REGULATION OF CHLORIDE ION CONDUCTANCE IN PANCREAS DUCT

Case Western Reserve University, Cleveland OH

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Abstract

Cystic Fibrosis (CE) is a multi-system disease caused by mutations in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) protein. Normally the protein functions as a cAMP-regulated C1-channel in the apical plasma membrane. The precise link between defective CFTR and the pathophysiology of CF is not known. It is generally assumed that CF results from abnormal ion and water movement across affected epithelia; however, other regulatory functions ascribed to CFTR may contribute to the disease. Genetic and pharmacologic restoration of apical membrane C1-permeability in CF epithelia are often cited as a viable therapeutic strategies. One such approach is to activate "alternate" apical membrane, non-CFTR C1-channels. The rationale for this approach rests upon the observation that Ca2+-activated C1-conductance (CACC) is preserved in human CF airway epithelia and that organ-specific disease severity in the CF knockout mouse is inversely related to the activity of CACC. Pancreatic duct epithelial cells express at least 4 types of plasma membrane C1-conductances: cAMP-activated (CFTR), cAMP-activated (non-CFTR), CACC, and swelling activated (SACC). At least two, and perhaps as many as four, different plasma membrane anion channels underlie these four conductance pathways. The molecular identity of only one (CFTR) is known. Regulation of the CACC, cAMP-activated (non-CFTR), and SACC conductances has received little attention in pancreatic duct cells. Our previous studies revealed that the Ca2+-activated and the cAMP-activated (non-CFTR) conductances are present in the apical cell membrane of pancreatic duct cells and thereby represent potential pathways to circumvent the loss of functional CFTR. The goal of the work described in this proposal is to identify the single channel basis for these two conductances and to determine the regulatory pathways that control channel activity. Electrophysiological measurements of channel function in response to manipulation of signal transduction pathways will be used. The long term objective of the work is to develop pharmacologic approaches to control salt and water transport so as to compensate for loss of CFTR function in epithelia affected by cystic fibrosis.