Abstract 15935: Growth Factors Increase Gap Junctional Coupling in Hybrid Cardiomyocyte-Myofibroblast Cell Pairs
INTRODUCTION. Previous in-vitro studies demonstrated that cardiac myofibroblasts (MFBs) induce arrhythmogenic slow conduction and ectopic activity following establishment of gap junctional coupling to cardiomyocytes (CMCs). Because differentiation and proliferation of MFBs is primarily controlled by transforming growth factor-β1 (TGF-β1) and platelet derived growth factor (PDGF), we tested the hypothesis that these growth factors may promote MFB arrhythmogeneicity by increasing gap junctional coupling to CMCs.
METHODS. Experiments were performed with primary co-cultures of neonatal rat ventricular CMCs and MFBs. Intercellular gap junctional conductance (gj) in homo- and heterocellular cell pairs was recorded using standard dual whole cell patch clamp protocols.
RESULTS. Intercellular conductances of homo- and heterocellular cell pairs were linearly dependent on the lengths of cell-cell contacts (CL) that ranged from 4 µm to 95 µm (R2 > 0.8). Based on linear regression analysis of the data (n ≥ 7 for each experimental condition), gj for an average CL of 50 µm was 351 nS for CMC-CMC cell pairs and 74 nS for MFB-CMC cell pairs. Exposing the preparations to TGF-β1 (2.5 ng/ml; 24-48 hrs) had no significant effect on gj of CMC-CMC cell pairs (365 nS) but caused a substantial increase of gj in MFB-CMC preparations to 121 nS (+ 64%). A similar effect was observed when exposing MFB-CMC cell pairs to PDGF (50 ng/ml; 24 to 48 hrs) which caused gj to increase to 122 nS. Vice versa, blocking of the TGF-β1 receptor with SB-431542 (10 µmol/L; 24-48 hrs; no exogenous TGF-β1 present) reduced gj of MFB-CMC cell pairs to 33 nS while having no effect on CMC-CMC cell pairs (352 nS). When assuming that gj of MFB-CMC cell pairs in presence of SB431542 reflects baseline coupling, TGF-β1 caused an overall increase of gj by 265%. Western blot analysis of Cx43 expression showed an increase (TGF-β1) and a decrease (SB431542), respectively, which suggests that TGF-β1 regulates gj by modulation of Cx43 protein synthesis.
CONCLUSIONS. These findings demonstrate that the fibrogenic growth factors TGF-β1 and PDGF cause a substantial upregulation of gap junctional coupling in heterocellular MFB-CMC cell pairs which may aggravate the arrhythmogenic influence of MFBs on CMCs.
- © 2012 by American Heart Association, Inc.