Isolation of human atrial or ventricular cells        

1. Human tissue was derived from atrial or ventricular biopsy specimens belonging to patients undergoing heart surgery.
2. Isolated myocardial tissue was cut into 1- to 2-mm3 pieces.
3. Isolated myocardial tissue was washed with Ca²⁺ -Mg²⁺–free phosphate-buffered solution (PBS).
4. Isolated myocardial tissue was digested three times for 5 minutes at 37°C with 0.2% trypsin and 0.1% collagenase IV.
5. The obtained cells were discarded, and the remaining tissue fragments washed with primary cell culture medium and primary cell culture supplemented with 10% fetal calf serum, 100 U/mL penicillin G, 100 µg/mL streptomycin, and 2 mmol/L L-glutamine were cultured at 37°C and 5% CO_².
6. Twenty-four hours later, the medium was again replaced with primary cell medium and supplement.