Potassium transmembrane fluxes in anoxic hepatocytes from goldfish (Carassius auratus L.)

Despite the fact that anoxic goldfish hepatocytes can maintain the transmembrane gradients of Na+, H+ and Ca2+, cyanide (CN) intoxication leads to a rapid breakdown of K+ homeostasis. In this study, [86Rb+] K+ fluxes across the plasma membrane of goldfish hepatocytes were studied in order to identify the possible causes of this imbalance. Four minutes of cyanide incubation induced an acute and stable 61% decrease of K+ influx (mostly driven by Na,K-ATPase activity), whereas K+ efflux increased by 24.3%, this imbalance yielding a net K+ efflux of 0.279 ± 0.024 nmol 10−6 cells−1 min−1. This uncoupling was not observed when glycolytic ATP production was inhibited with iodoacetic acid. Although the CN-induced decrease of K+ influx was fully reversible upon washout of the inhibitor, it could not be prevented by any of the following treatments: (1) addition of 2% bovine serum albumin, which binds extracellular fatty acids known to activate specific K+ channels; (2) addition of ascorbate, which acts as a radical scavenger; (3) inclusion of 5 mM glucose as an extracellular carbon source; and (4) removal of medium oxygen (obtained by nitrogen bubbling). Regarding the elevation of K+ efflux in the presence of CN, neither ATP-dependent K+ channels nor the KCl cotransporter appeared to be activated, whereas BaCl2, an inhibitor of voltage-gated K+ channels, decreased K+ efflux of CN-intoxicated cells to control levels. In summary, these results indicate that, in goldfish hepatocytes, the CN-induced K+ imbalance results from acute Na,K-ATPase inhibition together with the activation of voltage-dependent K+ channels, the latter probably resulting from transient membrane depolarization.