A decrease of both [Ca2+]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/l). Decreasing pH(e) to normal abolished LDH release. The gap junction channel blocker heptanol (2 mmol/l) also reduced enzyme release, and polyethylene glycol (9% PEG(6000)) 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/l of [Na+](e) by foreign cations. At [Ca2+](e) = 0.1 mmol/l and pH(e) = 7.7, [Ca2+](1) and [Na+](1) of non-lysed cells were markedly increased (in HCO3/CO2 buffered media to about 7.0 mu mol/l and 36 mmol/l, respectively; in HEPES-buffered media, to about 5.0 mu mol/l and 55 mmol/l; physiological values of [Ca2+](1) and [Na+](1) are around 0.1 mu mol/l and 10 mmol/l, respectively), whereas pH(1) was not appreciably elevated. In contrast to myocytes in the intact heart, [Ca2+](1) of isolated cardiomyocytes under similar conditions was decreased to about 75 nmol/l and LDH release was negligible; pH(1) 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.