Neonatal rat cardiac fibroblasts express three types of voltage-gated K⁺ channels: regulation of a transient outward current by protein kinase C

Abstract

Walsh KB, Zhang J. Neonatal rat cardiac fibroblasts express three types of voltage-gated K ϩ channels: regulation of a transient outward current by protein kinase C. Am J Physiol Heart Circ Physiol 294: H1010-H1017, 2008. First published December 21, 2007 doi:10.1152/ajpheart.01195.2007.-Cardiac fibroblasts regulate myocardial development via mechanical, chemical, and electrical interactions with associated cardiomyocytes. The goal of this study was to identify and characterize voltage-gated K ϩ (Kv) channels in neonatal rat ventricular fibroblasts. With the use of the whole cell arrangement of the patch-clamp technique, three types of voltagegated, outward K ϩ currents were measured in the cultured fibroblasts. The majority of cells expressed a transient outward K ϩ current (Ito) that activated at potentials positive to Ϫ40 mV and partially inactivated during depolarizing voltage steps. Ito was inhibited by the antiarrhythmic agent flecainide (100 M) and BaCl2 (1 mM) but was unaffected by 4-aminopyridine (4-AP; 0.5 and 1 mM). A smaller number of cells expressed one of two types of kinetically distinct, delayed-rectifier K ϩ currents [IK fast (IKf) and IK slow (IKs)] that were strongly blocked by 4-AP. Application of phorbol 12-myristate 13-acetate, to stimulate protein kinase C (PKC), inhibited Ito but had no effect on IKf and IKs. Immunoblot analysis revealed the presence of Kv1.4, Kv1.2, Kv1.5, and Kv2.1 ␣-subunits but not Kv4.2 or Kv1.6 ␣-subunits in the fibroblasts. Finally, pretreatment of the cells with 4-AP inhibited angiotensin II-induced intracellular Ca 2ϩ mobilization. Thus neonatal cardiac fibroblasts express at least three different Kv channels that may contribute to electrical/chemical signaling in these cells. cardiac fibroblasts DEVELOPMENT OF THE VERTEBRATE myocardium requires the interaction of several cell types, including myocytes, fibroblasts, smooth muscle cells, and endothelial cells (2, 3). Although cardiac myocytes make up the bulk of the myocardial volume, the cardiac fibroblast is the most numerous cell type found in the heart and functions in the deposition of the extracellular matrix (2, 3). In addition, fibroblasts can serve as "sentinel cells" that coordinate the myocardial response to chemical and mechanical stimulation through the release of cytokines and growth factors (2,3,15). Release of these signals during myocardial injury may regulate the extent of cardiac hypertrophy and fibrosis during the healing process (5, 15).Recent experiments suggest that cardiac fibroblasts also serve to relay electrical signals in the heart. When plated in primary culture, cardiac fibroblasts form physical interactions with cardiac myocytes through establishment of gap-junctional channels (6,8,14). With the use of a heterocellular culture model, it was established that fibroblasts are capable of relaying electrical excitation over distances as long as 300 m between strands of cardiac myocytes (14). However, the ionic mechanisms responsible for this electrical propagation are not well understoo...

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