The eccrine sweat gland is one of the target organs in cystic fibrosis (CF). The CF gene has been cloned and identified as cAMP-dependent Cl channel in other laboratories. The most common mutation is the loss of a phenylalanine at position 508 (deltaF508). deltaF508 comprises approximately 70% of CF patients. However, more than 300 different mutations have been reported to date. Despite the giant leap in knowledge regarding the genetic basis of CF and the biochemical and biophysical nature of the CFTR Cl channel, a number of questions remain. For example, the mutation at deltaF508 is associated with mislocalization of its gene product due to abnormal transport of proteins from the Golgi apparatus to the plasma membrane but those deltaF508 CFTR Cl channels, if properly localized in the plasma membrane, are partially functional, Thus hypofunction of Cl channels per se cannot fully account for the severe clinical manifestation of deltaF508. It is possible that deltaF508 is also associated with abnormal transport of other proteins or disruption of other unknown cellular functions. Interestingly, patients with nonsense mutations, who apparently lack CFTR, have a rather mild clinical phenotype. This observation suggests that cells can survive in the absence of CFTR Cl channels and that other Cl channels may substitute for CFTR when needed. Several Cl channels that could substitute for CFTR include: a Cl channel stimulated during cell volume increase, a Ca-stimulated Cl channel, an outwardly rectifying Cl channel (ORDIC), and a minoxidil sulfate-stimulated Cl channel recently observed in our laboratory. Thus it is important to understand regulation of all types of Cl channels. Understanding other unknown features of CF such as hyperactivity of Na channels, abnormal regulation of cellular pH and possible partial correction of the CF abnormality by methylxanthine is also crucial. Normal regulation of CFTR gene expression is also unknown. We propose to: 1. clarify the characterization and pharmacological regulation of Cl and other ionic channels and cytosolic pH in CF sweat secretory and duct cells using whole cell/patch clamp techniques, 2. study regulation of Na channels and their mRNA regulation in the CF duct, 3. examine pharmacological regulation of CFTR mRNA, 4. delineate characteristics of other Cl channels such as Ca-dependent, volume activated, minoxidil stimulable, or rectifying Cl channels that are also present in the sweat duct and 5. study gene regulation of P-glycoprotein, a putative membrane protein for volume activated Cl channels. Without Cl transport cells cannot survive nor can sweat secretion and ductal absorbtion take place. The sweat gland is an excellent tissue for CF research because it is easily accessible by minor biopsy and is free of secondary damage from such processes as infection. An increased understanding of Cl transport in the sweat gland not only compliments other CF research but also expands our knowledge of the sweat gland itself and its mechanism of function.
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