Figure 1.

Periarterial differentiation of Purkinje fibers in vivo and ET-dependent induction of the impulse-conducting cells in vitro. (a) Arrangement of the avian cardiac conduction system consisting of the proximal (blue) and distal (green) subcomponents. Immunolabeling of Cx42 (b and c) and sMHC (e and f) (green signals) in conducting cells, cMyBP-C (b–e, red signals) in contractile myocytes, sarcomeric myosins (d, green signals) in both cell types, and smooth muscle α-actin (f, red signal) in coronary arterial bed of the ventricular myocardium. Conversion of isolated E3 myocytes from cMyBP-C positive (red signal) to sMHC-positive (green signal) after exposure to ET (10⁻⁷M) for 1 day (g), 3 days (h), and 5 days (i). SAN, the sinuatrial node; AVN, the atrioventricular node; B, the atrioventricular bundle and bundle branches; P, the Purkinje fiber network. Asterisks indicate the lumen of arteries.