Fig. 9. Ca_i²⁺ levels and heart laterality after treatment with proton ATPase antagonists. (A-C) Fura-2-loaded HH6 embryos were treated with the indicated agents and imaged ventrally. The upper panel shows a representative Fura-2 image; the lower panel is the line-scan quantitation of fluorescent intensity versus left-right axis for that embryo, at the position indicated by the yellow line in the upper panel. Hensen's node is indicated by an asterisk. (A) Untreated embryo. (B) The H⁺V-ATPase antagonist concanamycin reduces LR Ca_i²⁺. (C) The H⁺K⁺-ATPase antagonist lansoprazole elevates right Ca_i²⁺. (D) Embryos were treated with the indicated proton ATPase antagonists at HH4-HH6 and heart laterality was scored 20 hours later. The percentage of embryos with a right-looped (R, situs solitus) or left-looped (L, situs inversus) heart is shown; the number of embryos per treatment is indicated in parentheses. Treatments were: DMSO, concanamycin (100 µM) and lansoprazole (7 mM). Asterisk indicates situs inversus frequencies that significantly differ from controls by ² analysis (P<0.05).