The teleost pseudobranch: a role for preconditioning of ocular blood supply?

The physiological relevance of the teleost pseudobranch as a remnant of a reduced gill arch is still unclear. Numerous hypotheses have been proposed regarding its physiological role, but direct confirmatory evidence is lacking. The close relationship by serial blood flow arrangement with the fish eye's choroid rete has sparked the idea that pseudobranchial preconditioning of blood pH may facilitate initiation of the Root effect and thus support the establishment of high oxygen tensions for retinal diffusive supply.

Two different oxygen sensors regulate oxygen-sensitive K+ transport in crucian carp red blood cells.

The O2 dependence of ouabain-independent K+ transport mechanisms has been studied by unidirectional Rb+ flux analysis in crucian carp red blood cells (RBCs). The following observations suggest that O2 activates K+-Cl- cotransport (KCC) and deactivates Na+-K+-2Cl- cotransport (NKCC) in these cells via separate O2 sensors that differ in their O2 affinity. When O2 tension (PO2) at physiological pH 7.

Determination of pH by microfluorometry: intracellular and interstitial pH regulation in developing early-stage fish embryos (Danio rerio).

Microfluorometric techniques were applied in vivo for continuous monitoring of specific acid-base parameters in zebrafish (Danio rerio) embryos during early stages of ontogeny. Dextran-coupled pH-sensitive single-excitation/dual-emission dye SNARF-1 was pressure-injected into individual cells or the interstitial space of 16- to 256-cell embryos, and pH was continuously recorded during subsequent development for time periods of up to 8 h. A novel calibration technique was developed, essentially characterized by in vitro inorganic buffer calibration of the optical system and mathematical post-processing according to the effects of in vivo dye modifiers through a correlation established by direct comparison of optical techniques with pH microelectrodes.

Oxygen delivery to the fish eye: root effect as crucial factor for elevated retinal PO2.

Although the retina has one of the highest metabolic rates among tissues, certain teleost fishes lack any vascular supply to this organ which, in combination with the overall thickness of the organ, results in extremely long diffusion distances. As the only way to compensate for these obstacles, oxygen partial pressure (PO2) in the eyes of such fish is elevated far above atmospheric values. Although not supported by any direct evidence, the enhancement of PO2 is considered to be related to the Root effect, the release upon acidification of Hb-bound O2 into physical dissolution, possibly supported by counter-current multiplication similar to the loop of Henle.

Buffering and H+ ion dynamics in muscle tissues.

After anaerobic activity with release of large quantities of intermediary metabolic end products, further energy production critically depends on rapid elimination of H+ ions from the muscle tissues to secure key enzymatic activities. The involved processes, interactions and interrelationships of mechanisms have been analyzed on the basis of a physiological model and available experimental data. The H+ elimination from muscle tissue is a multifactorial process primarily governed by the capillary H+ transport capacitance, effected by buffering capabilities of intracellular and capillary fluids compartments, by dynamically interrelated regulation of intracellular and extracellular pH, by the magnitude and quality of convective perfusional transfer and further factors.

O(2)-dependent K(+) fluxes in trout red blood cells: the nature of O(2) sensing revealed by the O(2) affinity, cooperativity and pH dependence of transport.

The effects of pH and O(2) tension on the isotonic ouabain-resistant K(+) (Rb+) flux pathway and on haemoglobin O2 binding were studied in trout red blood cells (RBCs) in order to test for a direct effect of haemoglobin O(2) saturation on K(+) transport across the RBC membrane. At pH values corresponding to in vivo control arterial plasma pH and higher, elevation of the O(2) partial pressure (PO(2)) from 7.8 to 157 mmHg increased unidirectional K(+) influx across the RBC membrane several-fold.

Effects of anoxia on intracellular free Ca2+ in isolated cardiomyocytes from turtles.

One of the most important negative consequences of hypoxic stress in the mammalian myocardium is a breakdown in intracellular calcium homeostasis. This study examines the effects of anoxic stress on intracellular calcium regulation in isolated ventricular myocytes from a hypoxia tolerant vertebrate, the western painted turtle (Chrysemys picta bellii). Isolated calcium tolerant cardiomyocytes from turtle hearts were mounted on a glass cover slip that formed the bottom of a sealed, Plexiglas perfusion chamber.

Analysis of cardiac shunting in the turtle Trachemys (Pseudemys) scripta: application of the three outflow vessel model.

Blood distribution within the ventricle was analysed in acutely prepared turtles Trachemys scripta by measuring the oxygen concentration and flow rates of blood in the central vessels. Pulmonary (Qp) and systemic (Qs) blood flow rates were similar when total cardiac output (Qtot) was below 40 ml min-1 kg-1. Above this value, increments of Qtot were directed to the pulmonary circuit, with Qs levelling off at approximately 20 ml min-1 kg-1.

The mechanism of cardiac shunting in reptiles: a new synthesis.

The mechanism of cardiac shunting in reptiles is controversial. Recent evidence suggests that a right-to-left shunt in turtles results primarily from a washout mechanism. The mechanism that accounts for left-to-right (L-R) shunting is unresolved.

Extracellular and intracellular carbon dioxide concentration as a function of temperature in the toad Bufo marinus.

Previous studies of reptiles and amphibians have shown that changing the body temperature consistently produces transient changes in the respiratory exchange ratio (RE) and, hence, changes in whole-body CO2 stores, and that the extracellular fluid compartment contributes to the temperature-related changes in CO2 stores. The purpose of this study was to determine whether the intracellular fluid compartment contributes to the changes in CO2 stores in undisturbed resting cane toads. Increasing body temperature from 10 to 30 degrees C temporarily elevated RE, and returning body temperature to 10 degrees C temporarily lowered RE.

Site of acid-base relevant ion transfer in the gills of rainbow trout (Oncorhynchus mykiss) exposed to environmental hypercapnia.

In order to delineate the contribution of primary vs. secondary circulatory circuits in the gill for acid-base and ionic regulation, the flow and composition of the fluids in the central venous sinus (CVS) and the systemic circuit of rainbow trout were studied by application of a previously developed microcannulation technique during normocapnic and hypercapnic conditions. The average haematocrit (Hct) of blood from dorsal aorta (DA) and sinus venosus (SV) ranged from 20.

Effect of chronic hypoxia on hemodynamics, organ blood flow and O2 supply in rats.

Aortic blood flow, heart rate, blood pressure and blood flow distribution were measured in 10 chronically hypoxic rats (3 weeks, PB 370-380 Torr) breathing 10% O2 (chronic hypoxia) and after 30 min of breathing air (acute normoxia). Controls were 10 normoxic littermates breathing air (normoxia) and 10% O2 for 30 min (acute hypoxia). Acute hypoxia resulted in increased aortic blood flow and heart rate, and decreased total peripheral resistance.

Changes in regional blood flow distribution and oxygen supply during hypoxia in conscious rats.

The effects of acute hypoxia on central hemodynamics, regional blood flow, and regional oxygen supply (blood flow x arterial O2 concentration) were studied in conscious resting rats. Regional blood flow was determined by the radiolabeled microsphere technique. Blood pressure, heart rate; and aortic blood flow increased and total peripheral resistance decreased significantly during hypoxia.

Regional blood flow in conscious resting rats determined by microsphere distribution.

To determine organ blood flow in the resting state, a box was designed to keep conscious untrained rats minimally disturbed. Blood pressure, heart rate, and organ blood flow, determined by the microsphere distribution and reference sampling technique, were measured in 11 Sprague-Dawley rats. After an acclimation period, 15-microns-diameter microspheres labeled with 113Sn were infused into the ascending aorta, a reference blood sample was withdrawn from the caudal artery, and organ blood flows were computed according to standard procedures.

Interrelationships between red cell nucleoside triphosphate content, and blood pH, O2-tension and haemoglobin concentration in the carp, Cyprinus carpio.

As a starting point for investigations of possible control factors for the nucleoside triphosphate content in carp red cells, we utilized the natural variability in blood physico-chemical parameters to test for interrelationships. By application of two-variable regression analysis, the red cell NTP content was found to be significantly correlated with arterial PO 2 and pH as well as with the blood haemoglobin (Hb) concentration. These correlations show a rise in red cell NTP content with falling pH as well as with falling Hb concentration, whereas a decrease in PO 2 was associated with a decrease in the content of NTP, particularly at low PO 2 values.

Spatial and temporal variability of blood flow in stimulated dog gastrocnemius muscle.

The distribution of blood flow in skeletal muscle stimulated to rhythmic isotonic contractions was studied by injections of radioactive microspheres into the arterial supply of gastrocnemius muscles (mean weight 88 g) subsequently cut into 0.5 g pieces for determination of radioactivity. The coefficient of variation (CV = SD/mean) of the ratio of simultaneously injected 10 microns and 15 microns microspheres, 0.

Blood flow distribution and its temporal variability in stimulated dog gastrocnemius muscle.

The distribution of blood flow in skeletal muscle stimulated to rhythmic isotonic contractions was studied by injections of radioactive microspheres into the arterial supply in 8 gastrocnemius muscles (mean weight 84 g) of 6 anesthetized dogs (20-25 kg body weight). The distribution of 10 micron microspheres in regions of about 0.5 g was very similar to that of the standard 15 micron microspheres, whereas that of 25 micron microspheres was more uneven.

In vivo analysis of partitioning of cardiac output between systemic and central venous sinus circuits in rainbow trout: a new approach using chronic cannulation of the branchial vein.

Freshwater-acclimated rainbow trout were chronically and non-occlusively cannulated in the dorsal aorta (DA), sinus venosus (SV) and branchial vein (BV), the latter returning the blood perfusing the central venous sinus (CVS) of the gill after being shunted away from the systemic circuit. After recovery, blood samples from these three sites were analysed for haematocrit (Hct) and [Hb]. Branchial venous blood was found to have considerably lower Hct and [Hb] (Hct = 3.

Blood flow patterns in the salamander, Ambystoma tigrinum, before, during and after metamorphosis.

The patterns of blood flow through the complex circulation of the tiger salamander, Ambystoma tigrinum, were investigated during aquatic normoxia and hypoxia by application of the microsphere technique. The distribution of differently labelled microspheres injected into the bloodstream towards the left and right atria, respectively, was used to evaluate the role of the ductus arteriosus in lung perfusion before, during and after metamorphosis, as well as the general contribution of right and left atrial outputs to the blood flow in gills and lungs in neotenic and postmetamorphic animals. The distribution patterns of radioactive microspheres among pulmonary, branchial and systemic tissues indicated that the ductus arteriosus is the major pulmonary perfusion pathway in neotenic and metamorphosing animals, whereas after metamorphosis the main perfusion pathway is down the entire length of the pulmonary artery.

Regulation of ventilation and acid-base status in the elasmobranch Scyliorhinus stellaris during hyperoxia-induced hypercapnia.

Exposure of the elasmobranch Scyliorhinus stellaris to environmental hyperoxia (PO2 of 500 mm Hg) resulted in a considerable rise of arterial PCO2 from 1.9 mm Hg during normoxia to about 11 mm Hg after 6 days as an expression of the primarily oxygen-oriented regulation of gill ventilation. In contrast to the typical pattern during environmental hypercapnia, however, arterial plasma pH was hardly affected by the considerable hyperoxia-induced hypercapnia.

Analysis of intracardiac shunting in the lizard, Varanus niloticus: a new model based on blood oxygen levels and microsphere distribution.

The central sites of the cardiovascular system (right and left aortic arches, RAo and LAo, pulmonary artery, PA, and right and left atria, RAt and LAt) were chronically and non-occlusively cannulated for an analysis of intracardiac shunting in Varanus niloticus. Oxygen partial pressure (PO2) and oxygen concentration (CO2) were significantly higher in right aortic blood than values determined in left aortic blood. The difference was larger in animals acclimated to 25 degrees C (RAo CO2 = 4.

Acid-base regulation and blood gases in the anuran amphibian, Bufo marinus, during environmental hypercapnia.

Specimens of Bufo marinus were exposed to aerial and aquatic hypercapnia (5% CO2) in a closed, water recirculation system to evaluate mechanisms involved in the compensation of a respiratory acidosis in these animals. Arterial PCO2 was elevated from about 9 mmHg (1 mmHg = 133.3 Pa) to 35 (1 h) and 37 mmHg (2 h), and gradually approached about 40 mmHg (24 h of hypercapnia).

In vivo measurements of tissue pH of the heart, brain, liver, spleen, and skeletal muscle following therapy of severe metabolic uraemic acidosis with infusion of bases: an experimental study on the limitation of the Mellemgaard-Astrup equation.

The intracellular tissue pH of the heart, brain, liver, spleen, and skeletal muscle of nephrectomized rats was determined in vivo from the distribution of 14C-labelled DMO (5,5-dimethyl-2-4-oxazolidinedione) following acute variation of arterial plasma pH (pHe) by CO2 inhalation or sodium bicarbonate administration in the range of pHe 6.9-7.7, or following correction of severe metabolic uraemic acidosis with sodium bicarbonate or Tris (hydroxymethyl) aminomethane (THAM) infusion according to the Mellemgaard-Astrup equation.

Effects of nitrite exposure on blood respiratory properties, acid-base and electrolyte regulation in the carp (Cyprinus carpio).

Adult carp were subjected to 1 mM environmental nitrite for 48 h and nitrite uptake and changes in blood respiratory properties, extracellular electrolyte composition and acid-base status were examined. A constant influx of nitrite caused an accumulation of NO2- in plasma to 5.4 mM in 48 h.