Fig. 6. Functional analyses of cardiac Na,K-ATPase isoforms. (A-E) Lateral views of 50 hpf embryos, head to the top. Ouabain treatment (C) and 1B1MO injection (D) create embryos morphologically indistinguishable from had mutants (B). The gross morphology of 2MO-injected embryos (E) is similar to that of wild-type controls (A). (F-O) Cardiac tissues are visualized by in situ hybridization using a vmhc probe. (F-J) Dorsal views of embryos at 24 hpf, head to the bottom; the arrows point to the heart. (K-O) Ventral views of 50 hpf embryos, head to the top; the solid line marks the constriction between the atrium (a) and the ventricle (v). (F) Wild-type control embryos at 24 hpf. Ouabain treatment (H) and 1B1MO (I) injection perturbed primitive heart tube extension in oneday-old embryos similar to the had mutation (G). (K) vmhc expression is restricted to the ventricle of wild-type control embryos at 50 hpf. The expression of vmhc extends into the atrium of had (L), ouabain-treated (M) and 1B1MO-injected (N) embryos. (J) Cardiac jogging is affected by 2MO. Some 2MO-injected embryos have the primitive heart tube placed on the right side of the embryos. After two days of development, abnormal cardiac looping is observed in 2MO-injected embryos. Some fail to loop and some have the ventricles on the left of the atrium (O).