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J T Daugirdas

Publications and source records attributed to J T Daugirdas.

At least 19 recordsLinked to original sources
PubMed1996

Effect of access recirculation on the modeled urea distribution volume.

The effect of vascular access recirculation (AR) on the modeled urea distribution volume (V) is not straightforward. When blood is sampled properly so that it is not admixed with recirculated blood, AR will cause an unexplained increase in V in cases in which AR is present throughout the dialysis session (when AR is limited to the terminal portion of a dialysis session it will cause little or no change in the modeled V). On the other hand, when blood is sampled from the arterial line after simply stopping the pump, postdialysis blood urea nitrogen (BUN) represents arterial line BUN and does not always reflect the BUN in the patient's blood. Under these conditions, when AR is present throughout the dialysis session the modeled V usually shows an unexplained decrease, but V may be unchanged, depending on the urea reduction ratio (URR). We performed a mathematical analysis to predict when V would be decreased and when it would be unchanged when the postdialysis BUN is contaminated with admixed blood. The analysis revealed that when AR is present uniformly throughout the dialysis session, the modeled V should be underestimated when the URR is < or = O.70. When the URR is greater than 0.70, even severe degrees of AR may not be reflected by a change in V. When AR is limited to the terminal part of the dialysis session or when AR increases during the dialysis session, and when V is based on admixed postdialysis blood, underestimation of V will occur in almost all circumstances. In a cross-sectional comparison of modeled to anthropometric volume ratios in eight patients with severe AR and in 11 controls, and in sequential modeling studies in a single patient in whom severe AR developed gradually over time, the volume ratio was low in most, but not all instances when modeled V was based on an admixed postdialysis BUN sample.

Aged↗
PubMed1996

The dose of hemodialysis and patient mortality.

The relationship between the delivered dose of hemodialysis and patient mortality remains somewhat controversial. Several observational studies have shown improved patient survival with higher levels of delivered dialysis dose. However, several other unmeasured variables, changes in patient mix or medical management may have impacted on this reported difference in mortality. The current study of a U.S. national sample of 2,311 patients from 347 dialysis units estimates the relationship of delivered hemodialysis dose to mortality, with a statistical adjustment for an extensive list of comorbidity/risk factors. Additionally this study investigated the existence of a dose beyond which more dialysis does not appear to lower mortality. We estimated patient survival using proportional hazards regression techniques, adjusting for 21 patient comorbidity/risk factors with stratification for nine Census regions. The patient sample was 2,311 Medicare hemodialysis patients treated with bicarbonate dialysate as of 12/31/90 who had end-stage renal disease for at least one year. Patient follow-up ranged between 1.5 and 2.4 years. The measurement of delivered therapy was based on two alternative measures of intradialytic urea reduction, the urea reduction ratio (URR) and Kt/V (with adjustment for urea generation and ultrafiltration). Hemodialysis patient mortality showed a strong and robust inverse correlation with delivered hemodialysis dose whether measured by Kt/V or by URR. Mortality risk was lower by 7% (P = 0.001) with each 0.1 higher level of delivered Kt/V. (Expressed in terms of URR, mortality was lower by 11% with each 5 percentage point higher URR; P = 0.001). Above a URR of 70% or a Kt/V of 1.3 these data did not provide statistical evidence of further reductions in mortality. In conclusion, the delivered dose of hemodialysis therapy is an important predictor of patient mortality. In a population of dialysis patients with a very high mortality rate, it appears that increasing the level of delivered therapy offers a practical and efficient means of lowering the mortality rate. The level of hemodialysis dose measured by URR or Kt/V beyond which the mortality rate does not continue to decrease, though not well defined with this study, appears to be above current levels of typical treatment of hemodialysis patients in the U.S.

Female↗
PubMed1996

Effect of the dialysis membrane on mortality of chronic hemodialysis patients.

Mortality of prevalent chronic hemodialysis patients remains high. The potential effect of the dialysis membrane on this mortality has not been previously investigated in a large population of chronic hemodialysis patients. Using data from the United States Renal Data System (USRDS), we analyzed a random sample of 6,536 patients receiving hemodialysis on December 31, 1990. The study design was a historical prospective study. By limiting the study to patients dialyzed for at least one year with bicarbonate dialysate, in whom the dose of dialysis could be calculated, and in whom dialysis membrane and co-existing morbidities were defined, the sample size was reduced to 2,410 patients. A Cox proportional hazards model was used to estimate relative mortality risk. The types of dialysis membranes used were broadly classified into three categories: unsubstituted cellulose, modified cellulose (generally cellulose membranes that have been modified by substitutions of some or most of their hydroxyl moieties) and synthetic membranes that are not cellulose-based. The results of the study suggest that after adjusting for the dose of dialysis and the presence of co-morbid factors, the relative risk of mortality of patients dialyzed with modified cellulose or synthetic membranes was at least 25% less than that of patients treated with unsubstituted cellulose membranes (P < 0.001). To account for the possibility that these differences were due to regional practice patterns, we further stratified the data for nine different regions. There was still a 20% difference in relative risk of mortality between membrane groups with the mortality statistically significantly less in patients treated with synthetic membranes (P < 0.045) compared to patients dialyzed with unsubstituted cellulose membranes. The results of this study suggest that the dialysis membrane plays an important role in the outcome of chronic hemodialysis patients. However, more definitive studies are needed before a cause and effect relationship can be proven.

Cellulose↗
PubMed1996

Cardiac output and urea kinetics in dialysis patients: evidence supporting the regional blood flow model.

The regional blood flow model predicts that urea sequestration occurs in organs rather than cells, and that post-dialysis urea rebound is a function of both cardiac index (CI) and regional blood flow distribution to muscle. We measured cardiac output (CO) in 100 randomly selected dialysis patients using bioelectric impedance three times during a single dialysis. Mean CO was 5.8 +/- 2.1 liter/min and CI averaged 3.1 +/- 1.1 liter/min/M2. CI was negatively correlated with age (r = -0.48, P < 0.01). CI was strongly affected by vasodilator ingestion (yes, N = 36, CI = 3.5 +/- 1.2; no, N = 64, CI = 2.88 +/- 0.92, P < 0.006). CI was not associated with systolic, diastolic, or mean blood pressures, nor with Hct, although very few severely anemic patients were in the cohort. Repeat intra-dialytic CO measurements two to three months later in 15 patients with low CI (2.59 +/- 0.59 liter/min/M2) and in 13 patients with high CI (5.00 +/- 0.9, P < 0.001) during a urea kinetic modeling session including 30 minutes post-dialysis rebound, sampling showed highly reproducible values for CO, with a mean absolute value % difference between CO values measured several months apart of 9.0 +/- 17%, r = 0.92. Urea rebound expressed as the difference (delta Kt/V30) between equilibrated and single-pool Kt/V was lower in the high CI group (-0.099 +/- 0.07) than in the low CI group (-0.16 +/- 0.06, P = 0.026), and delta KT/V30 as well as delta Kt/V30 divided by K/V correlated with CI (r = 0.48 and 0.48, respectively, P < 0.01). The RBF model was used to compute a group mean predicted delta Kt/V30 for the low CI and high CI groups based on measured group mean values for CI and K/V. The predicted delta Kt/V30 values for the high CI group (-0.097) and the low CI group (-0.183) agreed closely with measured values. RBF modeled values of CO (7.46 +/- 2.96 liter/min) were not significantly different from impedance-derived CO (6.93 +/- 2.70 liter/min), and the two CO measures correlated significantly (r = 0.63, P = 0.0003). The results provide support for the regional blood flow model of urea kinetics.

Adult↗
PubMed1996

Equations for normalized protein catabolic rate based on two-point modeling of hemodialysis urea kinetics.

The normalized protein catabolic rate (PCRn) can be calculated from predialysis and postdialysis BUN measurements in patients receiving intermittent dialysis. This measure of net protein catabolism, adjusted for body size, is a useful clinical measure of nutrition that correlates with patient outcome and, in patients who are in nitrogen balance, is a reasonable estimate of dietary protein intake. Whereas simplified formulae that estimate the per-treatment dose of hemodialysis, expressed as Kt/Vurea (Kt/V), are in common use, simplified methods for determining PCRn have only recently appeared. In the study presented here, equations were derived for calculating PCRn from the predialysis BUN and Kt/V. The equations were of the general form: PCRn = C0/(a + bKt/V + c/(Kt/NLL)) + 0.168, where Co is the predialysis BUN in mg/dL. Three sets of coefficients were developed for patients dialyzed thrice weekly: one for patients dialyzed after the long interval at the beginning of the week, one for patients dialyzed at midweek, and the third for patients dialyzed at the end of the week. Two similar sets of coefficients were developed for patients dialyzed twice weekly. For patients with remaining function in the native kidney remnant, equations were developed and refined for upgrading PCRn by adjusting C0 upward. The equations were validated by comparing the calculated PCRn with PCRn determined by a formal iterative model of urea kinetics in a series of 119 dialyses in 51 patients dialyzed thrice weekly (r = 0.9952; mean absolute error, 1.97 +/- 1.39%) and in a series of 71 dialyses in 25 patients dialyzed twice weekly (r = 0.9956; mean absolute error, 2.17 +/- 1.56%). These simple yet accurate equations should be useful in epidemiologic studies or in clinical laboratories where limited data are available for each patient or when iterative computer techniques cannot be applied.

Algorithms↗
PubMed1995

Collection of a representative fraction of total spent hemodialysate.

We describe a method of obtaining a small representative fraction of spent dialysate by placing a side tube in the dialysate drainage tube. The side tube, capped with a small-gauge needle, is used to collect the specimen. Fractions obtained in this fashion are found to have a composition similar to that of the remaining spent dialysate.

Hemodialysis Solutions↗
PubMed1995

Simplified equations for monitoring Kt/V, PCRn, eKt/V, and ePCRn.

Although computer solution of the differential equations used in urea kinetic modeling has its advantages, simplified formulas that are actually approximate algebraic solutions to the same equations in the clinically useful range are also useful. The Kt/V can be resolved from the predialysis to postdialysis urea nitrogen ratio (R), the weight loss (UF), session length in hours (t), and anthropometric or modeled volume (V) using the equation: KtV = In (R - 0.008 x t) + (4 - 3.5 x R) x 0.55 UF/V. The equilibrated Kt/V (eKTV) can be estimated from the single-pool arterial Kt/V (spaKTV) or the single-pool venous Kt/V (spmvKTV) using a rate equation based on the regional blood flow model of urea kinetics: eKTV = spaKTV - (0.60)(spaKTV)/t + 0.03 = spmvKTV - (0.46) (spmvKTV)/t + 0.02. The normalized protein catabolic rate (PCRn) can be determined from either the single-pool or equilibrated Kt/V based on the predialysis urea nitrogen level (C0) and the Kt/V (KTV) using the generalized equation: PCRn = C0/(a + bKTV + c/ + KTV) + 0.168, where the constants a, b, and c vary depending on the dialysis schedule and the time of the week that the predialysis blood specimen has been drawn. Such equations can be used either for retrospective surveys, or for quality assurance purposes, as well as for bedside guidance in an individual patient. The actual modeled urea distribution volume can also be easily computed if some effort is made to estimate the dialyzer urea clearance.

Blood Urea Nitrogen↗
PubMed1995

Effect of dialysate temperature on central hemodynamics and urea kinetics.

Use of cool dialysate is associated with increased intradialytic blood pressure, but the hemodynamic mechanism is unknown. Whether changes in dialysate temperature affect muscle blood flow, which may the alter the degree of urea compartmentalization, also is unknown. We measured hemodynamics and blood and dialysate-side urea kinetic indices in nine hemodialysis patients during two cool (35.0 degrees C) versus two warm (37.5 degrees C) dialysate treatments. The % change in mean arterial pressure was different when using the cool (+6.5 +/- 9.7 mm Hg) versus the warm (-13.4 +/- 3.6) dialysate (P < 0.01), despite comparable amounts of fluid removal. Percent changes in cardiac output were similar with the two dialysates, and thus the blood pressure effect was due primarily to changes in total peripheral resistance (% delta TPR, cool +26 +/- 13.6, warm +8.6 +/- 14.5; P < 0.02). During cool dialysate use tympanic membrane temperature changed by -0.51 +/- 0.23 degree C, whereas body temperature increased by 0.52 +/- 0.14 degree C during use of warm dialysate. Measured urea recovery normalized to the predialysis urea nitrogen concentration was similar with the two treatments: cool 31.3 +/- 0.039 liter-1; warm 29.7 +/- 0.021; P = NS. In a second study, post-dialysis urea rebound values from 15 seconds to 30 minutes, expressed as the percent of the post-dialysis SUN, were similar after the two treatments: cool 11.79 +/- 1.4; warm 12.21 +/- 2.27, P = NS.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMed1995

Estimating equilibrated Kt/V from an intradialytic sample: effects of access and cardiopulmonary recirculations.

The Smye method has been proposed to estimate the equilibrated post-dialysis BUN based on an additional intradialytic sample obtained approximately one hour into dialysis. However, the effects of access recirculation (AR) and cardiopulmonary recirculation (CPR) on the Smye computation and the corresponding details of how blood is sampled have not been studied. We examined the accuracy of two variations of the Smye technique. In one method, the intradialytic and postdialysis blood samples were obtained at full blood flow. In the other, the samples were obtained after two minutes of slow flow, to obviate the effects of both AR and CPR. Seventeen patients undergoing high efficiency dialysis and three- to four-hour treatment times were studied, in whom substantial AR was excluded based on two-minute slow flow urea rebound measurements during and just after dialysis. In this group equilibrated Kt/V (eKt/V) values computed using the Smye-derived equilibrated postBUN estimates (full flow samples, 1.22 +/- 0.058 SEM, slow flow samples, 1.23 +/- 0.064) were similar to eKt/V calculated from the 30-minute postdialysis BUN specimen (1.23 +/- 0.049, P = NS). In eight other patients with severe AR (mean 35% +/- 4.5), the accuracy of the full flow Smye estimates was poor when the degree of AR was not constant throughout the dialysis session. Accuracy of the slow flow Smye estimates of eKt/V was unaffected by the presence of severe AR. One advantage of using the full flow Smye method, however, was that a large delta Kt/V value ( < -0.40) was highly suggestive of severe AR.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Circulation↗
PubMed1995

Intracellular acidification associated with changes in free cytosolic calcium. Evidence for Ca2+/H+ exchange via a plasma membrane Ca(2+)-ATPase in vascular smooth muscle cells.

The purpose of this study was to define the mechanism whereby agonists that increase free cytosolic calcium (Cai2+) affect intracellular pH (pHi) in smooth muscle. Rat aortic vascular smooth muscle cells grown on coverslips were loaded with BCECF/AM or fura-2/AM for continuous monitoring of pHi or Cai2+, respectively, in a HCO3-/CO2- containing medium. Recovery from rapid increases in Cai2+ produced by 1 microM angiotensin (Ang) II (delta Cai2+ -229 +/- 43 nM) or 1 microM ionomycin (delta Cai2+ -148 +/- 19 nM) was accompanied by a fall in pHi (delta pHi, -0.064 +/- 0.0085 P < 0.01, and -0.05 +/- 0.012 pH units, P < 0.01, respectively). Neither the fall in pHi nor the rise in Cai2+ elicited by Ang II was prevented by pretreatment with agents which block the action of this agonist on pHi via the stimulation of the Cl/HCo3 exchangers (DIDS, 50 microM) or the Na+/H+ antiporter (EIPA, 50 microM). In the presence of DIDS and EIPA, Ang II produced a fall in pHi (delta pHi, -0.050 +/- 0.014, P < 0.01) and a rise in Cai2+ (delta Ca2+ 252 +/- 157 nM, P < 0.01). That the change in pHi was secondary to changes in Cai2+ was inferred from the finding that, when the rise in Cai2+ elicited by Ang II was prevented by preincubation with a Ca2+ buffer, BAPTA (60 microM), the fall in pHi was abolished as well (delta pHi, 0.0014 +/- 0.0046). The pHi fall produced by Ang II and ionomycin was prevented by cadmium at a very low concentration (20 nM) which is known to inhibit plasma membrane Ca(2+)-ATPase activity (delta pHi -0.002 +/- 0.0006 and -0.0016 pH units, respectively). Cadmium also blunted Cai2+ recovery after Ang II and ionomycin. These findings suggest that the fall in pHi produced by these agents is due to H+ entry coupled to Ca2+ extrusion via the plasma membrane Ca(2+)-ATPase. Our results indicate that agonists that increase Cai2+ cause intracellular acidification as a result of Ca2+/H+ exchange across the plasma membrane. This process appears to be mediated by a plasma membrane Ca(2+)-ATPase which, in the process of extruding Ca2+ from the cell, brings in [H+] and thus acidifies the cell.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

A nomogram approach to hemodialysis urea modeling.

Two sets of nomograms were developed for modeling hemodialysis urea kinetics. The first set is designed to arrive at an initial dialysis prescription. One nomogram estimates the mass transfer area coefficient (KoA) based on urea clearances of a dialyzer, based on urea clearances provided in the manufacturer's product literature. A second nomogram uses the dialyzer KoA value to estimate the expected in vivo urea clearance (K) based on the nominal blood flow rate. The computations include corrections for blood flow-related errors in urea clearance, blood water content, and cardiopulmonary recirculation. Mean urea clearance measured in a series of patients was 226 +/- 22 mL/min and did not differ significantly from mean clearance estimated using this nomogram (232 +/- 8 mL/min). Another pair of nomograms, based on an anthropometric formula, can be used to estimate urea distribution volume (V) from patient sex, height, and weight. The first set of nomograms is designed to estimate an initial dialysis prescription because the nomograms propose an estimated K and an estimated V. Once the target Kt/V is chosen, the appropriate initial treatment time (t) is computed algebraically. The second set of nomograms was developed to verify delivery of the dialysis prescription and to estimate the normalized protein catabolic rate (PCRn). Kt/V is estimated from the postdialysis to predialysis blood urea nitrogen ratio and the ratio of ultrafiltrate volume to postdialysis weight (UF/W). The PCRn is estimated from the predialysis blood urea nitrogen and Kt/V. In a series of 115 patients, Kt/V and PCRn determined from the nomograms correlated highly with corresponding values determined from formal urea modeling (r = 0.99).(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1994

Use of MQAE for measurement of intracellular [Cl-] in cultured aortic smooth muscle cells.

A novel fluorescent indicator, N-[ethoxycarbonylmethyl]-6-methoxy-quinolinium bromide (MQAE), was used to measure intracellular chloride concentration ([Cl-]i) in primary cultures of rat aortic smooth muscle cells (VSMC). The hydrolytic and fluorescent properties of the dye were characterized. The intracellular Stern-Volmer constant was calculated to be 25 M-1. Cl- efflux curves were characteristic of saturation-type kinetics, with an apparent Michaelis-Menten constant value of 11 +/- 4.8 (SD) mM, a maximum velocity of 0.038 +/- 0.021 mM/s, and a half time (t1/2) of 9.0 +/- 3.7 min. The average efflux rate in the first 10 min (0.023 +/- 0.004 mM/s) was reduced in the presence of either 130 microM 4,4'-diisothiocyanato-dihydrostilbene-2,2'-disulfonic acid (H2DIDS) (0.014 +/- 0.006, P = 0.02) or 40 microM furosemide (0.017 +/- 0.004, P = 0.04). Restoration of physiological extracellular chloride concentration ([Cl-]o) after zero Cl- resulted in net Cl- influx with a t1/2 of 3.6 +/- 1.0 min. The initial Cl- influx rate was reduced after exposure to furosemide, from 0.069 +/- 0.006 to 0.046 +/- 0.008 mM/s, P < 0.002, and was reduced after exposure to H2DIDS from 0.102 +/- 0.013 to 0.033 +/- 0.003 mM/s, P < 0.001. Furosemide reduced the steady-state [Cl-]i from 31.6 +/- 3.2 to 26.1 +/- 2.4 mM, P < 0.01, whereas H2DIDS had little effect on [Cl-]i. Our results demonstrate that MQAE can be used to measure [Cl-]i in primary cultures of VSMC.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

Employing L-lactic acid powder in the preparation of a dry "acid concentrate" for use in a bicarbonate-based dialysis solution-generating system: experience in hemodialysis patients.

By replacing the liquid acetic acid present in the "acid concentrate" of a bicarbonate-based dialysis solution-generating system with an equimolar amount of solid L-lactic acid and by using the dry forms of the remaining constituents, we were able to create a dry "acid concentrate" just prior to use, and successfully employed this "acid concentrate" to produce a bicarbonate-based solution to hemodialyze patients.

Bicarbonates↗
PubMed1994

Adverse effects of dialyzers manifesting during the dialysis session.

The intradialytic symptoms that can be linked to components of the extracorporeal circuit of greatest clinical importance are the Type A (anaphylactoid) reactions. Most of these are IgE-mediated reactions due to ethylene oxide and are preventable by adequate degassing of the dialyzer by the manufacturer and by adequate rinsing of the dialyzer just prior to use. AN69-associated reactions are a second group, and are probably mediated by membrane-induced bradykinin generation coupled with ACE-inhibitor induced prolongation of bradykinin half-life. Type A reactions occur in a reuse setting, alos, and these may be related to some as yet poorly understood interaction between bleach, reuse sterilants, and certain dialyzer membranes, again, with ACE inhibitors playing an amplifier role. There is no compelling evidence linking membrane-induced complement activation to type A dialyzer reactions. However, there is a large body of evidence in animal models that exposure to complement fragment-releasing membranes can increase the pulmonary artery pressure and increase thromboxane formation. Thus, at least in principle, a case can be made for using unsubstituted cellulose membranes with caution in patients with a history of atopy or eosinophilia, particularly if acetate dialysate is to be used. Such a caution, however, must be viewed as conjectural in the absence of definitive evidence. Type B dialyzer reactions (mild back and chest pain 20-60 min into the dialysis session) is a phenomenon that is in the process of vanishing. The reason why is unclear. These reactions may have been due to some sort of dialyzer contaminant, or they may have been due to complement fragment release and required the use of acetate dialysate as a cofactor. In any event, recent well designed studies fail to find any differences in symptoms between unsubstituted cellulose and synthetic membranes. Membrane-induced complement fragment release also may play a minor role in dialysis hypoxemia, but evidence is conflicting in this area. Again, the use of acetate dialysate appears to be an important cofactor. Post-dialysis events which may be conceivably linked to the delayed effects of complement fragment releasing membranes need to be evaluated in controlled studies. Studies suggesting increased post-dialysis catabolism with use of unsubstituted cellulose membranes need to be confirmed in dialysis patients, and symptomatic correlates should be sought and evaluated.

Anaphylaxis↗
PubMed1993

Linear estimates of variable-volume, single-pool Kt/V: an analysis of error.

Two linear approximations of variable-volume, single-pool Kt/V were compared. Each is based on the corrected postserum/preserum urea nitrogen ratio (R), called R', where R' = R - 0.03 - UF/W (UF/W being the ratio of the ultrafiltrate volume removed to the postdialysis weight). The two formulas were derived by construction of tangents to the exponential curve y = -In(R') at approximately 1.0 and 1.3, namely, y = 2 - 2.7(R') and y = 2.2 - 3.3(R'), respectively. The linear formulas were compared with each other and to our previous logarithmic formula -In(R - 0.008*t - UF/W). All were compared with the modeled Kt/V using a variable-volume, single-pool kinetic model in 500 dialysis sessions, with Kt/V ranging from 0.7 to 2.1. Analysis of error uncovered systematic errors in all the formulas. However, each of the new linear formulas had very little systematic error in the Kt/V range it was designed for, over a span of 0.6 - 0.7 Kt/V units. Outside this range the linear formulas underestimate the variable-volume, single-pool modeled Kt/V, but, barring two-pool or other technical errors, they do not markedly overestimate Kt/V in any Kt/V range. The total error with the new linear formulas was an acceptable 5%, in the range they were designed for. The results suggest that precise estimates of Kt/V can be derived using linear formulas as long as a given Kt/V range is targeted.

Blood Urea Nitrogen↗
PubMed1993

Cytosolic free calcium regulation in response to acute changes in intracellular pH in vascular smooth muscle.

This study examined the mechanisms whereby alterations of intracellular pH (pHi) impact on free cytosolic calcium (Cai2+) in cultured rat aortic vascular smooth muscle cells (VSMC) assayed in the presence of HCO3/CO2. Rapid cell alkalinization, effected by the exposure to NH4Cl or removal of CO2 from the superfusate, produced a rapid increase in Cai2+. The rise in Cai2+ was markedly diminished when sarcoplasmic reticulum (SR) Ca2+ stores had been depleted by prior exposure to arginine vasopressin (AVP) in Ca(2+)-free media or when SR release and reuptake of Ca2+ were blocked by the addition of 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), but was unaffected by the removal of external Ca2+ or inhibition of Ca2+ entry using NiCl2. Cell acidification also resulted in a rapid increase in Cai2+. This Cai2+ increase was most apparent when pHi was very low (< 6.6) and was unaffected by removal of external Ca2+ or NiCl2 addition. Unlike the effect of cell alkalinization, the increase in Cai2+ associated with cell acidification was not prevented by pretreatment with AVP or TMB-8. We conclude that, in cultured VSMC, acute intracellular alkalinization and, to a lesser extent, acidification result in release of Ca2+ from internal stores. Alkalinization increases Cai2+ by promoting its release from a store which is AVP and TMB-8 sensitive, most likely the SR. Cell acidification increases Cai2+ from an intracellular store(s) that is neither AVP nor TMB-8 sensitive. The increase in Cai2+ produced by cell acidification may be explained on the basis of cell buffering such that, as cytosolic H+ increases, it displaces Cai2+ from internal buffers with similar affinities for Ca2+ and H+.

Ammonium Chloride↗