Activity of sodium pump in photosnsitized cultured rat cardiomyocytes

Sodium pump (Na⁺/K⁺-ATP-ase) utilizing energy accumulated in macroergic bonds of ATP, maintains physiological sodium and potasium gradients across plasma membrane. This, in turn, preserves cell volume and enables functioning of all Na⁺-gradient driven cotransporters and exchangers. Therefore, any impairment of Na⁺/K⁺-ATP-ase activity results in severe consequences to cell viability. Cardiac cells are equipped with efficient enzymatic machinery capable of coping with oxidative stress. This was the rationale for examining their sodium pump activity upon photosensitization. Cells were incubated with hematoporphyrin dihydrochloride for 1 hour and irradiated using HeNe low-energy laser light (ED: 0.1, 0.3 or 1.0 J/cm²). It was found that Na⁺/K⁺-ATP-ase activity in 3-day-old cardiocytes is indirectly stimulated during photosensitization by rapid influx of sodium. The latter was determined by ratiometric fluorescent probe SBFI/AM. 5-day-old cardiocytes turned out to be less resistant to photooxidative stress as the pump activity was inhibited by 50% in comparison to control cells.