CYCLIC AMP-RELATED AND CATION-AFFECTED HUMAN PLATELET CHLORIDE TRANSPORT REGULATION

Cystic fibrosis has been characterized as a defect in the regulation o f cyclic AMP-dependent transepithelial chloride transport, The activat ion of cyclic AMP-dependent protein kinase A by cyclic AMP occurs norm ally in cystic fibrosis cells, but they fail to transport chloride ion s in response to protein kinase A stimulation. Defective chloride secr etion and abnormal electrolyte transport occurs in several organs incl uding the lung, sweat glands, intestine and pancreas. The present work was aimed at exploring whether the same or similar regulatory systems are functional in platelets, and if they are altered or deficient in individuals with cystic fibrosis. Chloride transport in platelets from normal subjects and from cystic fibrosis patients was measured by cel l sizing techniques where chloride permeability is the limiting factor . In platelets from healthy volunteers, the chloride channel blocker, 5-nitro-2-(3-phenylpropylamino) benzoic acid, inhibits the transport i n a dose-dependent manner. The preservation of chloride transport capa bility is shown to be dependent upon the presence of either Ca2+ or tw o divalent cation substitutes, Cd2+ or Cu2+. It is also shown that in normal subjects 0.1 mu mol/l prostaglandin E(1), which elevates cyclic AMP 6 times and abolishes platelet aggregation, significantly enhance s the rate constant of the transport. Furthermore, in five out of nine cystic fibrosis patients studied, platelet chloride transport did not respond to stimulation by prostaglandin E(1).