Kinetics of bicarbonate/chloride exchange in dogfish erythrocytes

A stopped-flow rapid reaction apparatus was used to monitor changes in extracellular pH in dogfish (Mustelus canis) erythrocyte suspensions under conditions where dpH/dt was determined by the rate of HCO3-/Cl- exchange across the red cell membrane. Experiments were performed on erythrocytes suspended either in their own plasma or in elasmobranch Ringer solution over a range of temperatures from 5 to 35 degrees C. The exchange fluxes at 25 degrees C for red blood cells suspended in their own plasma (2.03 nmol/cm2-s) or in Ringer solution (2.00 nmol/cm2-s) are not significantly different and can be compared to those obtained under similar conditions for human red cell suspensions (0.910 nmol/cm2-s). The flux for dogfish erythrocytes suspended in Ringer solution was reduced by 80% after exposure of the cells to SITS. An Arrhenius plot of the exchange rate constant yielded an activation energy of about 13.2 kcal/mol. We conclude that 1) plasma has no inhibitory effect of HCO3-/Cl- exchange across the dogfish erythrocyte membrane or on activity of intraerythrocyte carbonic anhydrase, 2) HCO3-/Cl- exchange probably occurs via the same mechanism in fish and mammalian erythrocytes, and 3) the conversion of plasms HCO3- to CO2 in dogfish can be catalyzed by intraerythrocyte carbonic anhydrase.