Systemic acidemia impairs cardiac function in critically Ill patients.

BACKGROUND: Acidemia, is associated with reduced cardiac function in animals, but no studies showing an effect of acidemia on cardiac function in humans are reported. In the present study, we examined the effect of acidemia on cardiac function assessed with transpulmonary thermodilution technique with integrated pulse contour analysis (Pulse Contour Cardiac Output, PiCCO™) in a large cohort of critically ill patients. METHODS: This was a prospective multicenter observational cross-sectional study of 297 patients from 6 intensive care units in London, England selected from all patients admitted consecutively between May 2018 and March 2019. Measurements of lowest plasma pH and concurrent assessment of cardiac function were obtained. FINDINGS: There was a significant difference between two pH categories (pH ≤ 7.28 vs. pH > 7.28) for the following variables of cardiac function: SVI (difference in means 32.7; 95% CI: 21 to 45 mL/m2; p < 0.001); GEF (18; 95% CI: 11 to 26%; p < 0.001), dPmax (-331; 95% CI: -510 to -153 mmHg/s; p = 0.001), CFI (0.7; 95% CI: 0.2 to 1.3 1/min; p = 0.01) and CPI (0.09; 95% CI: 0.03 to 0.15 W/m2; p < 0.001). However, there was no significant difference in CI (0.13; 95% CI: -0.20 to 0.47 L/min/m2; p = 0.12) between the pH categories. Also, a significant relationship was found between the quantitative pH and the following variables: SVI (132; 95% CI: 77 to 188 mL/m2; p < 0.001), GEF (74.7; 95% CI: 37.1 to 112.4%; p < 0.001), dPmax (-1587; 95% CI: -2361 to -815 mmHg/s; p < 0.001), CFI (3.5; 95% CI: 0.9 to 6.1 /min; p = 0.009), CPI (0.62; 95% CI: 0.36 to 0.88 W/m2; p < 0.001) and CI (regression coefficient 1.96; 95% CI:0.45 to 3.47 L/min/m2; p = 0.01). INTERPRETATION: Acidemia is associated with impaired cardiac function in seriously ill patients hospitalized in the intensive care unit supporting the potential value of early diagnosis and improvement of arterial pH in these patients. FUNDING: The study was partially supported by unrestricted funds from the UCLA School of Medicine.

Urea transport in bacteria: acid acclimation by gastric Helicobacter spp.

Urea transporters in bacteria are relatively rare. There are three classes, the ABC transporters such as those expressed by cyanobacteria and Corynebacterium glutamicum, the Yut protein expressed by Yersinia spp and the UreI expressed by gastric Helicobacter spp. This review focuses largely on the UreI proton-gated channel that is part of the acid acclimation mechanism essential for gastric colonization by the latter. UreI is a six-transmembrane polytopic integral membrane protein, N and C termini periplasmic, and is expressed in all gastric Helicobacter spp that have been studied but also in Helicobacter hepaticus and Streptococcus salivarius. The first two are proton-gated, the latter is pH insensitive. Site-directed mutagenesis and chimeric constructs have identified histidines and dicarboxylic amino acids in the second periplasmic loop of H. pylori and the first loop of H. hepaticus UreI and the C terminus of both as involved in a hydrogen-bonding dependence of proton gating, with the membrane domain in these but not in the UreI of S. salivarius responding to the periplasmic conformational changes. UreI and urease are essential for gastric colonization and urease associates with UreI during acid exposure, facilitating activation of the UreA and UreB apoenzyme complex by Ni2+ insertion by the UreF-UreH and UreE-UreG assembly proteins. Transcriptome analysis of acid responses of H. pylori also identified a cytoplasmic and periplasmic carbonic anhydrase as responding specifically to changes in periplasmic pH and these have been shown to be essential also for acid acclimation. The finding also of upregulation of the two-component histidine kinase HP0165 and its response element HP0166, illustrates the complexity of the acid acclimation processes involved in gastric colonization by this pathogen.

Detection and localization of H+-K+-ATPase isoforms in human kidney.

An H+-K+-ATPase contributes to hydrogen secretion and potassium reabsorption by the rat and rabbit collecting ducts. Transport of these ions appears to be accomplished by one or both of two isoforms of the H+-K+-ATPase, HKalpha(1) and HKalpha(2,) because both isoforms are found in the collecting ducts and transport of hydrogen and potassium is attenuated by exposure to inhibitors of these transport proteins. To evaluate whether an H+-K+-ATPase is present in the human kidney, immunohistochemical studies were performed using normal human renal tissue probed with antibodies directed against epitopes of three of the known isoforms of the H+-K+-ATPase , HKalpha(1), HKalpha(2), and HKalpha(4), and the V-type H+-ATPase. Cortical and medullary tissue probed with antibodies against HKalpha(1) showed cytoplasmic staining of intercalated cells that was less intense than that observed in the parietal cells of normal rat stomach stained with the same antibody. Also, weak immunoreactivity was detected in principal cells of the human collecting ducts. Cortical and medullary tissue probed with antibodies directed against HKalpha(4) revealed weak, diffuse staining of intercalated cells of the collecting ducts and occasional light staining of principal cells. Cortical and medullary tissue probed with antibodies directed against the H+-ATPase revealed staining of intercalated cells of the collecting ducts and some cells of the proximal convoluted tubules. By contrast, no discernible staining was noted with the use of the antibody against HKalpha(2). These data indicate that HKalpha(1) and HKalpha(4) are present in the collecting ducts of the human kidney. In this location, these isoforms might contribute to hydrogen and potassium transport by the kidney.

Use of base in the treatment of severe acidemic states.

Severe acidemia (blood pH < 7.1 to 7.2) suppresses myocardial contractility, predisposes to cardiac arrhythmias, causes venoconstriction, and can decrease total peripheral vascular resistance and blood pressure, reduce hepatic blood flow, and impair oxygen delivery. These alterations in organ function can contribute to increased morbidity and mortality. Although it seemed logical to administer sodium bicarbonate to attenuate acidemia and therefore lessen the impact on cardiac function, the routine use of bicarbonate in the treatment of the most common causes of severe acidemia, diabetic ketoacidosis, lactic acidosis, and cardiac arrest, has been an issue of great controversy. Studies of animals and patients with these disorders have reported conflicting data on the benefits of bicarbonate, showing both beneficial and detrimental effects. Alternative alkalinizing agents, tris-hydroxymethyl aminomethane and Carbicarb, have shown some promise in studies of animals and humans, and reevaluation of these buffers in the treatment of severe acidemic states seems warranted. The potential value of base therapy in the treatment of severe acidemia remains an important issue, and further studies are required to determine which patients should be administered base therapy and what base should be used.

HEMO equilibrated Kt/V goals are difficult to achieve in large male patients.

The long-term outcome of chronic hemodialysis patients is influenced by the adequacy of dialysis treatment. A major objective of the ongoing US HEMO Study is to determine if a higher target value of treatment as measured by the equilibrated Kt/V (eKt/V), a calculation of dialysis adequacy developed for the study, of 1.45 results in a better outcome than the presently accepted target value for eKt/V of 1.05 (approximately equal to spKt/V of 1.2). eKt/V corrects for urea rebound and gives a better estimate of actual treatment received. To examine the feasibility of achieving the higher eKt/V in large hemodialysis patients, a retrospective analysis of 389 monthly eKt/V values from 65 men on chronic hemodialysis of larger than average size dialyzed at high blood and dialysate flows (QB 400, QD 800 ml/min) with large dialyzers (1.8-2.2 m2) for longer than 4 hours three times weekly was performed. A total of 278 treatments considered optimal by a blood water urea clearance estimate were included in the final analyses. The mean body weight and Chertow water volume were 84.3+/-16.5 kgm and 50.0+/-6.7 L, respectively. The mean sp Kt/V was 1.29+/-0.17. The mean eKt/V was 1.16+/-0.14 and was inversely correlated with weight and water volume (p < 0.0001). Despite the large dialyzers and high blood and dialysate flow rates, no patient weighing more than 80 kgm or with body water volume exceeding 46 liters achieved an eKt/V of 1.45. This study suggests that creative dialyses will be required to achieve the HEMO "high arm" target in large patients.

Approach to patients with acid-base disorders.

Disorders of acid-base balance are commonly encountered in clinical practice and can have a substantial impact on the prognosis of the patient. Moreover, identification of a particular acid-base disturbance can provide a clue to an underlying disorder. Proper evaluation and treatment of acid-base disorders requires a systematic and analytic approach including: (1) assess the accuracy of the acid-base values using the Henderson equation or Henderson-Hasselbalch equation, (2) obtain a complete history and physical examination, (3) calculate the serum anion gap, (4) identify the primary acid-base disturbance and determine whether a simple or mixed disturbance is present, (5) examine serum electrolytes and additional laboratory data, and (6) measure urine pH and urine electrolytes and calculate the urine anion and osmolal gaps. Strict adherence to these principles will enable the clinician to diagnose the acid-base disturbance in the majority of cases. To illustrate these principles, 5 cases of patients with acid-base disturbances are analyzed.

Disturbances of acid-base balance and bone disease in end-stage renal disease.

Bone disease in patients with chronic renal failure (CRF) is thought to be the consequence primarily of the interplay of several factors, including the serum levels of parathyroid hormone (PTH), vitamin D, calcium, and phosphorus, and exposure to bone toxins such as aluminum or amyloid. Recently the metabolic acidosis noted with CRF has been implicated as an additional factor contributing to the genesis of bone disease. Although metabolic acidosis might be the dominant factor in the cause of bone disease in some instances, more commonly this acid-base disturbance interacts with other factors contributing to the development of bone disease. The following article summarizes the data in support of an important role for metabolic acidosis in the genesis of bone disease in patients with CRF and presents our recommendations for treatment of uremic acidosis to prevent or treat the bone disease.

The Na(+)-K(+)-ATPase beta 1 subunit is associated with the HK alpha 2 protein in the rat kidney.

The Na-K-ATPase beta 1 subunit acts as the beta subunit for the HK alpha 2 protein in the rat kidney. The colonic H(+)-K(+)-ATPase is a member of the P-type ATPases, and has been shown to contribute to potassium transport by the mammalian kidney and colon. The P-type ATPases often consist of an alpha subunit that contains the catalytic site and a beta subunit that participates in regulation of enzyme activity and targeting of the enzyme to the plasma membrane. The cDNA of the alpha subunit (HK alpha 2) has been cloned and the HK alpha 2 protein has been isolated from the rat kidney and colon. However, a unique beta subunit for the colonic H(+)-K(+)-ATPase has not been described. To determine if one of the known beta subunits present in the kidney might act as the beta subunit for the colonic H(+)-K(+)-ATPase, microsomes enriched in the colonic H(+)-K(+)-ATPase were isolated using an HK alpha 2-specific antibody (AS 31.7) and the Minimac magnetic separation system. Immunoblots of rat kidney microsomal protein isolated with antibody AS 31.7 were probed with antibodies directed against the gastric HK beta subunit, Na(+)-K(+)-ATPase alpha 1, and Na(+)-K(+)-ATPase beta 1 subunits. A band of the appropriate size was detected with Na(+)-K(+)-ATPase beta 1-specific antibodies, but not those directed against HK beta 1. These data suggest that Na(+)-K(+)-ATPase beta 1 could be the beta subunit for the colonic H(+)-K(+)-ATPase in the kidney.

Effect of hypokalemia on the abundance of HK alpha 1 and HK alpha 2 protein in the rat kidney.

An H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase) contributes to potassium reabsorption by the collecting ducts of the rat kidney. mRNAs for two isoforms of the H(+)-K(+)-ATPase, HK alpha 1 and HK alpha 2, have been found in the rat kidney. To evaluate whether the HK alpha 1 and HK alpha 2 proteins are present in the rat kidney, microsomes enriched in HK alpha 1 or HK alpha 2 were isolated using the MiniMac magnetic separation system with antibodies directed against either HK alpha 1 (HK 12.18) or HK alpha 2 (AS 31.7). Immunoblots of rat kidney microsomal protein isolated with HK 12.18 revealed a band approximately 94 kDa in size that comigrated with the G1 fraction of the stomach. Immunoblots of rat kidney microsomal protein isolated with AS 31.7 revealed a band slightly greater than 94 kDa that comigrated with a band obtained from rat colonic microsomal protein. To examine the effect of perturbations in potassium metabolism, the abundance of the HK alpha 1 and HK alpha 2 isoforms was compared in rats fed a normal or potassium-deficient diet. A low-potassium diet increased the abundance of HK alpha 2, whereas that of HK alpha 1 was not altered. These data suggest that HK alpha 2 might be the isoform responsible for potassium conservation by the kidney.

Effect of chronic respiratory acidosis on calcium metabolism in the rat.

Chronic metabolic acidosis typically results in hypercalciuria and negative calcium balance. The impact of chronic respiratory acidosis on calcium metabolism has been less well studied. To address this issue, metabolic balance and static bone histomorphometric data were obtained during a 14-day exposure of rats to 10% CO2 (blood pH 7.33, PaCO2 83 mm Hg) and were compared with pair-fed controls. All rats were fed a 0.8% calcium diet. Urinary calcium excretion (mg/period, mean +/- SEM) was increased during both week 1 and week 2 (16 +/- 3 vs 9 +/- 1 and 16 +/- 2 vs 9 +/- 1, CO2 group vs controls, respectively [p < 0.05]). Net intestinal calcium absorption (intake minus fecal excretion) was increased throughout the period of hypercapnia (week 1, 213 +/- 19 mg vs 135 +/- 15 mg; week 2, 135 +/- 16 mg vs 43 +/- 14 mg; and cumulatively, 344 +/- 27 mg vs 178 +/- 20 mg, CO2 group vs controls [p < 0.01]). As a consequence of the marked increment in intestinal calcium absorption during hypercapnia, mean net calcium balance was more positive than that of controls throughout the study (week 1, 197 +/- 18 mg vs 126 +/- 15 mg; week 2, 120 +/- 15 mg vs 34 +/- 15 mg; and cumulatively, 317 +/- 25 mg vs 159 +/- 20 mg, CO2 group vs controls, respectively [p < 0.01]). There were no significant differences in calcium intake, plasma total calcium, immunoreactive parathyroid hormone, 25-hydroxyvitamin D, or creatinine clearance between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of gastric and colonic H(+)-K(+)-ATPase in the rat kidney.

Enzymatic and microperfusion studies have indicated that an ATP-dependent H+/K+ exchange process is present in the collecting duct of the mammalian kidney. Immunochemical staining has also provided evidence for expression of a gastric-type H(+)-K+ adenosine triphosphatase (H(+)-K(+)-ATPase). Rat kidney mRNA was probed with use of the polymerase chain reaction (PCR) to determine the presence of an H(+)-K(+)-ATPase. cDNA made with mRNA isolated from the kidneys of rats maintained on a low-K diet was used as template in PCR reactions with primers encompassing the cDNA sequence of the alpha-subunit of the gastric H(+)-K(+)-ATPase and the 5' and 3' ends of the colonic H(+)-K(+)-ATPase. The resulting products, 300-700 bp in size, hybridized with probes directed against either the gastric or colonic sequences of the H(+)-K(+)-ATPase. Sequencing of the individual PCR products showed identity with the appropriate regions of the alpha-subunits of the gastric H(+)-K(+)-ATPase and colonic H(+)-K(+)-ATPase. These data indicate that the rat kidney expresses mRNAs encoding both gastric and colonic H(+)-K(+)-ATPases.

The role of metabolic acidosis in the pathogenesis of renal osteodystrophy.

Renal osteodystrophy is thought to be the result of abnormalities in the serum levels of parathyroid hormone, vitamin D, calcium, and phosphorus, and excess exposure to certain substances such as aluminum and iron. However, a significant amount of data suggest that the metabolic acidosis that develops in the course of chronic renal failure may also play a contributory role. Metabolic acidosis may effect changes in bone by directly inducing dissolution of bone, stimulating osteoclast-mediated bone resorption, inhibiting osteoblast-mediated bone formation, and altering the serum concentrations or the biological actions of parathyroid hormone and vitamin D. As a consequence, in some patients with normal renal function, osteoporosis and osteomalacia have been reported that are linked in part to metabolic acidosis. Also, in patients with chronic renal failure before and after initiation of dialysis, the severity of the metabolic acidosis appears to have a bearing on the presence and degree of hyperparathyroidism, osteitis fibrosa, and osteomalacia. Taken as a whole, these data suggest that correction of the metabolic acidosis of chronic renal failure may have a beneficial effect on the bone disease observed in these patients. This article reviews (1) the data indicating the mechanisms by which metabolic acidosis causes alterations in bone; (2) the types of bone lesions observed in animals and humans with metabolic acidosis in the presence of normal and abnormal renal function; (3) the impact of correction of the acidosis on the bone lesions; and (4) specific recommendations for treatment in patients with chronic renal failure both before and after initiation of maintenance dialysis.

Basolateral Na(+)-independent Cl(-)-HCO3- exchange in primary cultures of rat IMCD cells.

The role of anion exchange in the regulation of intracellular pH (pHi) under base load and steady-state conditions was investigated in confluent monolayers of rat inner medullary collecting duct (IMCD) cells in primary culture using the pH-sensitive fluoroprobe 2,7-bis(carboxyethyl)-5(6')-carboxyfluorescein (BCECF). Recovery of pHi after imposition of a base load induced either by replacement of HCO3-/CO2 by N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) at the same extracellular pH (pHo) or deletion of Cl- from a HCO3-/CO2-buffered solution had an absolute requirement for Cl-, was Na+ independent, and was inhibited approximately 90% by 50 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). When pHo was decreased by lowering HCO3- concentration in the constant presence of 5% CO2, the rate of decrement in pHi was significantly blunted in the absence of Cl-. Imposition of a positive or negative diffusion potential of equal but opposite magnitude did not modify the anion exchange rate, confirming the electroneutrality of the process. Under steady-state conditions, pHi of cells bathed in a HCO3-/CO2-buffered solution was 7.33 +/- 0.06, significantly lower than that of cells bathed in a nominally HCO3-/CO2-free buffer (7.50 +/- 0.04), indicating that under physiological conditions the pathway functions as a base extruder. In studies performed on cells grown on permeable supports, the anion exchange pathway was found to be confined exclusively to the basolateral-equivalent cell surface. In summary, confluent monolayers of rat IMCD cells in primary culture possess a Na(+)-independent, DIDS-inhibitable electroneutral Cl(-)-HCO3- exchange pathway that is confined to the basolateral cell surface. The transporter is an important determinant of steady-state pHi and is the predominant mechanism whereby the cell recovers from imposed elevations in pHi.

Platelet-activating factor attenuates the arginine vasopressin-induced fall of transepithelial resistance across inner medullary collecting duct monolayers.

Platelet-activating factor (PAF) is a vasoactive substance produced in the medulla which may alter Na excretion by the kidney. To examine a possible site and mechanism of action of PAF on the kidney, we evaluated the effects of PAF on transepithelial resistance and intracellular calcium concentration ([Ca2+]i) in cultured rat inner medullary collecting duct cells. Exposure of inner medullary collecting duct (IMCD) cell monolayers to PAF had no significant effect on basal transepithelial resistance. By contrast, incubation of IMCD cells with PAF reversibly blocked the fall in transepithelial resistance induced by arginine vasopressin (AVP): -11.1 +/- 1.4 omega.cm2 with AVP versus -0.02 +/- 1.6 omega.cm2 with PAF and AVP. Exposure of IMCD cells to PAF in Ca-replete medium caused a rise in intracellular calcium from 155 +/- 25 to 491 +/- 68 nM. By contrast, exposure of IMCD cells to PAF in Ca-free medium produced no change in [Ca2+]i. Because the rise in [Ca2+]i induced by PAF was absent in Ca-free medium, transepithelial resistance across IMCD monolayers was examined in calcium-free medium. The effect of PAF to block the fall in transepithelial resistance induced by AVP was maintained in Ca-free medium. These data suggest that PAF modulates the effect of AVP on conductive channels by a mechanism distinct from changes in intracellular calcium.

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.

AVP reduces transepithelial resistance across IMCD cell monolayers.

The inner medullary collecting duct (IMCD) is an important site of action for arginine vasopressin (AVP). To examine the mode of action of AVP in this segment, we measured the change in transepithelial resistance of cultured rat IMCD cells grown to confluence on collagen-coated Millicell culture plate inserts in response to AVP. Resistance was measured by use of an EVOM voltage-ohm meter. AVP at 10(-11)-10(-8) M caused a fall in resistance of 6.9 +/- 1.3 to 14.0 +/- 1.4 omega.cm2 (P less than 0.05 to less than 0.01 vs. no AVP), which was reversed by removal of AVP or addition of 10(-6) M amiloride. Pretreating the apical surface of IMCD cells with trypsin had no effect on resistance but totally prevented the antidiuretic hormone-induced fall in resistance. Pretreating the apical surface with trypsin and amiloride did not prevent the fall in resistance to AVP. Addition of 10(-9) M AVP or 10(-6) M forskolin increased 2-min adenosine 3',5'-cyclic monophosphate (cAMP) accumulation by 55 or 96%, respectively. Stimulation of endogenous cAMP accumulation by forskolin or the addition of exogenous 8-bromo-cAMP caused no change in resistance. To examine the relationship between intracellular calcium [( Ca2+]i) and AVP action, the response of [Ca2+]i to AVP was measured by use of fura-2. AVP induced no change in [Ca2+]i in IMCD cells in suspension, on glass cover slips, or on permeable supports. Ionomycin (25 nM) increased [Ca2+]i in IMCD cells and lowered resistance across monolayers, but the fall in resistance was not blocked by amiloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of Na+-H+ exchange activity by intracellular Na+, H+, and Li+ in IMCD cells.

In the present study, cultured inner medullary collecting duct (IMCD) cells loaded with the pH-sensitive dye 2',7' bis(carboxyethyl)-carboxyfluorescein were used to study the interaction of H+, Na+, and Li+ with the intracellular face of the Na+-H+ exchanger. The interaction of Na+ with the external face of the exchanger followed simple saturation kinetics with an apparent affinity for Na+ of 19.5 +/- 2 mM (n = 3) at an extracellular pH of 7.4. Extracellular H+ and Li+ inhibit Na+o-H+i exchange, mainly due to interference with Na+ binding to an external site or the same enzyme intermediate species in the turnover cycle of the Na+-H+ exchanger. The interaction of H+ with the internal face of the exchanger does not follow simple saturation kinetics. The calculated Hill coefficient for H+ interaction with intracellular sites was 1.92. Na+ and Li+ also interact with the intracellular face of the Na+-H+ exchanger. This interaction of Li+ and Na+ with internal sites results in inhibition of Na+-H+ exchange activity in the forward direction (Na+ influx/H+ efflux). The inhibitory effect of intracellular Na+ and Li+ is pHi dependent and most apparent under physiological conditions, i.e., at an intracellular pH of 7.1, an extracellular pH of 7.4, and an extracellular Na+ of 140 mM. This study shows the importance of intracellular Na+ concentration in determining exchanger activity.

Detection of a Na+-H+ antiporter in cultured rat renal papillary collecting duct cells.

To examine whether Na+-dependent H+ transport is present in the papillary collecting duct, changes in intracellular pH (pHi) were evaluated in cultured papillary collecting duct cells acidified to a pHi of 6.3 and then placed into Na+-free or Na+-containing solutions. pHi was determined from changes in the fluorescent signal of the pH-sensitive dye BCECF. pHi did not change significantly when cells were placed in tetramethylammonium chloride- or KCl-containing solutions; however, a significant rise in pHi occurred when acid-loaded cells were placed in solutions containing 140 mM NaCl. The Na+-dependent rise in pHi was blocked by high concentrations of amiloride, but was not affected by alterations in membrane potential across the cell. The rate of rise in pHi was a function of extracellular sodium concentration with a Km for Na+ of 30 +/- 12 mM (n = 6). The properties of this Na+-dependent H+ efflux supports the presence of a Na+-H+ antiporter in the papillary collecting duct.

The use of intracatheter instillation of streptokinase in the treatment of recurrent bacterial peritonitis in continuous ambulatory peritoneal dialysis.

Recurrent bacterial peritonitis resistant to therapy with antibiotics is seen in a small percentage of patients maintained on continuous ambulatory peritoneal dialysis. In these patients, removal of the Tenckhoff catheter is necessary to achieve a cure. Sequestration of bacteria within fibrin clots located on the catheter has been postulated to contribute to this resistance to standard therapy. We, therefore, examined the efficacy of intraperitoneal streptokinase in combination with antibiotic therapy in the treatment of two patients with recurrent bacterial peritonitis. After addition of streptokinase to the therapeutic regimen, no further episodes of peritonitis were observed after 6 to 8 weeks follow-up. These data suggest that intraperitoneal streptokinase may be useful as adjunctive therapy in the treatment of recurrent bacterial peritonitis.