The action of acid phosphate on the anion permeability of horse erythrocytes.

This study investigates the effects of acid phosphate on the permeability of horse red blood cells (erythrocytes) to bicarbonate ions. The researchers concluded the decreased permeability witnessed is due to the replacement of rapidly diffusing chloride ions by slowly diffusing acid ions, and not to decreased cell permeability.

Background and Methodology

• The research draws upon a 1941 study by Keilin & Mann that detailed an optical method of studying the penetration of erythrocytes by bicarbonate ions and the intracellular activity of carbonic anhydrase.
• This method involves turning the haemoglobin inside the cell into methaemoglobin and observing its transformation from the acidic to alkaline form as bicarbonate ions enter the cell.
• During their initial research, Keilin & Mann observed that this transformation did not take place if the methaemoglobin cells had been washed in acid phosphate, suggesting that acid phosphate influenced the cells’ permeability.
• Further observations by Keilin & Hartree in 1946 suggested that phosphate, phthalate, and citrate buffers of pH 6 might also ‘block’ the anion permeability of these cells.

Study Execution and Findings

• The researchers of this study repeated Keilin & Mann’s and Keilin & Hartree’s optical experiments. They also measured changes in the opacity of cell suspensions and conducted chemical analyses of cells ‘blocked’ by phosphate buffer pH 6.
• They found a consistent relationship between the completeness of the ‘block’ and: a) the amount of phosphate that had penetrated the cells, and b) the amount of chloride that had left the cells.

Conclusions and Implications

• Based on these findings, the researchers suggested that acid buffers’ effects are due to the replacement within the cell of rapidly diffusing chloride ions by slowly diffusing acidic ions, as opposed to decreased cell permeability.
• This implies that acid buffers inhibit the entry of bicarbonate ions into the cell by replacing intracellular anions at a slower rate, thereby greatly reducing the rate of bicarbonate penetration.