The role of pH, PCO2, and bicarbonate in regulating rat diaphragm citrate content

Abstract

A B S T R A C T Intact rat diaphragms were exposed in vitro to varying CO2 tensions and bicarbonate concentrations, and the steady-state citrate content of diaphragm muscle was measured to investigate the relationship between metabolism and extracellular pH, Pco2, and (HC03-). In addition, rat hemidiaphragms were incubated with 1,5-citrate-1'C under different acid-base conditions, and "CO2 production was determined as a measure of citrate oxidation.Acidification of the bathing medium achieved by raising C02 tension or lowering (HCO3-) was associated with a decrease in muscle citrate content. On the other hand, alkalinization of the medium induced by lowering CO tension or raising (HCO3-) caused tissue citrate content to rise. At a physiologic extracellular pH value of approximately 7.40, citrate content was decreased or normal depending on the CO2/HC03-combination employed to attain the pH. Under low bicarbonate and low Pco2 conditions, citrate content was reduced. A similar result was found at external pH values of 7.15, implying that at these two extracellular pH levels (HCOa-) primarily determines citrate content. When changes in citrate content were compared with intracellular pH data reported earlier using the same intact diaphragm preparation, no simple relation between citrate content and intracellular pH was found. The effect of acidity on citrate content seems related to a change in citrate oxidation since the latter increased progressively with increasing degrees of medium acidity.These results show that cellular metabolism is not a simple function of extracellular pH but is dependent on the particular combination of Pco2 and bicarbonate employed to achieve the pH value. These studies also suggest that accumulation or disposal of organic acids, such as citric acid, helps to regulate cellular acidity thereby contributing to the cells' defense against external acid-base disorders.An (6)(7)(8)(9). Second, cell pH was found not to have a simple relationship to extracellular pH but appeared to be a complex function dependent on the particular combination of Pco2 and bicarbonate used to achieve a particular extracellular pH value (4). Third, the cell was able to maintain its pH constant over a wide range of extracellular acidity (3). Adler, Roy, and Relman speculated that this remarkable ability of the cell to maintain its pH constant could be due either to changes in the flux rates of hydrogen, hydroxyl, or bicarbonate ions or to changes in the internal metabolism of acids or bases (3).This study was undertaken to de~termine if the content of a key intermediary metabolite, citrate, varied in intact diaphragm when extracellular pH was systematically altered, and whether any changes found were due to extracellular pH alone or were dependent on the C02 tension or bicarbonate concentration of the extracellular fluid. Citrate was chosen since its metabolism has been shown to vary directly with pH in renal cortical slices (10). In addition, the citrate content of rat gluteal muscle changes markedly when an extra...

Intracellular Acid-Base Heterogeneity in Nucleated Avian Erythrocytes

“…The metabolism of liver tissue and skeletal muscle cells can be affected by proportionate changes in Pcoz and bicarbonate concentration, which do not alter [H+]. or mean cell [H+], measured by DMO (Longmore, Niethe & McDaniel, 1969;Adler, 1970;Adler, Anderson & Zett, 1972), and these results could be explained if [H+Ii(DMO) does not reflect changes in [H+] in the regions of the cell where the relevant enzymes are situated.…”

An Extrarenal Role for Parathyroid Hormone in the Disposal of Acute Acid Loads in Rats and Dogs

“…Intact rat diaphragmls wvere obtained from 75-to 90-g non-TPTX Sprague-Dawlev rats and incubated simultaneously in two boxes at 37°C in a modified Krebs-Ringer bicarbonate solution conitaininig 100 mg/100 ml of glucose and 6.25 mg/100 ml of chloromycetin as described (8). The solution was gassed with a 4.86% CO2 balance oxygen gas mixture.…”

“…During the final hour of incubation, 80 mg/100 ml of inulin was added to each bath to meassure extracellular space, and 25 ACi of [2-'4C]DMO was added to each solution for calculation of intracelltular pH. At the end of the experiment, diaphragmiis were removed alternately from the two boxes for cell pH determination (8). Bath pH was -7.00, achieved by using a bicarbonate concentration of 10 meq/liter.…”

Changes in bone sodium and carbonate in metabolic acidosis and alkalosis in the dog

“…DISCUSSION Although there has been considerable past interest in bone and acid-base metabolism, as described in the introduction, our interest was rekindled by failure to account for all of the acid balance changes by summation of changes in body fluids in studies in dogs (19,20). The implication was that either bone was more important than generally viewed, or that metabolic cellular events played an important role (16,21). Since it was postulated that analysis of the kinetics of cellular change argued against the importance of cellular metabolism (19), a direct reexamination of bone in adult animals was indicated.…”

“…This inability to account for all of the added acid or alkali can be explained by alteration in the cellular rate of metabolic acid production (16,21) or by the existence of changes in bone C03=. The present study was undertaken to test the hypothesis that plasma acidity is important in determination of bone C08= and that the magnitude of bone C03-change is adequate to explain the "unaccounted for" acid gain or loss obtained by summation of changes in extra-and intracellular body fluid compartments.…”