Effect of pH on the calcium metabolism of isolated rat kidney cells

Effects of pH on calcium transport in turtle bladder

This study was designed to examine the effect of apical and basolateral (ie, mucosal and serosal) pH on calcium (Ca) transport in turtle bladder, a nonmammalian analog of the distal nephron. Unidirectional Ca45 fluxes were measured when serosal pH was 6.4, 7.4, or 8.4 (mucosal pH, 7.4) in the presence and absence of ouabain. When serosal pH was 8.4, M-->S Ca45 flux increased significantly, and when it was 6.4, M-->S Ca45 flux decreased markedly. Changes in serosal pH did not affect the S-->M Ca45 flux. When 5 x 10(-4) mol/L ouabain was added to inhibit sodium transport, M-->S Ca45 flux, at pH 7.4, was 221.6 +/- 27.4 pmol/mg/h (n = 10), and low pH again inhibited this flux (approximately 50%). Lowering mucosal pH (with serosal pH 7.4) also decreased M-->S Ca45 flux. In stripped bladders, Ca45 uptake increased linearly as medium pH was increased from 4.4 to 8.4. Total tissue Ca concentration did not change when serosal pH was varied, except at the extreme of pH 4.4, where tissue Ca decreased. By contrast, when apical pH was 6.4, tissue Ca rose substantially (approximately 1.5-fold). these results demonstrate that extracellular pH directly affects Ca homeostasis in the turtle bladder. Lowering the pH of either the serosal or mucosal medium directly inhibits apical Ca permeability. This change in Ca permeability is seen in the presence of ouabain. By contrast, alkalization of the serosal medium enhances apical permeability, but this effect is, in some manner, related to sodium transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of high and low pH on Ca2+i and on cell injury evoked by anoxia in perfused rat hepatocytes

The effect of high and low pH on anoxic cell injury was studied in freshly isolated rat hepatocytes cast in agarose gel threads and perfused with Krebs-Henseleit bicarbonate buffer (KHB) saturated with 95% O2 and 5% CO2. Cytosolic free calcium (Ca2+i) was measured with aequorin, intracellular pH (pHi) with BCECF, and lactic dehydrogenase (LDH) by the increase in NADH absorbance during lactate oxidation to pyruvate. A 2 h period of anoxia was induced by perfusing the cells with KHB saturated with 95% N2 and 5% CO2. The extracellular pH (pHo) was maintained at 7.4, 6.8 or 8.0 by varying the bicarbonate concentration. The substrate was either 5 mM glucose, 15 mM glucose or 15 mM fructose. In some experiments, anoxia was performed in Ca(2+)-free media by perfusing the cells with KHB without Ca2+ but with 0.1 mM EGTA. Reducing pHo to 6.8 during anoxia did not reduce the increase in Ca2+i, but but completely abolished LDH release. Under these conditions, pHi decreased to 6.56 +/- 0.3 when glucose was the substrate and to 6.18 +/- 0.25 with 15 mM fructose. Apparently, protection against anoxic injury caused by a low pHo is associated with a low pHi but not with a reduced elevation in Ca2+i. Increasing pHo to 8.0 during anoxia increased pHi above 8.0 +/- 0.01 and doubled LDH release without significantly altering the rise in Ca2+i. When 15 mM fructose was present with a pHo of 8.0, pHi was still 8.0, but there was practically no rise in Ca2+i, and LDH release was again completely abolished. On the other hand, a Ca(2+)-free perfusate with a pHo of 8.0 kept the rise in Ca2+i below 400 nM but did not abolish the massive release of LDH caused by high pH. Since cell injury is caused by the activation of Ca(2+)-sensitive hydrolytic enzymes such as phospholipase A2, these experiments suggest that a low pH (< 6.5) prevents their activation even in the presence of a high Ca2+i. Conversely, a high pH (> 8.0) can activate hydrolytic enzymes and cause injury even in the absence of an elevated Ca2+i. The precise mechanism by which fructose protects hepatocytes against cell injury at pHi 8.0 is unclear.

Acute phosphate depletion and in vitro rat proximal tubule injury: protection by glycine and acidosis

The effects of phosphate (PO4) removal from Krebs Henseleit buffer on freshly isolated rat proximal tubules (rPT) were assessed by measuring Ca2+ uptake (nmol/mg protein), cellular adenosine triphosphate (ATP) (nmol/mg), tissue K+ content (nmol/mg) and lactate dehydrogenase (LDH) as an index of cell integrity. Ca2+ uptake increased by 50% in rPT incubated in zero PO4 medium as compared to control (2.6 +/- 0.1 vs. 3.9 +/- 0.19, P less than 0.001) and LDH release increased 2.5-fold from 14.2 +/- 0.6 to 31.6 +/- 1.6%, P less than 0.001. Neither verapamil (200 microM) nor mepacrine (50 microM) reduced Ca2+ uptake or decreased LDH release suggesting that the increased Ca2+ uptake was not occurring through potential operated channels and that phospholipase-induced cell injury was not the cause of increased LDH release. Either glycine (2 mM) or extracellular fluid acidosis (pH 7.06), however, significantly diminished rPT injury and Ca2+ uptake. Specifically, as compared to the increased LDH released in untreated. PO4-depleted rPT, LDH release was diminished significantly by glycine treatment (31.0 +/- 0.9 vs. 15.5 +/- 1.6%, P less than 0.001) or acidosis (30.3 +/- 0.04 vs. 19.2 +/- 0.9%, P less than 0.01). Ca2+ uptake did not increase in glycine treated tubules (2.6 +/- 0.1 vs. 2.8 +/- 0.2 nmol/mg, NS) or in the presence of acidosis (2.6 +/- 0.1 vs. 2.97 +/- 0.17 nmol/mg, NS). ATP concentrations were markedly reduced by PO4 depletion (2.8 +/- 0.2 vs. 4.8 +/- 0.3 nmol/mg, P less than 0.001) and remained at low levels during either acidosis or glycine-induced protection.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic respiratory acidosis on urinary calcium excretion in the dog

It is currently believed that the two chronic acidemic disorders exert disparate effects on urinary calcium excretion: chronic metabolic acidosis induces consistent hypercalciuria, but no appreciable change or even a decrease in calcium excretion is reported to attend chronic respiratory acidosis. Whereas the effect of metabolic acidosis is well documented, little work has been carried out in chronic hypercapnia. In fact, most of the studies on chronic respiratory acidosis were short in duration, had employed only mild hypercapnia, or had failed to control carefully the prevailing metabolic conditions. We have carried out balance observations in nine dogs exposed to a 10% CO2 atmosphere in an environmental chamber for a period of two weeks. Chronic respiratory acidosis led to a significant increase in urinary calcium excretion from a mean control value of 0.4 +/- 0.1 mmol/day to 0.6 +/- 0.1 mmol/day during both week 1 and 2 of hypercapnia (P less than 0.05). Hypercalciuria occurred even though filtered load of calcium fell. Mean fractional excretion of calcium increased significantly during each week of hypercapnia averaging 0.60 +/- 0.12% during control, 1.05 +/- 0.13% during week 1, and 1.26 +/- 0.17% during week 2 of hypercapnic exposure (P less than 0.05). There were no changes in plasma levels of immunoreactive parathyroid hormone or 1,25-dihydroxyvitamin D3. These findings suggest that chronic respiratory acidosis, just like chronic metabolic acidosis, augments urinary calcium excretion by a direct depressive effect on the tubular reabsorption of calcium.

Adenine nucleotides, transport activity and hypoxic necrosis in the thick ascending limb of Henle

Thick ascending limb of Henle (TAL) necrosis in the isolated perfused kidney is an important model of renal hypoxia, but physiologic and metabolic correlation with this morphologic damage has been inadequate. More precise estimation of TAL adenine nucleotides in this model was obtained in the present study by high pressure liquid chromatography analysis of biopsy samples from the inner stripe of the outer medulla during perfusion. The inner stripe, which is the zone where TAL are concentrated, showed ATP depletion and low adenylate energy charge (AEC) early in perfusion prior to the appearance of TAL necrosis. Free water clearance (CH2O) was used as an estimate of TAL transport activity; the CH2O observed during 90 minute perfusions was found to be predictive of the extent of TAL necrosis in each experiment. The results support the idea that there is significant medullary hypoxia in the isolated perfused kidney and that TAL solute transport is a determinant of injury in this model. In further studies, the effects of ouabain (10(-3) M), furosemide (10(-4) M) or acidosis (pH 7.0 rather than the usual pH 7.4) on TAL transport activity and adenine nucleotide levels were compared. All three maneuvers have been shown previously to reduce TAL injury in the isolated perfused kidney. Addition of ouabain or furosemide reduced CH2O and TAL necrosis in parallel while acidosis had no effect on CH2O during perfusion. Both ouabain and furosemide attenuated ATP depletion and resulted in higher AEC while acidosis had no effect on these indices of cellular hypoxia. Therefore, the mechanism of cytoprotection by acidosis appears distinct from that of ouabain or furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis and hypoxic medullary injury in the isolated perfused kidney

The effects of acidosis on renal function and morphology were examined in the isolated perfused rat kidney (IPK). Kidneys were perfused with oxygenated Krebs-Henseleit-albumin medium for 60 minutes at pH 7.4 or pH 7.0. At the lower pH, GFR was reduced by 25%, TRNa by 32% and oxygen consumption by 41% as compared to perfusion at pH 7.4 (all P less than 0.05). In addition, the usual hypoxic injury observed in the medullary thick ascending limb of the Loop of Henle (TAL) in the IPK at pH 7.4 (consisting of nuclear pyknosis and focal fragmentation necrosis) was reduced by acidosis from 62% to 14% of tubules involved (P less than 0.005). This cytoprotection was not the result of improved oxygenation since O2 delivery was actually slighty reduced at pH 7.0 compared to pH 7.4. Furthermore, acidosis was protective even after perfusion with non-oxygenated media (42% tubules damaged at pH 7.0 vs. 95% of tubules damaged at pH 7.4; P less than 0.01), making it very unlikely that the effect of acidosis is to improve TAL oxygenation. Since previous studies indicate that the TAL lesion is transport dependent and prevented in the non-filtering kidney, it was possible that the decrease in GFR associated with acidosis could account for decreased injury. The GFR was manipulated by alterations in perfusion pressure or albumin concentration, and no consistent relationship between the extent of injury and GFR could be shown at either pH over a wide range of GFR values. Therefore, acidosis protected the TAL from hypoxic injury by a mechanism apparently independent of oxygen or solute delivery.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of intracellular Ca2+ and elevation of inositol trisphosphate by secretagogues in parietal and chief cells isolated from rabbit gastric mucosa

The fluorescent intracellular Ca2+ indicator, fura2/AM, was used to determine the effects of carbachol, cholecystokinin octapeptide (CCK-8), gastrin and histamine on intracellular Ca2+ ([Ca2+]i) in parietal cells from rabbit gastric mucosa enriched to more than 95% purity by a new Nycodenz gradient/centrifugal elutriation technique. Changes in [Ca2+]i in response to the same agonists were also measured in enriched chief cells. Carbachol, histamine, gastrin and CCK-8 increased parietal cell [Ca2+]i with the response to carbachol greater than CCK -8 = histamine = gastrin. Prestimulation with msximal doses of carbachol blocked histamine-induced increases in [Ca2+]i. In chief cells, carbachol increased [Ca2+]i but to a lesser degree than CCK-8, while histamine had no significant effect on [Ca2+]i. Neither removal of extracellular Ca2+ coupled with acute addition of 1 mM EGTA nor addition of the Ca2+-channel blocker nicardipine prevented agonist-induced changes in [Ca2+]i in either cell type. In the presence and absence of 10 mM LiCl2, carbachol and CCK-8 were found to increase inositol trisphosphate (IP3) content in both parietal and chief cells while histamine had no significant effect on this phosphoinositide hydrolysis product. From these results and previous observations with gastric glands (Chew, C.S. (1986) Am. J. Physiol. 13, G814-G823) we conclude that: carbachol, CCK-8, gastrin and histamine increase parietal cell [Ca2+]i initially by release of Ca2+ from the same intracellular store(s); the release of [Ca2+]i in response to carbachol and CCK-8 in both chief and parietal cells appear to be mediated by IP3; however, other mechanisms may be involved in histamine-induced release of parietal cell Ca2+.

Effects of metabolic acidosis on viability of cells exposed to anoxia

The effects of metabolic acidosis were examined in isolated rat hepatocytes under substrate-free oxygenated or anoxic conditions. Lowering extracellular pH to 6.6 under aerobic conditions had no deleterious effects on the cells as determined by trypan blue exclusion, lactate dehydrogenase (LDH) release, cellular K+ and Ca2+ content, and ability to increase ATP levels after nutrients and adenosine were added to media. Cytosolic pH was measured in aerobic cells at varying extracellular pH using 6-carboxyfluorescein. By using values for cytosolic pH obtained in this manner together with 5,5-dimethyl[2-14C]oxazolidine-2,4-dione (DMO) distribution data, a method was derived for determining intramitochondrial pH. The pH gradient across the mitochondrial membrane was found not to change with a decrease in extracellular pH from 7.4 to 6.9. At pH 6.9 hepatocytes were protected against anoxic injury as compared with cells incubated at pH 7.5 or 6.6. This protection was manifested by a decrease in vital dye uptake and LDH release, maintenance of higher cellular K+ content, less stimulation of respiration with succinate, improved recovery of ATP levels after return to an oxygenated nutrient environment, and maintenance of normal cellular Ca2+ content after reoxygenation. Recovery of cellular ATP content was independent of ATP levels, total adenine nucleotide pool, and energy charge ratio at the end of the anoxic period. Measurement of cytoplasmic pH in anaerobic cells by [14C]DMO distribution showed progressive cellular acidification with lowering of extracellular pH. The protective effects observed at pH 6.9 are not unique to hepatocytes since isolated renal cortical tubules exposed to anoxia have improved ATP levels on reoxygenation at this pH when compared with tubules incubated at pH 7.5.

Effect of calcium ionophore A23187 on electrogenic acid-base transport in turtle bladder. Inhibition of acidification and stimulation of alkalinization

Turtle bladders bathed on both surfaces with identical HCO3-/CO2-rich, Cl--free Na+ media and treated with ouabain and amiloride exhibit a transepithelial potential serosa electronegative to mucosa and a short-circuit current (Isc) which is a measure of the net luminal acidification rate. Addition of calcium ionophore A23187 (10 microM) to the mucosal side of the epithelium rapidly reverses the direction of the potential difference and Isc and decreases tissue resistance. The resulting positive Isc resembles that previously observed in response to isobutylmethylxanthine (IBMX) and cAMP analogs. Reversal of the Isc is enhanced in bladders from severely alkalotic turtles. In contrast, in severely acidotic turtles, ionophore A23187 decreases, but does not reverse, the Isc. The data suggest that, like IBMX and cAMP analogs, the Ca ionophore stimulates an electrogenic alkalinization mechanism, but, unlike the former agents, inhibits the concurrent acidification process as well.

Active electrogenic mechanisms for alkali and acid transport in turtle bladders

Immediately after mounting in the Ussing chamber between choline bicarbonate Ringer solutions devoid of exogenous Na and Cl, the serosal fluid is electronegative to the luminal fluid in bladders from postabsorptive and acidotic turtles; and electropositive in bladders from alkalotic turtles. In bladders from postprandial turtles, the electrical orientation, initially serosal positive, reverses to serosal negative. Serosal additions of 3-isobutyl-1-methylxanthine (IBMX) and adenosine 3',5'-cyclic monophosphate (cAMP) produce no changes in the negative short-circuiting current (Isc) of acidotic turtles but induce large positively-directed increases of Isc in bladders from other turtle groups. With IBMX and cAMP in the (HCO3 + CO2)-rich serosal fluid at pH 7.2 and with luminal pH maintained at 4.0-5.0, the rate at which titratable alkali enters the luminal fluid is electrochemically equal to the positive Isc; and this increased positive Isc is the same as that in the absence of transepithelial gradients. The effects of acetazolamide and 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonic acid on positive and negative Isc are presented. It is concluded that isolated bladders from alkalotic, postprandial or postabsorptive turtles, but not those from acidotic turtles, possess an active electrogenic mechanism for a Na-independent Cl-independent secretion of bicarbonate. This transport process is accelerated by phosphodiesterase inhibitors (IBMX) and cAMP or its eight substituted derivatives.

Computer simulation and interpretation of 45Ca efflux profile patterns

Stimulations or inhibitions by various agents of 45Ca efflux from prelabeled cells or tissues display distinct and reproducible profile patterns when the results are plotted against time as fractional efflux ratios (FER). FER is the fractional efflux of 45Ca from stimulated cells divided by the fractional efflux from a control unstimulated group. These profile patterns fall into three categories: peak patterns, exponential patterns, and mixed patterns. Each category can be positive (stimulation) or negative (inhibition). The interpretation of these profiles is difficult because 45Ca efflux depends on three variables: the rate of calcium transport out of the cell, the specific activity of the cell compartment from which the calcium originates, and the concentration of free calcium in this compartment. A computer model based on data obtained by kinetic analyses of 45Ca desaturation curves and consisting of two distinct intracellular pools was designed to follow the concentration of the traced substance (40Ca), the tracer (45Ca), and the specific activity of each compartment before, during, and after the stimulation or the inhibition of calcium fluxes at various pool boundaries. The computer model can reproduce all the FER profiles obtained experimentally and bring information which may be helpful to the interpretation of this type of data. Some predictions of the model were tested experimentally, and the results support the views that a peak pattern may reflect a sustained change in calcium transport across the plasma membrane, that an exponential pattern arises from calcium mobilization from an internal subcellular pool, and that a mixed pattern may be caused by a simultaneous change in calcium fluxes at both compartment boundaries.

Effect of sodium on cellular calcium transport in rat kidney

The influence of extracellular Na (Na0) on cellular Ca transport and distribution was studied in rat kidney slices. Calcium efflux from prelabeled slices was depressed when Na0 was completely replaced by choline or tetraethylammonium (TEA) ions and it was markedly stimulated when Na was reintroduced in a Na-free medium. However, reducing Na0 (with choline or TEA as substituting ions) did not increase the total slice 40Ca, their total exchangeable Ca pool, or the 40Ca or 45Ca of mitochondria isolated from these slices. Kinetic analyses of steady-state 45Ca desaturation curves showed that reducing Na0 depressed the exchange of Ca across the plasma membrane, slightly decreased the cytosolic Ca pool, but did not significantly affect the mitochondrial Ca pool and Ca cycling. Ouabain (10(-3)M) which should reduce the Na gradient across the plasma membrane had no effect on calcium distribution and transport. These results suggest that in kidney cells low Na0 depresses Ca influx as well as Ca efflux; there may be an interaction between Na and Ca at a possible carrier located in the plasma membrane, but there is no Na/Ca exchange as described in several excitable tissues.

Inhibition of 25-hydroxyvitamin D3-1-hydroxylase by chronic metabolic acidosis

Chronic metabolic acidosis had been shown to influence the renal metabolism of 25-hydroxyvitamin D3. Using the isolated perfused rat kidney model, we evaluated the rates of synthesis of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in vitamin D-depleted [D(-)] and 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] in vitamin D-replete [D(+)] rats. Metabolic acidosis was induced in both groups of rats by feeding aqueous ammonium chloride for 9 days. Kidneys isolated from D(-) acidotic rats (mean pH, 7.11) exhibited a decreased rate of 1,25(OH)2D3 synthesis (0.79 +/- 0.17 pmol produce . h-1 . g kidney-1) when compared with that (1.27 +/- 0.09) of D(-) nonacidotic (mean pH, 7.33) rats. There was a significant negative linear correlation between the rate of synthesis of 1,25(OH)2D3 and the hydrogen ion concentration of the animal (r = 0.79, P less than 0.005). The rate of synthesis of 24,25(OH)2D3 by the kidneys from D(+) acidotic (mean pH, 7.06) and nonacidotic (mean pH, 7.39) rats did not differ (0.81 +/- 0.21 vs. 0.60 +/- 0.12 pmol product . h-1 . g kidney-1). It is concluded that chronic acidosis suppressed 1-hydroxylase activity, but does not suppress 24-hydroxylase activity.

Response of isolated rat heart cells to hypoxia, re-oxygenation, and acidosis

Responses of isolated adult rat heart cells to conditions that emphasize various aspects of ischemia have been evaluated. Cells maintained in hypoxic media with limited substrate deteriorate more rapidly than aerobic controls supplemented with glucose. Two distinct irreversible pathways for cell alteration can be distinguished as follows: (1) continued anaerobic aging in the absence of glucose results in the production of large numbers of cells which retain the rod-shaped morphology of heart cells in situ, but which have lost sarcolemmal integrity, and (2) after a period of anaerobic aging, reaeration of the cells produces large numbers of rounded cells in irreversible contracture. These cells maintain an intact sarcolemma and are indistinguishable from those produced by addition of 1 mM Ca2+ to Na+-loaded, aerobic cells. Contracture of isolated cells on re-aeration is at least superficially analogous to the oxygen paradox in situ, but since the isolated cells maintain an intact sarcolemma, there is no loss of creatine phosphokinase or other components of the cytosol. Incubation of isolated heart cells at acid pH (pH 6.8 to 6.2) largely prevents both Ca2+-dependent contracture and a Ca2+- dependent loss of respiratory capacity. The acidic conditions virtually eliminate the net influx of 45Ca2+ into isolated cells that occurs at neutral pH, and the inhibition appears to be localized at the sarcolemma.

A kinetic analysis of the effects of adrenaline on calcium distribution in isolated rat liver parenchymal cells

1. The effects of adrenaline on Ca distribution in isolated rat liver parenchymal cells were studied using a (45)Ca exchange technique under steady-state conditions with respect to the net movement of Ca. (45)Ca was initially introduced into the extracellular medium. The amount of cellular (45)Ca was determined after separation of the cells from the medium by centrifugation through a solution which contained LaCl(3) (to displace (45)Ca bound to sites on the outside of the cell membrane) and silicon oil. At 1.3 and 2.4 mm-extracellular Ca, a stimulation of the initial rate of (45)Ca exchange was observed in the presence of 10(-7)m-adrenaline (or 10(-6)m-phenylephrine) with a 7% decrease, and no change, respectively, in the plateau of the exchange curve. The same degree of stimulation was observed when (45)Ca was added at 1, 15, 30 or 45 min after the adrenaline.2. No stimulation of the initial rate of exchange was observed at 0.1 mm-extracellular Ca, or at 2.4 mm-extracellular Ca in the presence of antimycin A and oligomycin. At 0.1 mm-Ca, a 60% decrease in the plateau of the exchange curve was observed in the presence of adrenaline. The concentration of adrenaline (10(-7)m) which caused half-maximal stimulation of the initial rate of (45)Ca exchange at 1.3 mm-Ca was similar to that (2 x 10(-7)m) which caused half-maximal decrease in the plateau at 0.1 mm-Ca.3. The addition of adrenaline to cells equilibrated with (45)Ca at either 2.4 or 1.3 mm-Ca caused a transient loss of (45)Ca followed by a return to a new steady state after 1 or 10 min, respectively. A loss of (45)Ca was also observed at 0.1 mm-Ca, but the (45)Ca content of the cells remained maximally depressed for at least 30 min.4. A non-linear least-squares iterative curve-fitting technique was used to demonstrate that (a) an equation which includes two exponential terms and (b) a parallel or series arrangement of three compartments of exchangeable Ca (the medium and two compartments associated with the cell) are consistent with each set of data obtained at 1.3 or 2.4 mm-Ca in the presence or absence of adrenaline (or phenylephrine). At 1.3 mm-Ca, the quantities of exchangeable Ca in the two kinetically defined cellular compartments were 0.04-0.07 and 0.34-0.37 nmol per mg wet weight with rate constants for Ca outflow of 1.2-1.5 and 0.06-0.08 min(-1), respectively.5. Analysis of the changes induced by adrenaline or phenylephrine showed that at 1.3 and 2.4 mm-extracellular Ca these agents caused a 75-150% increase in the quantity of exchangeable Ca in the small kinetically defined compartment and a 20% decrease in the quantity of exchangeable Ca in the large kinetically defined compartment. These changes were mediated by an 80-160% increase in the rate constant for the inflow of Ca from the medium to the small kinetically defined compartment, and either a 20-60% decrease in the rate constant for inflow to, or a 20% increase in the rate constant for outflow from, the large compartment.6. Replacement of the LaCl(3) in the solution used to separate the cells from the incubation medium with either 5 mm-EGTA or 5 mm-CaCl(2) did not alter the kinetics of (45)Ca exchange or the stimulation by adrenaline. This, together with the observation that at 1.3 mm-extracellular Ca, adrenaline increases the initial rate of exchange in the absence, but not in the presence, of antimycin A plus oligomycin, indicates that both cellular compartments of exchangeable Ca are intracellular.7. The addition of antimycin A plus oligomycin to cells equilibrated with (45)Ca at 2.4 mm-extracellular Ca in the presence or absence of adrenaline displaced 0.09 and 0.14 nmol (45)Ca. mg(-1), respectively.8. Subcellular fractionation of cells equilibrated with (45)Ca at 0.1 mm-extracellular Ca revealed that the mitochondria and microsomes contained significant amounts of (45)Ca. The amounts of (45)Ca in these fractions decreased by 50 and 40%, respectively, in the presence of adrenaline.9. In (45)Ca exchange experiments conducted with isolated mitochondria at 37 degrees C at 1.5 x 10(-7)m and 0.9 x 10(-7)m free Ca in the presence of 2 mm-Mg(2+), one kinetically defined compartment of exchangeable mitochondrial Ca was detected. The rate constants for Ca outflow were found to be 0.15+/-0.03 and 0.12+/-0.04 min(-1), respectively, in reasonable agreement with the value obtained for the rate constant for the outflow of Ca from the large kinetically defined compartment of exchangeable Ca observed in cells.10. It is concluded that adrenaline has two effects on Ca movement in the liver cell. These are to cause a loss of Ca from an intracellular compartment, which includes the mitochondria and microsomes, and to increase the transport of Ca from the extracellular medium to an intracellular site. This results in an increase in the amount of Ca in a small intracellular compartment which may represent cytoplasmic Ca, or Ca bound to sites on the inside of the plasma membrane.

The role of intrarenal pH in regulation of ammoniagenesis: [31P]NMR studies of the isolated perfused rat kidney

1. [31P]NMR spectra were obtained from a functioning isolated perfused rat kidney with the aim of determining intrarenal pH in acute acidosis. 2. Signals from intracellular inorganic phosphate could be observed in the absence of phosphate in the perfusion medium. Under these conditions renal ATP and inorganic phosphate content fell by 30% but total adenine nucleotide and phosphorylation potential ATP/ADP x Pi were unchanged compared with kidneys perfused with phosphate-containing medium. In addition, G.F.R., Na+ reabsorption and ammonia formation from glutamine remained normal. Ammonia production increased 93%, urine pH fell to 5.8 +/- 0.1 and kidney 2-oxoglutarate content fell by 80% upon acidification of the perfusion medium from pH 7.4 to pH 6.9, findings identical with those obtained in controls (Ross & Tannen, 1979). 3. [31P]NMR spectra of the isolated perfused rat kidney showed a pattern of adenine nucleotides and a small concentration of phosphocreatine, Intra-renal pH was measured from the resonance position of intracellular inorganic phosphate and in perfusions with pH 7.4 buffer was 7.19 +/- 0.10 (n = 11). 4. Acidification of the perfusion medium to pH 7.0 resulted in 0.3 pH unit fall in intrarenal pH. This fall in total intrarenal pH is insufficient to explain the fall in 2-oxoglutarate concentration observed if the glutamate-dehydrogenase-equilibrium model is invoked. 5. The line-width of the NMR signal is compatible either with heterogeneity of intra-renal pH or the existence of a pH gradient between cytosol and mitochondria, or both.