as two compartments, each exhibiting first order exponential decay. In table 1 it is shown that 15 min preincubation in the presence of cAMP analogs (O.lmM 8-Br-cAMP and ImM dbt-cAMP) and isoproterenol (5µM) increased the rate constant (k) of Cl-efflux from the fast compartment of 10%, 5% and 9% respectively, in both normal and CF fibroblasts. These results are in disagreement with those previously reported by Lin and Gruenstein, 1987, who observed a 13% stimulation of Cl- efflux in normal fibroblasts, but failed to detect any activation in CF cells. However, in our experiments, the extent of activation of Cl- transport by the cAMP-dependent effectors was weak in control cells, so that no difference could be detected between normal and CF fibroblasts.