FIG. 6.

Hearts from mutant transgenic mice might have suffered from ER stress. (A) Neonatal myocytes from a mutant KDEL receptor transgenic (TG) mouse and its littermate C57BL/6 mouse were cultured. Forty-eight hours later, the cells were fixed with or without treatment with tunicamycin (Tm, 3 μg ml⁻¹) at 37°C for 12 h. The myocytes were evaluated by fluorescence microscopy with a mouse anti-BiP monoclonal antibody. Bar, 10 μm. (B) Accumulation of ubiquitinated proteins in the hearts of mutant KDEL receptor transgenic mice. Western blotting of heart lysates with an anti-ubiquitin antiserum (Ub) and an antitroponin T antiserum. Lane 1, wild-type KDEL receptor transgenic mouse (56 weeks old); lane 2, C57BL/6 mouse (34 weeks old); lane 3, mutant KDEL receptor transgenic mouse (line F, 34 weeks old). Both transgenic mice were Cre gene positive. (C) Expression of BiP, CHOP, troponin T, and Myc-tagged KDEL receptors in hearts from wild-type, mutant KDEL receptor transgenic (lines B and F), and C57BL/6 mice (8 weeks old) was evaluated by Western blotting. All the mice were Cre gene negative.