Effects of changes in pO2, pCO2 and pH on the total vascular resistance of perfused cat kidneys

TWIK-Related Acid-Sensitive Potassium Channels (TASK-1) Emerge as Contributors to Tone Regulation in Renal Arteries at Alkaline pH

Aim: TASK-1 channels are established regulators of pulmonary artery tone but their contribution to the regulation of vascular tone in systemic arteries is poorly understood. We tested the hypothesis that TASK-1 channel functional impact differs among systemic vascular beds, that this is associated with differences in their expression and may increase with alkalization of the extracellular environment. Therefore, we evaluated the expression level of TASK-1 channels and their vasomotor role in mesenteric and renal arteries.

Methods: Pulmonary, mesenteric and renal arteries from male Wistar rats were used for TASK-1 channel mRNA (qPCR) and protein content (Western blotting) measurements. The functional role of TASK-1 channels was studied by wire myography using the TASK-1 channel blocker AVE1231. In some experiments, the endothelium was removed with a rat whisker.

Results: Expression levels of both mRNA and protein of the TASK-1 channel pore-forming subunit were highest in pulmonary arteries, lowest in mesenteric arteries and had an intermediate value in renal arteries. Blockade of TASK-1 channels by 1 µM AVE1231 increased U46619-induced contractile responses of pulmonary arteries but did not affect basal tone and contractile responses to methoxamine of mesenteric and renal arteries at physiological extracellular pH (pHo = 7.41). At alkaline extracellular pH = 7.75 (increase of NaHCO3 to 52 mM) AVE1231 evoked the development of basal tone and increased contractile responses to low concentrations of methoxamine in renal but not mesenteric arteries. This effect was independent of the endothelium.

Conclusion: In the rat systemic circulation, TASK-1 channels are abundant in renal arteries and have an anticontractile function under conditions of extracellular alkalosis.

Skeletal muscle oxygen availability during respiratory acid-base disturbances in cats

Respiratory acid-base disorders elicit physiological responses that alter O2 delivery to various tissues. We have used a near infrared (NIR) optical technique to monitor cytochrome a,a3 oxidation state, tissue O2 store (relative hemoglobin plus myoglobin oxygenation), and regional blood volume in intact resting skeletal muscle during respiratory acid-base disturbances in anesthetized cats. Hypercapnic acidosis and hypocapnic alkalosis were produced in separate groups of animals by ventilation with increasing concentrations of CO2 (n = 13) or hyperventilation (n = 8). Respiratory acidosis decreased oxygen availability to hindlimb muscle while respiratory alkalosis did not change tissue oxygenation. Inspired CO2 progressively decreased muscle blood volume, cytochrome a,a3 oxidation level, and muscle oxygen store. These optical responses were greatly attenuated both by pre-treatment with bretylium and by hemorrhagic hypotension, suggesting mediation through sympathetic vasoconstriction. Metabolic acidosis, produced by intravenous HCl infusion (n = 8), did not reproduce the hindlimb optical responses mediated by CO2. These experiments demonstrate that hypercapnic acidosis significantly decreases oxygen supply to resting skeletal muscle in the anesthetized cat, probably via neuroregulatory responses to CO2 which do not depend on changes in arterial [H+] in the tested pH range.

The effect of systemic acidosis on perfusion of replanted extremities

By measuring skin temperature and muscle pH of replanted rat legs, we found that uncorrected systemic acidosis had a detrimental effect on perfusion of the replanted extremity. Following administration of systemic sodium bicarbonate and correction of acidosis, muscle pH and skin temperature returned to normal with 60 minutes after revascularization. Metabolic acidosis following major extremity replantation and respiratory acidosis after prolonged anesthesia for digital replantation(s) must be corrected to ensure optimal perfusion of the distal capillary bed.

The problem of tissue oxygenation in diabetes mellitus. I. Its relation to the early functional changes in the microcirculation of diabetic subjects

The underlying cause leading to the reversible functional changes in the microcirculation of insulin-dependent diabetic subjects early during the disease prior to any clinical signs of retinopathy and nephropathy (functional microangiopathy) is discussed. It is suggested that the initial microvascular dilation observed in diabetics is due to an autoregulatory response to relative tissue hypoxia providing an increased tissue perfusion in order to improve tissue oxygen delivery. Supporting evidence for this suggestion is derived from the findings that diabetics simultaneously may show increased tissue oxygen consumption and decreased ability of the circulating blood to release oxygen to the tissues. The latter defect is likely to be caused by two interrelated factors: 1. an increased proportion of haemoglobin A1c with high oxygen affinity, and 2. difficulties of maintaining a sufficiently high concentration of plasma inorganic phosphate in order to provide an optimal 2,3-diphosphoglycerate (2,3-DPG) content in the erythrocytes. The basal oxygen demand of diabetics may fluctuate even within a few hours dependent upon the state of metabolic control and is increased at times of poor regulation. Hence, diabetics may suffer from innumerable cellular hypoxic injuries, which during the first years of the disease are counteracted in the microcirculation by an autoregulatory response. These microvascular reactions associated with increased plasma permeation may over the years be of major importance for the development of the degenerative microangiopathy in diabetes.

Inhibition of the vasodilator effect of hypercapnic acidosis by hypercalcemia in dogs and rats

The vasodilator effect of local hypercapnic acidosis, produced by intra-arterial infusion of an acid buffer solution consisting of a mixture of glycine and hydrochloric acid, in the perfused hind limb and in the perfused gastrocnemius muscle of anesthetized dogs was examined at normal plasma calcium concentration and during elevation of the plasma calcium concentration produced by intra-arterial infusion of calcium chloride. Hypercalcemia inhibited the vasodilator action of hypercapnic acidosis so that the effect was not apparent until venous blood pH decreased below 7. The dilator effect of local application of acidified Ringer's solution on arterioles of the cremaster muscle of the rat was also inhibited by elevation of the plasma calcium concentration induced by intravenous administration of calcium chloride. The available evidence suggests that this inhibition of the dilator effect of hypercapnic acidosis by calcium ions is related to competition between calcium and hydrogen ions for binding at one or more cellular sites such as the sarcolemma, the sarcoplasmic reticulum, or the contractile proteins of vascular smooth muscle.

Renal physiology in children

The human kidney may not reach functional maturity until the age of 18 months. In the preceding months there are limitations in response to such stresses as salt and water loading, acidosis and dehydration. It is seen that these limitations must not be taken out of context of the overall situation of health or disease and of actual solute load. Almost all drug dosages for children are calculated on the basis of body size, and it should be recalled that in the first months of life there exists relative renal insufficiency on the basis of body weight or surface area in comparison with older children and adults.

Precise physiologic data are necessary for completely successful management of the critically ill patient. It is seen from this review that not only are there gaps in our knowledge of developmental renal physiology, but also the process of development has introduced another variable into the evaluation of the individual patient.