Fig. 3. Bupivacaine-induced C/EBP homologous protein (CHOP) expression in human myotubes. (A ) Human myotubes were treated with vehicle alone (Ctl) or with the indicated concentrations of bupivacaine and 1 μm staurosporine (S) or 100 nm thapsigargin (T), a known inducer of CHOP expression and sarco/endoplasmic reticulum stress. After 18 h, myotubes were fixed and incubated with anti-CHOP antibody as indicated, followed by fluorescently labeled secondary antibodies. DNA was stained with 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI). (B ) The percentage of CHOP-positive nuclei was determined in fluorescent experiments. Values are the mean ± SEM (n = 4); P < 0.05 with one-way analysis of variance and *P < 0.05 with post hoc unpaired t test versus control (Ctl) with Holm's procedure; §P < 0.05 with unpaired t test versus control (Ctl). Scale bars = 10 μm.