Developmental changes in intracellular pH buffering power in smooth muscle

 Intracellular pH (pH_i) is known to modulate contraction. Neonatal tissues can differ from adult tissue in contractile response to stimuli known to alter pH_i e.g. hypoxia. Changes of pH are attenuated by buffering, thus any difference in buffering power (β) between tissues could affect their functional response to pH_i perturbation. Similarly the extent to which any extracellular pH (pH_o) alteration is transmitted into a pH_i change will also influence function. We have therefore determined the intrinsic β and effect of pH_o change on pH_i in neonatal and adult ureteric, uterine and gastric smooth muscles using the pH-sensitive fluorophore carboxy-SNARF. β was found to be similar in the three adult tissues, but there were significant differences between neonatal tissues. In contrast, we found little difference in the amount of pH_i change produced by pH_o change between neonatal and adult tissues from the same smooth muscle, but a difference between smooth muscles. These data highlight significant differences between smooth muscles and their developmental state, which may contribute to different degrees of protection when pH is perturbed. Received: 17 October 1997 / Received after revision: 27 November 1997 / Accepted: 28 November 1997     

Environmental effects on the growth and proteolysis of Treponema denticola ATCC 33520

The effect of pH, redox potential, O₂ and H₂ on the growth and proteolytic activity of Treponema denticola ATCC 33520 was studied in a chemostat at different growth rates. The peptidase and protease activities were estimated using different amido-methyl coumarin derivatives and azocasein. The maximum growth rate of T. denticola ATCC 33520 was 0.14 h⁻¹. Reduction of the growth rate of T. denticola by 50–60% gave: an increase in cell mass of 150–200%, a higher acetogenesis and a shift of the pH optimum. The protease and phenylalanine peptidase activities seemed to be of greater importance for the growth of T. denticola ATCC 33520 than the rather low arginine and proline peptidase activities. The redox potential (E_h) played a secondary role. At microaerophilic conditions with 1–5% O₂, the cultures maintained a redox potential below −311 mV and an optimal acetogenesis. The presence of H? induced a marked growth stimulation of T. denticola ATCC 33520. It is concluded that the cell mass and proteolytic activity of T. denticola ATCC 33520 are modulated by the growth rate and the pH and to a lesser extend by the redox potential and presence of O₂. Stagnation of the exudate-flow influences these factors and will lead to an increase of the spirochetal population and proteolysis in the periodontal pocket.     

Defective Acidification in Human Breast Tumor Cells and Implications for Chemotherapy

Multidrug resistance (MDR) is a significant problem in the treatment of cancer. Chemotherapeutic drugs distribute through the cyto- and nucleoplasm of drug-sensitive cells but are excluded from the nucleus in drug-resistant cells, concentrating in cytoplasmic organelles. Weak base chemotherapeutic drugs (e.g., anthracyclines and vinca alkaloids) should concentrate in acidic organelles. This report presents a quantification of the pH for identified compartments of the MCF-7 human breast tumor cell line and demonstrates that (a) the chemotherapeutic Adriamycin concentrates in acidified organelles of drug-resistant but not drug-sensitive cells; (b) the lysosomes and recycling endosomes are not acidified in drug-sensitive cells; (c) the cytosol of drug-sensitive cells is 0.4 pH units more acidic than the cytosol of resistant cells; and (d) disrupting the acidification of the organelles of resistant cells with monensin, bafilomycin A1, or concanamycin A is sufficient to change the Adriamycin distribution to that found in drug-sensitive cells, rendering the cell vulnerable once again to chemotherapy. These results suggest that acidification of organelles is causally related to drug resistance and is consistent with the hypothesis that sequestration of drugs in acidic organelles and subsequent extrusion from the cell through the secretory pathways contribute to chemotherapeutic resistance.     

A comparison of the effects of omeprazole and ranitidine on gastric secretion in women undergoing elective Caesarean section

This study compares the efficacy of omeprazole and ranitidine at reducing gastric secretion in obstetric patients. Sixty-five women scheduled to undergo elective Caesarean section under general anaesthesia were randomly allocated to receive either omeprazole 40 mg or ranitidine 150 mg orally at 2200 hours the night before and at 0600 hours on the morning of surgery. Intragastric pH and volume were measured immediately after induction of anaesthesia and on completion of surgery. All patients had gastric aspirates less than 25 ml. None of the omeprazole group had an aspirate of pH less than 3.5. Six patients (19%) in the ranitidine group had aspirates of pH less than 3.5, a significant difference from the omeprazole group (p less than 0.05). Of these six, two (6%) had aspirates of pH less than 2.5. Hence this study showed that omeprazole was more effective and consistent than ranitidine at maintaining gastric pH greater than 3.5.     

Ambulatory 24-hour esophageal pH monitoring

If 24-hour esophageal pH monitoring is to be a useful diagnostic tool, it must reliably discriminate gastroesophageal reflux patients despite daily variations in distal esophageal acid exposure. To address this issue, we studied 53 subjects (14 healthy normals, 14 esophagitis patients, and 25 patients with atypical symptoms) with two ambulatory pH tests performed within 10 days of each other. Intrasubject reproducibility of 12 pH parameters to discriminate the presence of abnormal acid reflux was determined. As a group, the parameters of percent time with pH<4 (total, upright, recumbent) were most reproducible (80%). Therefore, a subject was defined as having gastroesophageal reflux disease if at least one of these three values were abnormal. Intrasubject reproducibility for the diagnosis of reflux disease was 89% for the entire sample. Among subsets, the reproducibility was 93% for the normals and esophagitis patients and 84% for the atypical symptom patients. Total percent time with pH<4 was the single most discriminate pH parameter (85%) and nearly equaled that of the three combined parameters (89%). The intrasubject variability of this parameter was determined by the mean ±2sd of the relative differences between the two test results for all 53 subjects. Total percent time with pH<4 may vary between tests by a factor of 3.2-fold or less (218% higher to 69% lower). We conclude: (1) ambulatory 24-hr esophageal monitoring is a reproducible test for the diagnosis of gastroesophageal reflux disease; and (2) the large intrastudy variability in 24-hr total acid exposure may limit this test's usefulness as a measurement of therapeutic improvement.Supported, in part, by Public Health Services Grant AM 34200-01A1 from NIADDIK.     

The effect of pH and nucleophiles on complement activation by human proximal tubular epithelial cells.

BACKGROUND: Activation of urinary complement proteins in situ by proximal tubular epithelial cells (PTEC) may contribute to the mediation of tubulointerstitial injury in patients with significant proteinuria. However, the mechanism involved is unclear, and the role of changes in urinary pH and in the concentrations of urea or ammonia requires further clarification. METHODS: The protein fraction of urine samples from nine patients with proteinuria >1.5 g/day was purified. A cell ELISA involving cultured HK-2 PTEC was used to investigate the capacity of urinary protein to promote the deposition of both C3 and C9 on the cell surface. The effect of variations in pH (5.5-8.0) and in the concentration of urea and ammonia was also examined. C3 was purified and used to further investigate the mechanism of complement deposition. RESULTS: Urine samples from the majority of patients induced deposition of C3 and C9 on the surface of HK-2 cells via the alternative pathway. This process was maximal at acidic pH values. Preincubation of urinary complement or serum with urea or ammonia inhibited C3 deposition. Purified C3 incubated with HK-2 cells showed no evidence of activation in the absence of other complement components. CONCLUSIONS: These data suggest that bicarbonate protects against complement-mediated damage in the lumen by increasing the local pH, rather than by inhibiting the generation of ammonia. PTEC appear to activate complement through provision of a 'protected site' on their surface, rather than by the activation of C3 by convertase-like protease(s).     

Impact of Ingested Liquids on 24-Hour Ambulatory pH Tests

A prospective investigation of the impact ofingested liquids on 24-hr pH test scores was conducted.Eighty-two patients contributed 142 samples. The liquidsused were coffee/tea (N = 35), water (N = 32), fruit juice (N = 29), cola (N = 34), and beer (N =12). The pH of cola, juice, and beer are approximately3.0. The parameters studied included: total test time,total drink time, total minutes of pH < 4.0 during drink, minutes of pH < 4.0 10 min beforedrink, and minutes of pH < 4.0 10 min followingdrink. Analysis was performed using one-way ANOVA andrepeated measures. Age of patients, total test time, and total time pH < 4.0 were notsignificantly different (P > 0.05). The total time toconsume the drink was significantly greater (P <0.05) for beer than all other liquids. The total time(7.7 ± 6.0 min) pH < 4.0 for cola wassignificantly different (P < 0.023) than beer (3.3± 3.7 min), tea/coffee (1.4 ± 6.5 min),and water (1.1 ± 2.5 min). The percentage oftotal time pH < 4.0 was not significantly different (P >0.05) among any of the liquids. The percentage of timepH < 4.0 during the drink was the highest for cola(63 ± 47%) and juice (51 ± 57%); water,coffee/tea, and beer were not significantly different (P> 0.05). Although the impact of cola and juice werethe greatest, none of these had an impact that exceeded0.5%. The lack of impact of beer appears to be due to the increased period of time it takes toconsume. We conclude that the impact of ingested fluidsis minimal and can probably be disregarded in mostpatient groups.     

Effect of single-dose omeprazole and ranitidine on gastric juice acidity and volume in patients undergoing laparotomy

The effects of oral omeprazole and oral ranitidine on gastric fluid volume and pH were compared in 95 elective surgical patients, randomly assigned to one of three groups. The patients received either 80 mg of omeprazole or 300 mg of ranitidine orally at 6.00 on the morning of surgery. One third of the patients received no antacid therapy. Following induction, a no. 18 nasogastric tube was passed into the stomach and all available gastric fluid was aspirated. pH and volumes were measured. In the omeprazole- and ranitidine-treated groups, the mean pH was > 5.4 after induction, at completion of surgery and 1 h after operation, although at least one patient in both groups had pH < 2.5. The volumes of gastric aspirates were reduced equally by both drugs. Two patients in the omeprazole group, none in the ranitidine group and eight in the control group (26%) had pH <2.5 with volume> 25 ml at induction. Both drugs appeared to be effective in reducing the volume of intragastric fluid and acidity to acceptable values.     

An Accurate Prediction of the pH Change Due to Degradation: Correction for a “Produced” Secondary Buffering System

Esmolol hydrochloride degrades in aqueous solutions by the hydrolysis of a labile aliphatic carboxy-ester group. The products are methanol and ASL-8123. The resulting aliphatic carboxylic acid moiety (ASL-8123) has a pK of 4.80, which is within 1 pH unit of the pH of the formulation. ASL-8123 therefore acts as a secondary buffer and minimizes the change in pH due to degradation. Equations are presented to calculate the change in the pH when the primary degradation product acts as a secondary buffer. This information can be used in the development of a parenteral product to predict, a priori, the concentration of buffer necessary for optimal pH maintenance. This knowledge can reduce the number of formulation screens required to determine the necessary buffer capacity for optimal drug stability.