Fig. 7. Ectopic induction of Purkinje fiber marker by the expression of exogenous ET_A. CXIZ- (A-F) or CXIZ-ETA- (G-L) infected heart tubes were removed from embryos, and ventricular segments were isolated and cultured in the absence (A-C,G-I) or the presence (D-F,J-L) of 10^–7 M of active ET-1 peptide. Tissues were double immunolabeled in whole mount with anti-ß-gal antibody (red signal) and ALD58 (green signal). Immunolabeled ventricular segments (A,D,G,J) were further processed for frozen sectioning (B,C,E,F,H,I,K,L). (B,E,H,K) ß-gal and (C,F,I,L) ALD58 signals in the same cultures. Arrows indicate cells positive for conduction cell marker ALD58. (M) Ratio of ALD58-positive cells per viral infected cells. In each experimental group, a total of 50-100 cells from five infected hearts were examined and averaged.