Role of exosomal Cx43 in exosome uptake by glioma cells. (A) Expression level of Cx43 in sExo and rExo. GAPDH was used as endogenous reference. (B) Expression of Cx43 in U251s cells after treatment with PBS, sExo and rExo for 48 h. GAPDH was used as endogenous reference. (C and D) The relative expression level of Cx43 was indicated as the ratio of Cx43/GAPDH in each group. Data represent the results of at least three independent experiments for each condition. **P<0.01, ***P<0.001. (E) Exosome uptake in U251s cells after treatment with Dio-sExo, Dio-rExo and Dio-rExo + 37,43Gap27. U251s cells were incubated with Dio-stained sExo, rExo and Dio-rExo + 37,43Gap27 for 30 min, then were counterstained with Hoechst 33342 (blue) for 5 min. Dio-stained exosome uptake (green) in cells was observed under fluorescence microscope. Scale bar, 100 µm. Cx43, connexin 43; U251r, temozolomide-resistant U251 glioma cells; U251s, temozolomide-sensitive U251 glioma cells; sExo, exosomes of U251s cells; rExo, exosomes of U251r cells; Dio, dioctadecyloxacarbocyanine.