Because myocardial vascularization is absent at this stage and oxygen requirement must be met exclusively by diffusion, the hearts were maintained in close contact with and slightly flattened by the membrane to minimize diffusional barriers. Thus, PO2 at the tissue level could be strictly controlled by flushing high-grade gas of selected composition at a rate of 20 mL/min through the gas compartment to modify the composition of the gas within less than 1 s. The hearts were made normoxic with air (PO2=19 kPa under these experimental conditions) or anoxic with 100% pure nitrogen. Additionally, the hearts could be submitted to an adjustable linear oxygen ramp decreasing or increasing within the range of 0 to 9.3 kPa at a rate of ±67 Pa/s. The ramping technique consisted of mixing a constant flow of pure nitrogen with a flow of air adjustable through a remote-controlled tap. These flows were monitored by two highly sensitive airflow sensors (AWM2100V, Honeywell, Freeport, Illinois, USA) connected to an Apple Macintosh computer. If you want to make your online shopping advantageous and safe, check out the best pharmacy to buy Claritin online tablets without any need for a prescription, any time of the day or night with straight to the doorstep delivery.
The chamber was mounted onto the stage of an inverted microscope (IMT-2 Olympus, Olympus Optical, Tokyo, Japan) equipped with a thermostabilized incubator (37.5°C).
The composition of the culture medium was (in mmol/L) 100 NaCl, 2 KCl, 0.75 CaCl2.2H2O, 0.78 MgCl2.6H2O, 10.7 Na2HPO4.2H2O, 2.7 KH2PO4, 8 glucose (pH 7.35; 235 mosmol/kgH2O). The buffering capacity of this solution was 6.93 |imoles H+/(mL.ApH 1).