Cardiac cushions modulate action potential phenotype during heart development [corrected].

The extracellular matrix plays an important role in cardiac function. Its role in the generation and modulation of electrical activity in the early stages of heart development has not been studied extensively. Our study demonstrates that the extracellular matrix in cardiac cushions can alter the action potential phenotype by direct contact with cardiomyocytes from different regions of the heart. We also demonstrate that fibronectin, an important and abundant component of the cardiac extracellular matrix, partially mimics the effects of the cushion tissue in altering the changes in action potential. Fibronectin increases I(Ca) (2+) and acutely increases cytosolic calcium. These findings suggest that the composition of the cardiac extracellular matrix during development plays an important role in defining patterns of electrical activity in the developing heart. (c) 2009 Wiley-Liss, Inc.