The in vitro respiratory and acid–base properties of blood and tissue from the Kemp's ridley sea turtle, Lepidochelys kempi

Abstract

We determined the in vitro respiratory and acid–base properties of blood and tissue from Kemp's ridley sea turtles (Lepidochelys kempi). Blood O2 dissociation curves of ridley turtles were sigmoid, with a P50 of 31.2 ± 0.3 (mean ± SD) torr at 25 °C and pH 7.51. Increments in temperature or [Formula: see text] were associated with a shift of the O2 dissociation curves to the right and, hence, a reduction in haemoglobin–O2 binding affinity. The apparent heat of oxygenation, which is a measure of the temperature sensitivity of haemoglobin–O2 affinity, was −10.5 kcal/mol O2. The degree of cooperativity of O2 for hemoglobin binding sites, as measured by the Hill coefficient, increased at higher temperatures (20–30 °C at a [Formula: see text] of 37 torr), but was unaffected by changes in [Formula: see text] (37–52 torr at 25 °C). The CO2-Bohr effect was −0.34 torr/pH unit. The CO2 capacitance coefficient of whole blood and plasma declined as a function of increased [Formula: see text] (22 °C). Non-bicarbonate buffer capacities (22 °C) were 19.7, 18.5, and 6.4 slykes for whole blood, true plasma, and separated plasma, respectively. The skeletal muscle myoglobin content was 3.1 ± 0.84 mg∙g−1 of tissue. The respiratory and acid–base properties of blood and tissue from Kemp's ridley sea turtles are consistent with those of species that utilize lung O2 stores during long-term aerobic dives. The enhanced haemoglobin–O2 temperature sensitivity exhibited by the ridley turtle could be a physiological adaptation for life in coastal environments that typically undergo substantial fluctuations in temperature.

Blood oxygen stores of olive ridley sea turtles, Lepidochelys olivacea are highly variable among individuals during arribada nesting

“…What was most surprising was the striking similarity on VB values between D. coriacea (7.7 ml kg -1 ) and L. olivacea (7.6 ml kg -1 ) sea turtles. This supports previous observations of L. olivacea as being the second-deepest diver (300 m; Stabenau & Heming, 1994) of all species of sea turtles after D. coriacea (1280 m; López-Mendilaharsu, Rocha, Domingo, Wallace, & Miller, 2008). Blood O2 stores may be especially critical if pulmonary shunts are activated as part of the dive response to avoid decompression injuries on the deepest and longest dives (García-Párraga et al, 2018).…”

“…Based on measures of diving behavior in olive ridley sea turtles, blood O2 stores are likely a critical component of aerobic respiration to many dives. Lung stores are similar among species, suggesting that diving differences might be most likely due to individual variation in blood O2 stores rather than in muscle stores, given low myoglobin constants across species; ~4% of total body O2 stores (Berkson, 1966;Lutz & Bentley, 1985;Stabenau & Heming, 1994). Previous investigations reporting deep and long dive behaviors exhibited by olive ridley sea turtles (Chambault et al, 2016;McMahon et al, 2007;Polovina et al, 2004) demonstrated that 77% of dive time represents active foraging behaviors, and that some dives exceed the presumed depths of lung collapse (~120 m, Berkson, 1967).…”

“…Mean dive duration for a large sample of adult females was 46 min. Dives as long as 200 min (3.3 hours) and as deep as 300 m have been reported (Chambault et al, 2016;McMahon et al, 2007;Stabenau & Heming, 1994).…”