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PubMedDate not supplied

Effect of electrode impedance in improved buffer amplifier for bioelectric recordings.

We analysed the effects of electrode impedance on the transfer response of a one-stage improved buffer amplifier. The electrode DC resistance (R(d)) modifies the one-stage buffer transfer response. We found a limit electrode resistance (R(d(lim))) which depends on the transfer damping factor (epsilon). If R(d) is lower than 86.5 komega, the transfer response of the buffer fulfils American Heart Association (AHA) recommendations, but when R(d) is greater than R(d(lim)) it must be cautiously weighed up because its influence in the transfer response becomes appreciable. The maximum R(d) that can be driven by the buffer is 1.2 Momega. Higher values do not fulfil AHA recommendations. Therefore, electrodes with higher impedance should not be used with this kind of buffer. In contrast, when this buffer is used to build in an instrumentation amplifier (IA) for bipolar recording, the common-mode rejection ratio (CMRR) is sensitive to the electrode type used.

Amplifiers, Electronic↗
PubMed2000

Improved dissolution rate of poorly soluble drug by incorporation of buffers.

This study focused on comparing dissolution rates of indomethacin after co-compressing with three different buffers (calcium carbonate, sodium carbonate, and sodium citrate) at pH 2 and 7. Factors affecting the dissolution rate were also examined, such as type and particle size of buffer and weight-to-weight ratio of drug to buffer. It was found that, at pH 7, the release rates of indomethacin with sodium carbonate (< 74 microns, all proportions) and sodium citrate (< 74 microns, 75% loading) at a 20-min test time were about 10-fold and 6-fold greater, respectively, than that of indomethacin alone. When the drug and buffer were compressed into tablets using a tableting machine, the release rates of indomethacin for the control, sodium carbonate incorporated (25% and 75% buffer loading), and sodium citrate incorporated (75% buffer loading) at a 15-min test time were 50%, 90%, 66%, and 67%, respectively.

Buffers↗
PubMed1999

Using difference spectrophotometry to study the influence of different ions and buffer systems on drug protein binding.

Difference spectrophotometry was used to investigate the effect of different ions and buffer systems on the binding of the anti-inflammatory drug tenoxicam to human serum albumin (HSA). Chloride anions, as well as sodium cations, were found to decrease the binding affinity. The effect of chloride ions was greater on the primary binding constant K1, while sodium ions had a greater effect on the secondary binding constant K2. The number of binding sites n1 and n2 were not affected except at 0.12% HSA, for which the presence of sodium ions halved n2. Potassium ions significantly increased K1. The presence of potassium instead of sodium ions increased binding affinity at lower HSA concentrations. The number of binding sites n1 and n2 were fewer in presence of potassium than in the presence of sodium ions except at 0.12% HSA. The divalent calcium and magnesium cations increased the binding affinity of HSA to tenoxicam, with a greater effect on K1. The effect of magnesium ions on K1 occurred when the MgCl2 concentration was increased to 3 and 9 mM, with the former seeming to be a critical concentration. The number of primary binding sites n1 was not affected by calcium ions, but was halved by 1 mM MgCl2. Both calcium and magnesium cations decreased n2, which was halved when the concentration of either cation was increased to 9 mM. The effect of buffer systems on tenoxicam binding to HSA was dependent on HSA concentration. The value of K1 was higher in Sorensen's phosphate buffer than in Tris [tris(hydroxymethyl) aminomethane HCl] buffer when the HSA concentration was 0.04% and 0.16%, while the reverse was observed at 0.08% and 0.12% HSA. The other binding parameters (K2, n1, and n2) were higher in Sorensen's phosphate than in Tris buffer. However; at certain HSA concentrations, the values of such parameters were comparable in both buffer systems.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

Influence of the washing buffer composition on the sensitivity of an enzyme-linked immunosorbent assay using mycobacterial glycolipids as capture antigens.

Immunogenic glycolipids from the cell wall of Mycobacterium tuberculosis are potential capture antigens in enzyme-linked immunosorbent assays (ELISAs) for the serodiagnostis of tuberculosis. Typically, washing steps in ELISAs are performed with buffers containing a detergent. However, Tween-20, the most commonly added detergent, was reported to be able to remove the coating of certain glycolipid antigens from microtitre wells. In order to determine the influence of the washing buffer composition on the results, we measured serum immunoglobulin G (IgG) against three mycobacterial glycolipids by ELISA, conducting three separate experiments with three different buffers: Tris-buffered saline (TBS), TBS plus 0.02% Tween-20 (TBS-Tween), or TBS plus 0.3% bovine serum albumin (TBS-BSA). The capture antigens applied were lipoarabinomannan with the basic arabinose-containing motif (AraLAM), the mannose-capped version of lipoarabinomannan (ManLAM), and trehalose-6,6'-dimycolate (cord factor). All ELISAs achieved acceptable specificities around 95%. The sensitivities, however, varied widely, depending upon the sort of washing buffer used. In 38 patients with sputum smear-positive pulmonary tuberculosis and control groups of 79 patients with non-tuberculosis lung disease and 92 healthy volunteers, the anti-cord factor ELISA achieved 100%, 31.6%, and 60.5% with TBS, TBS-Tween, and TBS-BSA, respectively. Corresponding sensitivity values for AraLAM were 39.5%, 26.3%, and 23.7%, and for ManLAM 94.7%, 65.8%, and 55.3%. We conclude that Tween-20 or BSA should be omitted from the washing buffer in ELISAs, when the capture antigen is of lipid nature.

Adolescent↗
PubMed2004

Electrolyte mass balance during CVVH: lactate vs. bicarbonate-buffered replacement fluids.

OBJECTIVE: To compare the effect of lactate vs. bicarbonate-buffered replacement fluids on electrolyte mass balance during isovolemic continuous veno-venous hemofiltration (CVVH). DESIGN: Randomized controlled study with double cross over. SETTING: Intensive care unit of a tertiary university hospital. PATIENTS AND PARTICIPANTS: Eight patients with acute renal failure (ARF). INTERVENTIONS: Isovolemic CVVH (2L/hr of replacement fluid) was performed in random order with either bicarbonate or lactate-buffered replacement fluid delivered pre-filter. MEASUREMENTS AND RESULTS: Sodium, potassium, chloride, magnesium, and phosphate, were measured in each sample. There was a mass gain of sodium, which was similar under both conditions (bicarbonate: 23.3+/-4.9 mmol/hr, lactate: 22.7+/-3.5 mmol/hr). Mass chloride gains occurred with bicarbonate-buffered replacement fluid only (12.8+/-5.3 mmol/hr), while there was an overall net loss of chloride with lactate fluids (-2.5+/-5.2 mmol/hr), resulting in a significant difference in chloride mass balance (p<0.0001). Magnesium mass balance was negative with bicarbonate buffer only (-0.6+/-0.2 mmol/hr) and also differed significantly from that obtained with lactate fluids (-0.1+/-0.2 mmol/hr, p<0.0001). Phosphate losses (bicarbonate: -1.7+/-0.7 mmol/hr, lactate: -1.7+/-0.5 mmol/hr) were equivalent with both buffers. Potassium mass balance was neutral. CONCLUSIONS: Mass balance during isovolemic CVVH is significantly affected by the type of replacement fluid administered prefilter. Isovolemic CVVH is not isonatremic and the use of bicarbonate-buffered fluid results in a significant accumulation of chloride and a loss of magnesium.

Acute Kidney Injury↗
PubMedDate not supplied

The relative buffering capacities of saliva and moist snuff: implications for nicotine absorption.

Commercial moist snuff products are used by placing a portion of tobacco inside the mouth between the inner cheek or lip and gum. Nicotine is absorbed into the blood stream via transfer across various oral membranes including the buccal mucosa (cheek lining). The resulting salivary pH when a given moist snuff product is placed in the mouth is an important factor for nicotine absorption because it will affect the proportion of free base nicotine that is readily available for absorption. The resulting salivary pH for a given moist snuff product will be determined in part by the relative acid-base buffering capacities of the saliva and moist snuff, as well as the pHs of the saliva and moist snuff prior to coming in contact with one another. In the current study, the acid-base buffering capacities (mu eq/g) of a series of commercial moist snuff products were determined and compared to the acid-base buffering capacity for unstimulated, whole human saliva. The buffering capacities of the moist snuff products were determined to be 10-20 times higher than the buffering capacity of human saliva. The resulting salivary pH ranges after contact between an artifical saliva and the various moist snuff products were also determined; the results were used to predict the proportion of free base nicotine that can be expected to occur in the mouth during the first few minutes of product use. These studies provide a basis for examining and understanding the effects that moist snuff product pHs and buffering capacities may be expected to have on nicotine absorption.

Absorption↗
PubMed2003

Contribution of lactate buffer, glucose and glucose degradation products to peritoneal injury in vivo.

BACKGROUND: Long-term peritoneal dialysis (PD) is associated with the development of functional and structural alterations of the peritoneal membrane. In this study, we investigated the contribution of low pH lactate buffer, high glucose concentration and glucose degradation products to peritoneal injury in a rat peritoneal exposure model. METHODS: Rats received daily 10 ml of either heat-sterilized (3.86% glucose, pH 5.2, n = 8) or filter-sterilized PD fluid (3.86% glucose, pH 5.2, n = 8), or lactate buffer (pH 5.2, n = 8) via a mini vascular access port during a 10 week period. Untreated rats served as controls. RESULTS: The low pH lactate buffer instillation induced pronounced morphological changes including the induction of angiogenesis in various peritoneal tissues and mild damage to the mesothelial cell layer covering the peritoneum. It also evoked a cellular response characterized by an increased mesothelial cell density on the liver, the induction of milky spots and accumulation of omental mast cells in the omentum, and significant changes in the composition of peritoneal leukocytes. The addition of glucose to low pH lactate buffer (filter-sterilized PD fluid) strengthened most, but not all of the responses described above and induced a fibrogenic response. In addition to glucose and low pH lactate buffer, the presence of glucose degradation products (heat-sterilized PD fluid) significantly induced an additional omental milky spot response (P < 0.03) and caused profound mesothelial damage. The vessel density in the omentum and the mesentery was significantly correlated to both the number of tissue mast cells and the hyaluronan content in the peritoneal lavage, which might suggest a role for mast cells and hyaluronan in the induction of angiogenesis. CONCLUSIONS: Instillations of low pH lactate buffer, a high glucose concentration and glucose degradation products contribute differently and often cumulatively to peritoneal injury in vivo.

Animals↗
PubMed1998

Influence of incubation time and rinsing buffer on the distribution of the tracer lanthanum in canine heart muscle.

Lanthanum (La) is an extracellular tracer, which stains the interstitial space and the cell surface. This study investigates to what extent the distribution of lanthanum in the myocardium of cardioplegically arrested non-ischaemic hearts was influenced by (a) different incubation times in La containing fixative, (b) different kinds of buffer for rinsing and postfixation dilution and (c) different degree of cellular oedema. Myocytes exhibiting La surface staining, with and without intracellular La, were quantified and the volume density of myofibrils (VVMf) as a parameter for the degree of cellular oedema was determined morphometrically. Samples were taken immediately after cardiac arrest induced by coronary perfusion with a cardioplegic solution. Tissue blocks 1 mm3 in size were fixed by immersion for different time periods in a fixation solution containing 1.1% La(NO3)3. Fixation was followed by rinsing in cacodylate or phosphate buffer. The postfixation solution also contained either cacodylate or phosphate buffer. For La detection electron spectroscopic imaging (ESI) and electron energy loss spectroscopy (EELS), was used. Our results show: (i) the volume densities do not differ significantly in specimens rinsed and postfixed in cacodylate or phosphate buffers; (ii) the percentage of myocytes with La surface staining depends on the incubation time in La containing fixative, independent of the rinsing buffer; (iii) the percentage of myocytes with intracellular La correlates significantly with the VVMf; (iv) the incubation time with La containing fixative does not significantly affect the intracellular La staining of slightly swollen cells; and (v) intracellular La distribution patterns differ in cacodylate- and phosphate-buffered specimens. Thus, La tracer methods in conjunction with microanalysis are valuable tools to detect alterations in membrane permeability not visible by conventional transmission electron microscopy (cTEM) in non-ischaemic hearts exhibiting a well preserved ultrastructure.

Animals↗
PubMed1980

The thermodynamic-buffer enzymes.

Oxidative phosphorylation operates at optimal efficiency if and only if the condition of conductance matching L33/L11 = square root 1-q2 is fulfilled. In this relation L11 is the phenomenological conductance of phosphorylation, L33 the phenomenological conductance of the load, i.e. the irreversible ATP-utilizing processes in the cell, and q the degree of coupling of oxidative phosphorylation driven by respiration. Since during short time intervals L11 and q are constant whereas L33 fluctuates in the cell, oxidative phosphorylation would only rarely operate at optimal efficiency due to violation of conductance matching. This paper demonstrates that the reversible ATP-utilizing reaction catalyzed by adenylate kinase can effectively compensate deviations from conductance matching in the presence of a fluctuating L33 and hence allows oxidative phosphorylation to operate at optimal efficiency in the cell. Since the adenylate kinase reaction was found to buffer a thermodynamic potential, i.e. the phosphate potential, this finding was generalized to the concept of thermodynamic buffering. The thermodynamic buffering ability of the adenylate kinase reaction was demonstrated by experiments with incubated rat-liver mitochondria. Considerations of changes introduced in the entropy production by the adenylate kinase reaction allowed to establish the theoretical framework for thermodynamic buffering. The ability of thermodynamic buffering to compensate deviations from conductance matching in the presence of fluctuating loads was demonstrated by computer simulations. The possibility of other reversible ATP-utilizing reactions, like the ones catalyzed by creatine kinase and arginine kinase, to contribute to thermodynamic buffering is discussed. Finally, the comparison of the theoretically calculated steady-stae cytosolic adenine nucleotide concentrations with experimental data from perfused livers demonstrated that in livers from fed rats conductance matching is fulfilled on a time average and that the degree of coupling corresponded to qpec = 0.97 permitting the most economic maintenance of a maximal output power of oxidative phosphorylation. For the case of livers from starved rats this analysis suggested that the degree of coupling corresponded to qfec = 0.95, permitting the most economic maintenance of a maximal net rate of ATP synthesis at optimal efficiency of oxidative phosphorylation.

Adenine Nucleotides↗
PubMed1993

Salivary flow rate, buffer effect, sodium, and amylase in adolescents: a longitudinal study.

The study aimed to provide information on salivary secretion rate, buffer effect, sodium, total protein, and amylase in adolescence. Paraffin-wax-stimulated saliva was collected annually in 69 initially 10-yr-olds and in 98 initially 15-yr-olds. During the 5-yr follow-up, the rate of flow increased in both sexes in the younger age group. In the older age group there was only a slight increase in the flow within the 2-yr follow-up. In both age groups, girls tended to have lower secretion than boys. In cross-sectional analyses, the rate of flow correlated positively with buffer effect and sodium, and negatively with proteins. These findings are in line with earlier observations. However, with age, the buffer effect did not parallel the flow. At the base-line examination the buffer effect was lower in the 15-yr-old than in the younger age group. In line with that, a decrease was found at the final examination in the initially 10-yr-olds. This decrease was stronger in girls than in boys. The observed change in the buffer effect was not related to a parallel change in the flow rate or total protein and amylase content of saliva. In girls the change was, however, associated with a small, but statistically significant drop in the salivary sodium level. The variation in the buffer effect increased from the age of 12 to 15, especially in girls. This effect could not be demonstrated for the other flow-rate-associated variables used to monitor the functioning of the salivary glands.

Adolescent↗
PubMed1994

Factors associated with salivary buffering capacity in young adults in Stockholm, Sweden.

The buffering capacity and flow rate of stimulated whole saliva were assessed in 150 persons, 20-24 yr of age. The associations were assessed between the buffer value and the flow rate, some dietary factors, tobacco habits, use of oral contraceptives, and some demographic variables. The results demonstrate that a low flow rate may predict a low buffer value but not a high value. Flow rate accounted for the largest part of the buffering variation but morning and afternoon saliva sampling, female gender, food consumption between meals, and smoking seem to have contributed to low buffering values. Snuff-taking habits, oral contraceptives, and protein consumption between meals were not associated with the buffering capacity.

Adult↗
PubMed1993

Mobile and immobile calcium buffers in bovine adrenal chromaffin cells.

1. The calcium binding capacity (kappa S) of bovine chromaffin cells preloaded with fura-2 was measured during nystatin-perforated-patch recordings. 2. Subsequently, the perforated patch was ruptured to obtain a whole-cell recording situation, and the time course of kappa S was monitored during periods of up to one hour. 3. No rapid change (within 10-20 s) of kappa S was observed upon transition to whole-cell recording, as would be expected, if highly mobile organic anions contributed significantly to calcium buffering. However, approximately half of the cells investigated displayed a drop in kappa S within 2-5 min, indicative of the loss of soluble Ca2+ binding proteins in the range of 7-20 kDa. 4. The average Ca2+ binding capacity (differential ratio of bound calcium over free calcium) was 9 +/- 7 (mean +/- S.E.M.) for the poorly mobile component and 31 +/- 10 for the fixed component. It was concluded that a contribution of 7 from highly mobile buffer would have been detected, if present. Thus, this value can be considered as an upper bound to highly mobile Ca2+ buffer. 5. Both mobile and fixed calcium binding capacity appeared to have relatively low Ca2+ affinity, since kappa S did not change in the range of Ca2+ concentrations between 0.1 and 3 microM. 6. It was found that cellular autofluorescence and contributions to fluorescence of non-hydrolysed or compartmentalized dye contribute a serious error in estimation of kappa S. 'Balanced loading', a degree of fura-2 loading such that the calcium binding capacity of fura-2 equals cellular calcium binding capacity, minimizes these errors. Also, changes in kappa S at the transition from perforated-patch to whole-cell recording can be most faithfully recorded for similar degrees of loading in both situations. 7. Nystatin was found unable to make pores from inside of the plasma membrane of chromaffin cells. With careful preparation and storage the diluted nystatin solution maintained its high activity of membrane perforation for more than one week. 8. An equation for the effective diffusion constant for total cytoplasmic calcium, D'Ca, was derived, which takes into account fixed buffer and poorly mobile buffer as determined, as well as calcium bound to fura-2 and some highly mobile buffers.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Cytoplasmic calcium buffers in intact human red cells.

1. Precise knowledge of the cytoplasmic Ca2+ buffering behaviour in intact human red cells is essential for the characterization of their [Ca2+]i-dependent functions. This was investigated by using a refined method and experimental protocols which allowed continuity in the estimates of [Ca2+]i, from nanomolar to millimolar concentrations, in the presence and absence of external Ca2+ chelators. 2. The study was carried out in human red cells whose plasma membrane Ca2+ pump was inhibited either by depleting the cells of ATP or by adding vanadate to the cell suspension. Cytoplasmic Ca2+ buffering was analysed from plots of total cell calcium content vs. ionized cytoplasmic Ca2+ concentration ([CaT]i vs. [Ca2+]i) obtained from measurements of the equilibrium distribution of 45Ca2+ at different external Ca2+ concentrations ([Ca2+]o), in conditions known to clamp cell volume and pH. The equilibrium distribution of 45Ca2+ was induced by the divalent cation ionophore A23187. 3. The results showed the following. (i) The known red cell Ca2+ buffer represented by alpha, with a large capacity and low Ca2+ affinity, was the main cytoplasmic Ca2+ binding agent. (ii) The value of alpha was remarkably constant; the means for each of four donors ranged from 0.33 to 0.35, with a combined value of all independent measurements of 0.34 +/- 0.01 (mean +/- S.E.M., n = 16). This contrasts with the variability previously reported. (iii) There was an additional Ca2+ buffering complex with a low capacity (approximately 80 micromol (340 g Hb)(-1)) and intermediate Ca2+ affinity (apparent dissociation constant, K(D,app) approximately 4-50 microM) whose possible identity is discussed. (iv) The cell content of putative Ca2+ buffers with submicromolar Ca2+ dissociation constants was below the detection limit of the methods used here (less than 2 micromol (340 g Hb)(-1)). 4. Vanadate (1 mM) inhibited the Vmax of the Ca2+ pump in inosine-fed cells by 99.7%. The cytoplasmic Ca2+ buffering behaviour in these cells was similar to that found in ATP-depleted cells.

Adenosine Triphosphate↗
PubMed1984

Analysis of pH and buffer effects on flucytosine activity in broth dilution susceptibility testing of Candida albicans in two synthetic media.

We examined the influences of different pH levels and three different buffers on flucytosine activity against 12 isolates of Candida albicans in two synthetic media, yeast nitrogen base (YNB) and synthetic amino acid medium-fungal (SAAMF), using broth dilution techniques and measuring the endpoints of visual MICs and turbidimetric 50% inhibitory concentrations. The two media were originally prepared as follows: YNB, unbuffered, pH 5.6; SAAMF, buffered with morpholinepropanesulfonic acid-Tris, pH 7.4; the resultant geometric mean MIC and 50% inhibitory concentration of 5-FC were 78- and 32-fold higher, respectively, in SAAMF. Raising the pH of YNB or lowering the pH of SAAMF had virtually no effect on these differences in MIC and 50% inhibitory concentration in the two media. In contrast, virtually all of the discrepancy appeared to be due to morpholinepropanesulfonic acid-Tris, which exerted concentration-dependent inhibition of flucytosine activity not evident when N-2-hydroxyethylpiperazine-N'-ethanesulfonic acid or phosphate buffer systems were substituted. In other turbidimetric studies, growth was slowed more than 50% in YNB as the pH was raised to 7.4, regardless of which buffer was used. Based on our studies, we recommend modifying the composition of SAAMF by substituting a nonantagonistic buffer if any buffer is to be used with SAAMF in the testing of flucytosine. With this modification, SAAMF warrants further study as a generally applicable medium for fungal-susceptibility testing.

Buffers↗
PubMed2002

Transport of Cryptosporidium parvum oocysts through vegetated buffer strips and estimated filtration efficiency.

Vegetated buffer strips were evaluated for their ability to remove waterborne Cryptosporidium parvum from surface and shallow subsurface flow during simulated rainfall rates of 15 or 40 mm/h for 4 h. Log(10) reductions for spiked C. parvum oocysts ranged from 1.0 to 3.1 per m of vegetated buffer, with buffers set at 5 to 20% slope, 85 to 99% fescue cover, soil textures of either silty clay (19:47:34 sand-silt-clay), loam (45:37:18), or sandy loam (70:25:5), and bulk densities of between 0.6 to 1.7 g/cm(3). Vegetated buffers constructed with sandy loam or higher soil bulk densities were less effective at removing waterborne C. parvum (1- to 2-log(10) reduction/m) compared to buffers constructed with silty clay or loam or at lower bulk densities (2- to 3-log(10) reduction/m). The effect of slope on filtration efficiency was conditional on soil texture and soil bulk density. Based on these results, a vegetated buffer strip comprised of similar soils at a slope of or=3 m should function to remove >or=99.9% of C. parvum oocysts from agricultural runoff generated during events involving mild to moderate precipitation.

Animals↗
PubMed1986

The effects of pH, buffers, and fatty acid concentration on the incorporation of radioactive arachidonate into endogenous neuronal nuclear lipids.

Using neuronal nuclei (N1) isolated from cerebral cortices of 15-day-old rabbits the incorporation of [3H]arachidonate into N1 lipids was followed in vitro. Arachidonate was principally incorporated into triacylglycerol and phosphatidylinositol. When low concentrations (32 mM) of Tris-HC1 (pH 7.4) were used, rates of total arachidonate incorporation were small and phosphatidylinositol received the bulk (greater than 84%) of the arachidonate. When the concentration of Tris-HC1 (pH 7.4) or, in certain cases, the concentration of arachidonate was increased, there was a rise in total arachidonate incorporation into N1, with an increasing proportion of radioactivity entering triacylglycerol until it was the predominantly labelled lipid. Using other buffers (phosphate, imidazole, HEPES, pH 7.4), the shift from phosphatidylinositol to triacylglycerol as principal labelled lipid, with buffer concentration, was not as marked as with Tris-HC1 (pH 7.4). When the buffer concentration was maintained at 107 mM and the pH was lowered to 6.5, the three amine-containing buffers showed a sizeable decline in arachidonate incorporation into N1 lipids and a corresponding decrease in triacylglycerol labelling. The proportion of the total radioactivity in N1 phosphatidylinositol rose as the pH declined. Of the buffers used, Tris-HC1 showed the greatest changes over the pH range. Based upon pK values for the amine buffers, it is suggested that an increased proportion of the protonated amine may be inhibitory to arachidonate incorporation in N1. Studies of acyl-CoA synthetase in N1 indicated this enzyme as the site of the inhibition.

Animals↗
PubMed1985

Influence of buffers on dV/dtmax recovery kinetics with lidocaine in myocardium.

Buffers are reported to modify electrical function of heart tissue. Since electrophysiological actions of antiarrhythmic drugs are examined in different buffer systems, we set out to examine the influence of buffers on lidocaine's electrophysiological actions by measuring recovery kinetics of maximum upstroke velocity (dV/dtmax) in lidocaine solutions buffered with HCO-3-CO2, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), and tris(hydroxymethyl)aminomethane (Tris) at extracellular pH 7.4. Transmembrane potential and dV/dtmax were recorded from guinea pig papillary muscle. Recovery kinetics were determined by introducing progressively earlier test stimuli during diastole. During lidocaine (1.5 X 10(-5) M) exposure, the time constant (Tr) of dV/dtmax recovery significantly increased when 21 mM HCO-3-5% CO2 was replaced by either 5 mM HEPES (38 +/- 8%, mean, +/- SED) or 5 mM Tris (41 +/- 6%). This potentiation of Tr was 1) reversed by increasing Tris to 20 mM, and 2) also abolished by restoring HCO-3-CO2 to HEPES or Tris solutions. Decreasing HCO-3 (21-4 mM) and CO2 (5-1%) increased Tr by 27 +/- 1%. We propose that the mechanism for the potentiation of Tr is therefore related to buffer concentration rather than to the lack of HCO-3-CO2. We speculate that, by reducing surface pH, lowered buffer capacity can slow the rate of dV/dtmax recovery.

Action Potentials↗
PubMed1996

Impact of extracellular buffer composition on cardioprotective efficacy of Na+/H+ exchanger inhibitors.

There is controversy over whether the cardioprotective effects of Na+/H+ exchanger inhibitors are exerted primarily during ischemia or during subsequent reperfusion, possibly because of interstudy differences in experimental conditions. We studied the impact of perfusate buffer composition on the relative degree of protection afforded by Na+/H+ exchanger inhibition during ischemia vs. reperfusion. Isolated rat hearts (n = 8/group) were perfused (37 degrees C, 75 mmHg) with bicarbonate- or N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium and subjected to 20 min of global zero-flow ischemia and 45 min of reperfusion. One of two structurally distinct Na+/H+ exchanger inhibitors [5-(N,N-dimethyl)amiloride (DMA) or (3-methylsulfonyl-4-piperidinobenzoyl)guanidine methanesulfonate (HOE-694), 10 mumol/l] was transiently (5 min) infused 1) immediately before ischemia, 2) during initial reperfusion, or 3) during both of these periods. With bicarbonate-buffered medium, neither drug improved the postischemic recovery of left ventricular developed pressure (LVDP) when given only during reperfusion. In contrast, HOE-694 improved the postischemic recovery of LVDP from 39 +/- 5% in control to 66 +/- 6% (P < 0.05) when given before ischemia and from 33 +/- 4% in control to 65 +/- 4% (P < 0.05) when given before ischemia plus during reperfusion. With the latter protocol, the cardioprotective effect of HOE-694 occurred in a dose-dependent manner at 0.1-10 mumol/l. In contrast to the results with bicarbonate-buffered medium, in the presence of N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium, DMA and HOE-694 significantly improved recovery of LVDP (from 34 +/- 5% in controls to 56 +/- 3 and 71 +/- 8%, both P < 0.05) when given only during reperfusion. They also provided significant protection when given before ischemia or before ischemia plus during reperfusion; with the latter protocol, HOE-694 produced an almost complete recovery of LVDP (88 +/- 9 vs. 30 +/- 7% in controls, P < 0.05). In conclusion, our results suggest that the influence of Na+/H+ exchanger activity during reperfusion on the extent of functional recovery is modulated significantly by perfusate buffer composition. As a consequence, the cardioprotective efficacy of Na+/H+ exchanger inhibitors may be overestimated under bicarbonate-free conditions.

Amiloride↗