A, SUR2 and Kir6.1 protein expression in fibroblast cultures. Western blots were performed with whole cell lysates of cultured mouse ventricular fibroblasts at 5, 7 and 9 days after isolation. GAPDH was used as a loading control. B, Pinacidil-induced and glibenclamide-sensitive average current density in fibroblasts evaluated at 5, 7 and 9 days of culture. Current amplitude was measured as the average value obtained during a 10 s pulse at 50 mV from a holding potential of −50 mV in the whole cell configuration. Current amplitude was normalized to cell capacitance. Probability values correspond to comparisons to 5 days in culture. C, Fibronectin (green) and α-SMA (red) expression in cultured fibroblasts at different times in culture. Bar is 50 µm. (Modified with permission from Benamer N, Moha Ou Maati H, Demolombe S, Cantereau A, Delwail A, Bois P, Bescond J, Faivre JF. Molecular and functional characterization of a new potassium conductance in mouse ventricular fibroblasts. J Mol Cell Cardiol. 2009;46(4):508–517.)

Fibroblast transformation to the myofibroblast phenotype is associated with important changes in the biological behavior of these cells. Limited information is available regarding the electrophysiological consequences of this transition.

A, Representative immunoblot and quantification of relative Cx43 levels in cultured fibroblasts isolated from normal (Fb) and infarcted (MI-Fb) hearts. Protein expression levels were normalized to Fb. GAPDH was used as a loading control. B, Average permeability constants (k) obtained with gap-FRAP from myocytes plated on top of Fb and MI-Fb monolayers under control conditions and in the presence of 200 µM carbenoxolone (CBX). C–E, Representative activation maps from heterocellular cultures of myocytes and Fb plated on top. Fb were plated at 200, 400, and 600 cells/mm², respectively. Lines are 10 ms isochrones. F–H, Representative activation maps from heterocellular cultures of myocytes and MI-Fb plated at the same densities as panels C–E. I, Average CV of the heterocellular cultures for different fibroblast plating densities. Dotted line corresponds to average CV of homocellular myocyte monolayers (Myo). Closed and open symbols correspond to heterocellular cultures with Fb and MI-Fb, respectively. Probability values correspond to significant differences between Fb and MI-Fb at the same density. J, Average APD₇₀ of heterocellular cultures for different fibroblast plating densities. Dotted line corresponds to average APD₇₀ of Myo. Probability value corresponds to significant difference between Fb and MI-Fb at the same density. (Modified with permission from Vasquez C, Mohandas P, Louie KL, Benamer N, Bapat AC, Morley GE. Enhanced Fibroblast-Myocyte Interactions in Response to Cardiac Injury. Circ Res. 2010; 107(8):1011–1020.)