Submitted on October 15, 2007
Accepted on December 12, 2007
Neonatal Rat Cardiac Fibroblasts Express Three Types of Voltage-gated K+ Channels: Regulation of a Transient Outward Curent by Protein Kinase C
Kenneth B. Walsh1* and Jining Zhang2
1 Pharmacology and Physiology, University of South Carolina, Columbia, South Carolina, United States
2 Pharmacology, Physiology & Neuroscience, University of South Carolina, Columbia, South Carolina, United States
* To whom correspondence should be addressed. E-mail: walsh{at}med.sc.edu.
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+ (Kv) channels in neonatal rat ventricular fibroblasts. With the use of the whole-cell arrangement of the patch-clamp technique, three types of voltage-gated, outward K+ currents were measured in the cultured fibroblasts. The majority of cells expressed a transient outward K+ current (Ito) that activated at potentials positive to -40 mV and partially inactivated during depolarizing voltage steps. Ito was inhibited by the anti-arrhythmic agent flecainide (100 µM) and BaCl2 (1 mM), but was unaffected by 4-aminopryridine (4-AP) (0.5 &1 mM). A smaller number of cells expressed one of two types of kinetically distinct, delayed rectifier K+ 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, while having no effect on IKf and IKs. Immunoblot analysis revealed the presence of Kv1.4, Kv1.2, Kv1.5 and Kv2.1 α subunits, but not Kv4.2 nor Kv1.6 α subunits, in the fibroblasts. Finally, pretreatment of the cells with 4-AP inhibited angiotensin II-induced intracellular Ca2+ mobilization. Thus, neonatal cardiac fibroblasts express at least three different voltage-gated K+ channels that may contribute to electrical/chemical signaling in these cells.
