Physiological consequences of oxygen-dependent chloride binding to hemoglobin.

The PO(2)-dependent binding of chloride to Hb decreases the Cl(-) concentration of the red blood cell (RBC) intracellular fluid in venous blood to approximately 1-3 mmol/l less than that in arterial blood. This change is physiologically important because 1) Cl(-) is a negative heterotropic allosteric effector of Hb that competes for binding sites with 2,3-bisphosphoglycerate and CO(2) and decreases oxyhemoglobin affinity in several species; 2) it may help reconcile several longstanding problems with measured values of the Donnan ratios for Cl(-), HCO, and H(+) across the RBC membrane that are used to calculate total CO(2) carriage, ion flux rates, and membrane potentials; 3) it is a factor in the change in the dissociation constant for the combined nonvolatile weak acids of Hb associated with the Haldane effect; and 4) it diminishes the decrease in strong ion difference in the RBC intracellular fluid that would otherwise occur from the chloride shift and prevent the known increase of HCO concentration in that compartment.

CO2 and heat have different effects on directed ventilation behavior of grasshoppers Melanoplus differentialis.

We tested the hypothesis that CO2 and heat have different effects on the ventilatory pattern of grasshoppers Melanoplus differentialis. Eight grasshoppers were sealed between rostral (inspiratory) and caudal (expiratory) spiracles in separated, airtight, chambers and pressure changes were measured. Normal breathing patterns decreased pressure in the rostral chamber and increased pressure in the caudal chamber (i.e. unidirectional pumping rostral to caudal). Insects exposed to ventilatory stimulation by CO2 or heat significantly increased pumping frequency from 26+/-2 (+/-S.E.M.) at 0% CO2 to 54+/-6 breaths/min at 8% CO2 (at 30 degrees C), and from 27+/-3 at 30 degrees C to 44+/-4 breaths/min at 45 degrees C. Unidirectional pumping failed to change with increased CO2 concentration and increased significantly with heat exposure. Thus, while CO2 only increased pumping frequency, heat increased pumping frequency and unidirectional pumping.

Respiratory responses to acute heat stress in cranes (Gruidae): the effects of tracheal coiling.

Some species of cranes have extensive coiling of their trachea that substantially increases their anatomical dead space. We subjected individuals of four species of cranes (Anthropoides virgo, Balearica regulorum, Grus grus and Grus japonensis) to acute heat stress to investigate the effectiveness of this trait as a thermoregulatory adaptation. We measured cloacal temperature, respiratory flow and frequency and arterial pH during normothermic breathing and thermal panting. Extra tracheal length appears to be a helpful but nonessential adaptation to prevent cranes from becoming alkalotic while panting. Cranes in our study had relatively lower panting frequencies and greater tidal volumes than have been reported for other birds subjected to heat stress. Tracheal coiling is probably more important to vocalization than to respiration or thermoregulation.

Ventilatory response to inspired CO2 in the sea turtle: effects of body size and temperature.

The ventilatory response of green turtles (Chelonia mydas) to inspired CO2 was tested. Both immature (0.9--1.35 kg) and adult (59--130 kg) animals responded with increased ventilation (VE) that was primarily (immature) or exclusively (adult) due to increased respiratory frequency. The VE of the immature turtles while breathing air increased with temperatures between 15 and 35 degrees C with a Q10 of 1.95, but the peak VE of these turtles while breathing 4.5% CO2 in air was not significantly different at 15, 25 or 35 degrees C. VE increased irregularly with time throughout an hour of CO2 breathing in both groups, although several of the adult animals exhibited a first-breath response to CO2 and all animals increased VE within 5 min after the onset of CO2 breathing. The VE of an immature turtle at 35 degrees C increased with graded increases in CO2 up to 6%, but at 15 and 25 degrees C VE increased only up to 4.5% and decreased with 6% CO2. The results are discussed in terms of possible receptor mechanisms involved.

Ventilation, gas exchange and metabolic scaling of a sea turtle.

Ventilation of green turtles (Chelonia mydas) was affected by the position in which the animal was placed: supine animals breathed slowly 0.07 breaths/min) and deeply (8.0 L/breath); prone animals breathed more rapidly (0.43 breaths/min) and more shallowly (3.5 L/breath). From the respiratory exchange ratio and other indicators it appears that green turtles hyperventilate during exercise and hypoventilate during recovery. O2 consumption of the resting sea turtle (0.024 L-kg-1-h-1) is similar to that of other large turtles. Maximal O2 consumption (0.25L-kg-1-h-1) is greater than that of other large turtles. Minimal O2 consumption scaled in proportion to the -0.17 power of the body mass of green turtles over the range of 0.030 to 141.5 kg. The maximal O2 consumption scaled in proportion to the -0.06 power of body mass for the same range of body masses.

Energetics of swimming of a sea turtle.

Young (mean mass 735 g) green turtles (Chelonia mydas) were able to swim in a water channel at sustained speeds between 0-14 and 0-35 m.s-1. Oxygen consumption at rest was was 0-07 l.kg-1.h-1; at maximum swimming speed oxygen consumption was 3-4 times greater than at rest for a given individual. In comparison with other animals of the same body mass the cost of transport for the green turtle (0.186lO2.kg-1.km-1) is less than that for flying birds but greater than that for fish. From drag measurements it was calculated that the aerobic efficiency of swimming was between 1 and 10%; the higher efficiencies were found at the higher swimming speeds. Based upon the drag calculations for young turtles, it is estimated that adult turtles making the round-trip breeding migration between Brazil and Ascension Island (4800 km) would require the equivalent of about 21% of their body mass in fat stores to account for the energetic cost of swimming.