Passive calcium movements in dog red blood cells: anion effects.

Calcium influx in dog red blood cells was stimulated by replacing chloride in the medium with nitrate or thiocyanate. These anion effects were due to stimulation of a sodium-dependent calcium pathway, because calcium influx in the presence of nitrate or thiocyanate was 1) inhibited by external sodium, 2) dependent on internal sodium, 3) inhibited by cell shrinkage and low pH, and 4) inhibited by quinidine. All these characteristics had previously been shown to hold for calcium movements in the presence of chloride. Neither nitrate nor thiocyanate caused an irreversible change in calcium transport in the concentrations studied. Calcium-stimulated sodium efflux is stimulated when chloride is replaced by thiocyanate but not by nitrate. Several limiting features of the system are discussed, which preclude a conclusive interpretation of the data. The possibility is considered that the rates of sodium-dependent calcium transport in the presence of chloride, nitrate, and thiocyanate are a function of the conductance of these anions.