Effects of sulfide on K + flux pathways in red blood cells of crucian carp and rainbow trout

Abstract

The effect of sulfide on K + influx pathways was measured in red blood cells (RBCs) of sulfide-sensitive rainbow trout (Oncorhynchus mykiss) and sulfide-tolerant crucian carp (Carassius carassius). In trout RBCs, maximal inhibition of Na + ,K + -ATPase was attained at 10 µmol l −1 sulfide and amounted to 32% without being influenced by pH between 6.7 and 8.3. Ouabain-resistant K + influx in the absence and presence of sulfide was insignificant at pH values between 6.7 and 7.7. At higher pH values ouabain-resistant K + influx increased, but was inhibited to about 15% by 30 µmol l −1 sulfide. In RBCs of crucian carp neither Na + ,K + -ATPase nor ouabain-resistant K + influx were affected by sulfide concentrations up to 850 µmol l −1 . Differences in sulfide-sensitivity of K + influx between both species can be based upon different properties of the membrane transporter themselves. The reduced Na + ,K + -ATPase activity in trout RBCs may also result from a slightly reduced (by 9%) ATP level after sulfide exposure. In addition, intracellular sulfide concentrations were higher in trout RBCs as compared to crucian carp. In trout, intracellular sulfide concentrations reached extracellular levels within 5 min of incubation whereas sulfide concentrations in crucian carp RBCs remained about 2-fold lower than extracellular concentrations. Although the physiological basis of sulfide-insensitive K + influx in crucian carp RBCs is currently unknown it may contribute to the extremely high sulfide-tolerance of this species. Abbreviations: DIOA – R(+)-[(2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]acetic acid; DMSO – dimethylsulfoxide; HEPES – N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid; HCT – haematocrit; PCA – perchloric acid; RBC – red blood cells.