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5Laboratory of Cardiological Sciences, Gerontology Research Center, Division of 1Renal Medicine, Johns Hopkins Bayview Medical Center, and 4Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland 21224; and 2Center for Nephrology and 3Department of Physiology/Autonomic Neuroscience Institute, Royal Free and University College Medical School, University College London, London, W1T 3AA United Kingdom
Submitted 1 May 2003 ; accepted in final form 28 July 2003
The precise steps leading from mutation of the polycystic kidney disease (PKD1) gene to the autosomal dominant polycystic kidney disease (ADPKD) phenotype remain to be established. Fluid accumulation is a requirement for cyst expansion in ADPKD, suggesting that abnormal fluid secretion into the cyst lumen might play a role in disease. In this study, we sought to establish a link between polycystin-1 (the PKD1 gene product) and ATP-stimulated Cl secretion in renal tubule cells. To do this, we performed a whole cell patch-clamp analysis of the effects of expression of the isolated cytoplasmic COOH-terminus of polycystin-1 in stably transfected mouse cortical collecting duct cells. The truncated polycystin-1 fusion protein prolonged the duration of ATP-stimulated Cl conductance and intracellular Ca2+ responses. Both effects were dependent on extracellular Ca2+. It was determined that expression of the truncated polycystin-1 fusion protein introduced, or activated, an ATP-induced Ca2+ entry pathway that was undetectable in transfection control cell lines. Our findings are concordant with increasing evidence for a role of polycystin-1 in cell Ca2+ homeostasis and indicate that dysregulated Ca2+ entry might promote Cl secretion and cyst expansion in ADPKD.
autosomal dominant polycystic kidney disease; purinergic P2 receptors; chloride channels; kidney collecting tubules; patch-clamp techniques
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