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 oxyqen affinity of suspensions of erythrocytes from juvenile and adult loggerhead (Caretta caretta) and qreen 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 hemoqlobins 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 hemoqlobins in 14.6% CO₂. The P₅₀ of the adult lognerhead 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 profound and profound decreases in pO₂.