An Analysis of pH Tolerance and Substrate Preference of Isolated Skeletal Muscle Mitochondria from Bufo marinus and Rana catesbeiana

1. The effects of varying pH and substrate on isolated skeletal muscle mitochondria from Bufo marinus and Rana catesbeiana were investigated. 2. For both species, V02 max significantly decreased at all pH\u3c7.3 (P \u3c 0.05), while maximum values were observed at a pH range of 7.3-7.6 with B. marinus maintaining a greater V02 max than R. catesbeiana. 3. Respiratory control values (RCR) decreased significantly at all pH \u3c 6.9 for both species (P \u3c 0.05) 4. Isolated mitochondria from both species were maintained at pH = 7.2 and O2 consumption measured under five separate substrate conditions. 5. A rank preference was established based upon state 3 and RCR values. 6. Substrate preference was identical for both species and interspecific comparisons revealed differences in state 3 respiration and coupling

A Metabolic Hypothesis for the Evolution of Temperature Effects on the Arterial PCO2 and pH of Vertebrate Ectotherms

Body temperature increases in ectothermic vertebrates characteristically lead to both increases in arterial PCO2 (PaCO2) and declines in resting arterial pH (pHa) of about 0.017 pH units/°C increase in temperature. This ‘alphastat’ pH pattern has previously been interpreted as being evolutionarily-driven by the maintenance of a constant protonation state on the imidazole moiety of histidine protein residues, hence stabilizing protein structure-function. Analysis of the existing data for interclass responses of ectothermic vertebrates show different degrees of PaCO2 increases and pH declines with temperature between the classes with reptiles\u3eamphibians\u3efish. The PaCO2 at the temperature where maximal aerobic metabolism (VO2max) is achieved is significantly and positively correlated with temperature for all vertebrate classes. For ectotherms, the PaCO2 where VO2max is greatest is also correlated with VO2max indicating there is an increased driving force for CO2 efflux that is lowest in fish, intermediate in amphibians and highest in reptiles. The pattern of increased PaCO2 and the resultant reduction of pHa to increased body temperature would serve to increase CO2 efflux, O2 delivery, blood buffering capacity and maintain ventilatory scope. This represents a new hypothesis for the selective advantage of arterial pH regulation from a systems physiology perspective in addition to the advantages of maintenance of protein structure-function

The Return to Final Paper Examining in English National Curriculum Assessment and School Examinations: Issues of Validity, Accountability and Politics

There are sound educational and examining reasons for the use of coursework assessment and practical assessment of student work by teachers in schools for purposes of reporting examination grades. Coursework and practical work test a range of different curriculum goals to final papers and increase the validity and reliability of the result. However, the use of coursework and practical work in tests and examinations has been a matter of constant political as well as educational debate in England over the last 30 years. The paper reviews these debates and developments and argues that as accountability pressures increase, the evidence base for published results is becoming narrower and less valid as the system moves back to wholly end-of-course testing

Anuran Amphibians as Comparative Models for Understanding Extreme Dehydration Tolerance: A Unique Negative Feedback Lymphatic Mechanism for Blood Volume Regulation

Anurans are the most terrestrial order of amphibians. Couple the high driving forces for evaporative loss in terrestrial environments and their low resistance to evaporation, dehydration is an inevitable stress on their water balance. Anurans have the greatest tolerances for dehydration of any vertebrate group. Some species can tolerate evaporative losses up to 45% of their standard body mass. Anurans have remarkable capacities to regulate blood volume with hemorrhage and dehydration compared with mammals. Stabilization of blood volume is central to extending dehydration tolerance, since it avoids both the hypovolemic and hyperviscosity stresses on cardiac output and its consequential effects on aerobic capacity. Anurans, in contrast to mammals, seem incapable of generating a sufficient pressure difference, either oncotically or via interstitial compliance, to move fluid from the interstitium into the capillaries. Couple this inability to generate a sufficient pressure difference for transvascular uptake to a circulatory system with high filtration coefficients and a high rate of plasma turnover is the consequence. The novel lymphatic system of anurans is critical to a remarkable capacity for bloodvolume regulation. This review summarizes what is known about the anatomical and physiological specializations that are involved in explaining differential blood volumeregulation and dehydration tolerance involving a true centrally mediated negative feedback of lymphatic function involving baroreceptors as sensors and lymph hearts, arginine vasotocin, pulmonary ventilation and specialized skeletal muscles as effectors

Ecological and environmental physiology of amphibians volume 1

xii, 469 p.; 24 c

The Spleen as an Unlikely Source of red blood cells during activity in fishes

Letter. We read with interest the paper by Brijs et al. (2020) regarding the ‘blood-boosting’ properties apparently exhibited by the Antarctic notothenioid fish (Pagothenia borchgrevinki). Although the data provide additional insights into the physiology of an extreme cold-adapted fish, we believe the authors have drawn erroneous conclusions about the mechanisms involved with this ‘blood-boosting’ phenomenon. The authors conclude that the spleen sequesters enough red blood cells (RBCs) to increase the haematocrit (Hct) and, therefore, blood oxygen carrying capacity in fed and exercise states. Further, the authors posit the spleen holds these RBCs in reserve to reduce blood viscosity until additional oxygen is needed to support increases in metabolic rate. In our view, the increases in Hct in P. borchgrevinki can be primarily explained by an alternative mechanism that the authors did not consider in their analysis: elevated blood pressure increases plasma efflux from the vascular to the interstitial space, thus increasing the fraction of RBCs in the vascular space (i.e. Hct). We present two arguments against a role for the spleen in providing a significant contribution to increased Hct in P. borchgrevinki. Our first argument is based on the principle of conservation of mass. Brijs et al. (2020) used uninstrumented fish to examine changes in spleen volume at rest, after feeding and following enforced exercise. The comparisons are partly confounded by significant differences in body mass between groups. We have plotted the authors\u27 data for unfed and fed animals in resting and exercised states to show the significant relationships between spleen mass and body mass. If we compare a 74 g fish for both groups, spleen mass for resting fish is 0.365 g and is 0.213 g after exercise (Δ spleen mass=0.152 g). Can this change in spleen mass account for the changes in Hct observed by the authors? If we assume a blood volume of 5% of body mass, for a 74 g fish blood volume is 3.7 g (=3.7 ml, assuming blood has a density of 1 g ml−1). The average Hct was 15.8% and 27.1% for resting and exercised fish, respectively. The mass of RBCs for this blood volume is therefore 0.585 g (rest) and 1.003 g (exercise) with a difference of 0.418 g (ml). It is clear that changes in spleen volume cannot account for the mass of RBCs added to the vascular space during exercise. The changes in spleen mass account for approximately 36% of the change in RBC mass with the remaining 64% of RBC unaccounted for; with unfed fish, Hct changes from 8.6% to 25.1% and the non-splenic contribution is larger (76%). We also note that for resting fish (unfed vs fed), Hct increased from ∼9% to ∼21%, but absolute spleen mass increased, rather than decreased, a further indication that non-splenic mechanisms account for the increased Hct