Although Cl- channels have been the subject of investigations in the heart for nearly thirty years, it is only within the last five years that any consensus has emerged regarding the identification of such channels and their functional role in mammalian heart. The most extensively studied Cl- channel in heart is activated through the cAMP-protein kinase A pathway. Evidence suggests that under normal physiological conditions, activation of this channel plays a key role in autonomic regulation of resting membrane potential and the duration of the cardiac action potential. Cardiac Cl- channels, therefore, may represent new potentially important target sites for the development of class III antiarrhythmic agents. Other types of Cl- conductances which have recently been identified in mammalian heart include those activated by Ca2+i, protein kinase C, ATP, membrane stretch and anion channels activate under basal conditions. Little data is currently available on the molecular structure of any of these putative Cl- channels in heart. Very recent molecular studies from this laboratory, however, suggest that the cardiac cAMP-dependent Cl- channel is encoded by an alter-natively spliced isoform of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel which is found in various epithelial cells and believed to be defective in patients with cystic fibrosis. Included in this revised application is the full length sequence of the rabbit cardiac CFTR Cl- channel, which is shown to exhibit over 90% homology (excluding the alternatively spliced region) to the human epithelial CFTR gene product. This data presently represents the only molecular information currently available on the structure of any putative cardiac Cl- channel. This revised application requests support of electrophysiological and molecular biological studies aimed at characterizing the properties of Cl- channels in guinea-pig, rabbit and human heart.
The specific aims i nclude: isolation and expression of full length cDNAs which encode each type of cardiac Cl- channel, comparison of the biophysical properties of these channels in native cardiac myocytes and in heterologous expression systems, and finally an examination of the mechanism responsible for the previously observed Na+ sensitivity of the cardiac CFTR Cl- channel. These studies will specifically test the hypothesis that some of the recently described Cl- channels in native cardiac cells may be encoded by a family of genes related to CFTR. We will also examine whether or not these cardiac Cl- channels are structurally related to other types of recently cloned voltage-dependent Cl- channels. The proposed experiments should help fill the existing gap of current knowledge regarding the properties, physiological role and molecular structure of Cl- channels in the heart.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL052803-03
Application #
2668730
Study Section
Cardiovascular and Pulmonary Research A Study Section (CVA)
Project Start
1996-03-08
Project End
2001-02-28
Budget Start
1998-03-01
Budget End
1999-02-28
Support Year
3
Fiscal Year
1998
Total Cost
Indirect Cost
Name
University of Nevada Reno
Department
Physiology
Type
Schools of Medicine
DUNS #
146515460
City
Reno
State
NV
Country
United States
Zip Code
89557
Hume, J R; Duan, D; Collier, M L et al. (2000) Anion transport in heart. Physiol Rev 80:31-81
Nagasaki, M; Ye, L; Duan, D et al. (2000) Intracellular cyclic AMP inhibits native and recombinant volume-regulated chloride channels from mammalian heart. J Physiol 523 Pt 3:705-17
Duan, D; Ye, L; Britton, F et al. (2000) A novel anionic inward rectifier in native cardiac myocytes. Circ Res 86:E63-71
Britton, F C; Hatton, W J; Rossow, C F et al. (2000) Molecular distribution of volume-regulated chloride channels (ClC-2 and ClC-3) in cardiac tissues. Am J Physiol Heart Circ Physiol 279:H2225-33
Duan, D; Cowley, S; Horowitz, B et al. (1999) A serine residue in ClC-3 links phosphorylation-dephosphorylation to chloride channel regulation by cell volume. J Gen Physiol 113:57-70
Duan, D; Ye, L; Britton, F et al. (1999) Purinoceptor-coupled Cl- channels in mouse heart: a novel, alternative pathway for CFTR regulation. J Physiol 521 Pt 1:43-56
Yamazaki, J; Britton, F; Collier, M L et al. (1999) Regulation of recombinant cardiac cystic fibrosis transmembrane conductance regulator chloride channels by protein kinase C. Biophys J 76:1972-87
Horowitz, B; Ward, S M; Sanders, K M (1999) Cellular and molecular basis for electrical rhythmicity in gastrointestinal muscles. Annu Rev Physiol 61:19-43
Warth, J D; Hume, J R (1997) Re-examination of Na+-dependent regulation of cAMP-dependent Cl- currents in the heart. Pflugers Arch 433:597-607
Yamazaki, J; Hume, J R (1997) Inhibitory effects of glibenclamide on cystic fibrosis transmembrane regulator, swelling-activated, and Ca(2+)-activated Cl- channels in mammalian cardiac myocytes. Circ Res 81:101-9

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