title: Na(+) current expression in human atrial myofibroblasts: identity and functional roles.
abstract: In the mammalian heart fibroblasts have important functional roles in both healthy conditions and diseased states. During pathophysiological challenges, a closely related myofibroblast cell population emerges, and can have distinct, significant roles. Recently, it has been reported that human atrial myofibroblasts can express a Na(+) current, INa. Some of the biophysical properties and molecular features suggest that this INa is due to expression of Nav 1.5, the same Na(+) channel α subunit that generates the predominant INa in myocytes from adult mammalian heart. In principle, expression of Nav 1.5 could give rise to regenerative action potentials in the fibroblasts/myofibroblasts. This would suggest an active as opposed to passive role for fibroblasts/myofibroblasts in both the "trigger" and the "substrate" components of cardiac rhythm disturbances. Our goals in this preliminary study were: (i) to confirm and extend the electrophysiological characterization of INa in a human atrial fibroblast/myofibroblast cell population maintained in conventional 2-D tissue culture; (ii) to identify key molecular properties of the α and β subunits of these Na(+) channel(s); (iii) to define the biophysical and pharmacological properties of this INa; (iv) to integrate the available multi-disciplinary data, and attempt to illustrate its functional consequences, using a mathematical model in which the human atrial myocyte is coupled via connexins to fixed numbers of fibroblasts/myofibroblasts in a syncytial arrangement. Our experimental findings confirm that a significant fraction (approximately 40-50%) of these human atrial myofibroblasts can express INa. However, our data suggest that INa may be generated by a combination of Nav 1.9, Nav 1.2, and Nav 1.5. Our results, when complemented with mathematical modeling, provide a background for re-evaluating pharmacological management of supraventricular rhythm disorders, e.g., persistent atrial fibrillation.
authors.affiliation: Simula Research Laboratory, Center for Biomedical Computing and Center for Cardiological Innovation Oslo, Norway.
authors.forename: Jussi T
authors.initials: JT
authors.lastname: Koivumäki
authors.affiliation: Faculty of Kinesiology, University of Calgary Calgary, AB, Canada.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Clark
authors.affiliation: Faculty of Kinesiology, University of Calgary Calgary, AB, Canada.
authors.forename: Darrell
authors.initials: D
authors.lastname: Belke
authors.affiliation: Faculty of Kinesiology, University of Calgary Calgary, AB, Canada.
authors.forename: Colleen
authors.initials: C
authors.lastname: Kondo
authors.affiliation: Division of Cardiothoracic Surgery, Department of Cardiac Sciences, University of Calgary Calgary, AB, Canada.
authors.forename: Paul W M
authors.initials: PW
authors.lastname: Fedak
authors.affiliation: Simula Research Laboratory, Center for Biomedical Computing and Center for Cardiological Innovation Oslo, Norway.
authors.forename: Mary M C
authors.initials: MM
authors.lastname: Maleckar
authors.affiliation: Faculty of Kinesiology, University of Calgary Calgary, AB, Canada.
authors.forename: Wayne R
authors.initials: WR
authors.lastname: Giles
keywords: Na+ current; atrial arrhythmias; fibroblast; mathematical models; myofibroblast