Regulation of hemoglobin function and whole blood oxygen affinity by carbon dioxide and pH in the loggerhead (Caretta caretta) and green sea turtle (Chelonia mydas mydas).

Abstract

The oxygen affinity of suspensions of erythrocytes from juvenile and adult loggerhead (Caretta caretta) and green sea (Chelonia mydas mydas) turtles decreased markedly with increasing concentrations of carbon dioxide (0 to near 15%) or hydrogen ion (pH 7.6 to pH 7.2). The P50's were higher with increases in pCO2, particularly at pH near 7.4, than were the P50's with increases in hydrogen ion concentration at any given CO2 concentration. Solutions of hemoglobins from the juvenile loggerhead (8-9 mos.) and green sea (10 mos.) turtles responded to 2, 3-DPG, ATP, or inositol-P5 when added at molar ratios of phosphate to hemoglobin of 4:1 and 20:1 in 0% and 6.29% CO2 but showed no decrease in oxygen affinity at these two CO2 levels in the green turtle when the molar ratio of phosphate to hemoglobin was 0.4. These compounds had little effect on the P50 of these hemoglobins in 14.6% CO2. The P50 of the adult loggerhead turtle hemoglobin did not increase in the presence of organic phosphates beyond the effect induced by CO2 alone. The P50 of hemoglobin from the adult green sea turtle increased only slightly when the molar ratio of phosphate to hemoglobin was 20:1 and at 0 and 6% CO2 concentration; little effect was observed at 14.6% CO2. These data demonstrate that blood oxygen affinities and hemoglobin function in these two species of marine turtles are altered significantly by CO2 and to a lesser degree by pH. It is suggested that such alterations may be of significance in vivo during prolonged diving when there are dramatic rises in blood pCO2 and [H+] and profound decreases in pO2.