A decrease of both [Ca]e and [H]e produces cell damage in the perfused rat heart

Cell damage of the Langendorff-perfused rat heart in response to a decrease of both [Ca²⁺]_e and [H⁺]_e is described. At pH_e = 7.7, lactate dehydrogenase (LDH) release could be induced during perfusion with media of reduced [Ca²⁺]_e (0.1–0.4 mmol/I). Decreasing pH_e to normal abolished LDH release. The gap junction channel blocker heptanol (2 mmol/I) also reduced enzyme release, and polyethylene glycol (9% PEG₆₀₀₀) totally prevented cell damage. Elevation of buffer capacity of perfusion media or perfusion flow both increased LDH release. Cell damage could also be aggravated by substituting 10 mmol/I of [Na⁺]_e by foreign cations. At [Ca²⁺]_e = 0.1 mmol/I and pH_e = 7.7, [Ca²⁺]_i and [Na⁺]_i of non-lysed cells were markedly increased (in HCO₃/CO₂ buffered media to about 7.0 μmol/I and 36 mmol/I, respectively; in HEPES-buffered media, to about 5.0 μmol/I and 55 mmol/l; physiological values of [Ca²⁺]_i and [Na⁺]_i are around 0.1 μmol/I and 10 mmol/I, respectively), whereas pH_i was not appreciably elevated. In contrast to myocytes in the intact heart, [Ca²⁺]_i of isolated cardiomyocytes under similar conditions was decreased to about 75 nmol/I and LDH release was negligible; pH_i of isolated cardiomyocytes, as in intact myocardium, did not change appreciably. The results indicate that Ca²⁺ overload is produced at lowered [Ca²⁺]_e and [H⁺]_e by an influx of Ca²⁺ through gap junctional leaks.