Detailed Solution Composition for Cell Contractions

The composition of all solutions in this study is summarized as follows. Normal Krebs solution contained the following (in mM): 120 NaCl, 5.9 KCl, 25 NaHCO₃, 1.2 NaH₂PO₄, 11.5 dextrose, 2.5 CaCl₂, 1.2 MgCl₂ (Biosharp, China). High KCl solution (96 mM) was prepared as normal Krebs but with equimolar substitution of NaCl with KCl. Oxytocin (MedChemExpress, China) was dissolved in deionized water to prepare 10^-11 to 10^-6 M concentration for isometric contractions. Digestion solution was prepared: 2 mg/ml type II collagenase, 1 mg/ml BSA, and 0.5 mg/ml deoxyribonuclease I was dissolved in Dulbecco’s Modified Eagle Medium (DMEM) (Sigma-Aldrich, American). The normal glucose medium consisted of DMEM with 5.5 mmol/L glucose, 10% fetal bovine serum (FBS) (Sigma-Aldrich, American), and 1% penicillin/streptomycin (Gibco, American) solution. The high glucose medium consisted of DMEM with 25 mmol/L glucose, 10% FBS, and 1% penicillin/streptomycin solution. CoCl₂ medium was prepared in normal glucose containing 200 µmol/L CoCl₂ (Sigma-Aldrich, American). High glucose with echinomycin medium was prepared in high glucose containing 10 nmol/L echinomycin (MedChemExpress, China). CoCl₂ with echinomycin medium was prepared in CoCl₂ medium containing 10 nmol/L echinomycin. CoCl₂ with L-methionine medium was 10 µmol/L L-methionine (Sigma-Aldrich, American) dissolved in CoCl₂ medium. High glucose with L-methionine medium was 10 µmol/L of L-methionine dissolved in high glucose medium. High KCl (96 mM) and oxytocin (10^-7 M) were dissolved in the respective medium for cell contractions.