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Alpha-1-antitrypsin deficiency is a relatively common but under-recognized genetic disease in which individuals homozygous for the mutant Z disease-associated allele are at risk for the development of liver disease and emphysema. The protein product of the mutant Z gene is synthesized in hepatocytes but accumulates intracellularly rather than being appropriately secreted. The downstream effects of the intracellular accumulation of the mutant Z protein include the formation of unique protein polymers, activation of autophagy, mitochondrial injury, endoplasmic reticulum stress, and caspase activation, which subsequently progress in a cascade, causing chronic hepatocellular injury. The variable clinical presentations among affected individuals suggest an important contribution of genetic and environmental disease modifiers, which are only now being identified. The heterozygous carrier state for the mutant Z gene, found in 1.5% to 3% of the population, is not itself a common cause of liver injury but may be a modifier gene for other liver diseases.

Alpha-1-antitrypsin (alpha1AT) deficiency in its most common form is caused by homozygosity for the alpha1AT mutant Z gene. This gene encodes a mutant Z secretory protein, primarily synthesized in the liver, that assumes an abnormal conformation and accumulates within hepatocytes causing liver cell injury. Studies have shown that mutant alpha1ATZ protein molecules form unique protein polymers. These Z protein polymers have been hypothesized to play a critical role in the pathophysiology of liver injury in this disease, although a lack of quantitative methods to isolate the polymers from whole liver has hampered further analysis. In this study, we demonstrate a quantitative alpha1ATZ polymer isolation technique from whole liver and show that the hepatocellular periodic acid-Schiff-positive globular inclusions that are the histopathological hallmark of this disease are composed almost entirely of the polymerized alpha1ATZ protein. Furthermore, we examine the previously proposed but untested hypothesis that induction of alpha1ATZ polymerization by the heat of physiological fever is part of the mechanism of hepatic alpha1ATZ protein accumulation. The results, however, show that fever-range temperature elevations have no detectable effect on steady-state levels of intrahepatic Z protein polymer in a model in vivo system. In conclusion, methods to separate insoluble protein aggregates from liver can be used for quantitative isolation of alpha1ATZ protein polymers, and the effect of heat from physiological fever may be different in vivo compared with in vitro systems.

We have developed a mathematical model of the rabbit atrial myocyte and have used it in an examination of the ionic basis of the atrial action potential. Available biophysical data have been incorporated into the model to quantify the specific ultrastructural morphology, intracellular ion buffering, and time- and voltage-dependent currents and transport mechanisms of the rabbit atrial cell. When possible, mathematical expressions describing ionic currents identified in rabbit atrium are based on whole cell voltage-clamp data from enzymatically isolated rabbit atrial myocytes. This membrane model is coupled to equations describing Na+, K+, and Ca2+ homeostasis, including the uptake and release of Ca2+ by the sarcoplasmic reticulum and Ca2+ buffering. The resulting formulation can accurately simulate the whole cell voltage-clamp data on which it is based and provides fits to a family of rabbit atrial cell action potentials obtained at 35 degrees C over a range of stimulus rates (0.2–3.0 Hz). The model is utilized to provide a qualitative prediction of the intracellular Ca2+ concentration transient during the action potential and to illustrate the interactions between membrane currents that underlie repolarization in the rabbit atrial myocyte.

Objectives To prospectively assess the value of serum total bilirubin (TB) within 3 months of hepatoportoenterostomy (HPE) in infants with biliary atresia as a biomarker predictive of clinical sequelae of liver disease in the first 2 years of life. Study design Infants with biliary atresia undergoing HPE between June 2004 and January 2011 were enrolled in a prospective, multicenter study. Complications were monitored until 2 years of age or the earliest of liver transplantation (LT), death, or study withdrawal. TB below 2 mg/dL (34.2 μM) at any time in the first 3 months (TB Results Fifty percent (68/137) of infants had TB P P P P P = .0002), LT (OR 12.4, 95% CI 5.3-28.7, P P Conclusions Infants whose TB does not fall below 2.0 mg/dL within 3 months of HPE were at high risk for early disease progression, suggesting they should be considered for LT in a timely fashion. Interventions increasing the likelihood of achieving TB Trial registration ClinicalTrials.gov: NCT00061828 and NCT00294684.

Alpha-1-antitrypsin (alpha1AT) deficiency in its most common form is caused by homozygosity for the alpha1AT mutant Z gene. This gene encodes a mutant Z secretory protein, primarily synthesized in the liver, that assumes an abnormal conformation and accumulates within hepatocytes causing liver cell injury. Studies have shown that mutant alpha1ATZ protein molecules form unique protein polymers. These Z protein polymers have been hypothesized to play a critical role in the pathophysiology of liver injury in this disease, although a lack of quantitative methods to isolate the polymers from whole liver has hampered further analysis. In this study, we demonstrate a quantitative alpha1ATZ polymer isolation technique from whole liver and show that the hepatocellular periodic acid-Schiff-positive globular inclusions that are the histopathological hallmark of this disease are composed almost entirely of the polymerized alpha1ATZ protein. Furthermore, we examine the previously proposed but untested hypothesis that induction of alpha1ATZ polymerization by the heat of physiological fever is part of the mechanism of hepatic alpha1ATZ protein accumulation. The results, however, show that fever-range temperature elevations have no detectable effect on steady-state levels of intrahepatic Z protein polymer in a model in vivo system. In conclusion, methods to separate insoluble protein aggregates from liver can be used for quantitative isolation of alpha1ATZ protein polymers, and the effect of heat from physiological fever may be different in vivo compared with in vitro systems.

We have developed a mathematical model of the electrophysiological responses in a single cell from the adult, human atrium, based on action potential and voltage clamp data recorded at 33/spl deg/C. Our formulation consists of two closely interacting parts a Hodgkin-Huxley (HH) membrane equivalent circuit model for the sarcolemma, and a fluid compartment model for the intracellular medium. These simulations produce acceptable fits to experimentally recorded action potential data, and can therefore be used to gain insight into how the ionic currents interact during the action potential in human atrial cells.

Abstract —We have developed a mathematical model of the human atrial myocyte based on averaged voltage-clamp data recorded from isolated single myocytes. Our model consists of a Hodgkin-Huxley–type equivalent circuit for the sarcolemma, coupled with a fluid compartment model, which accounts for changes in ionic concentrations in the cytoplasm as well as in the sarcoplasmic reticulum. This formulation can reconstruct action potential data that are representative of recordings from a majority of human atrial cells in our laboratory and therefore provides a biophysically based account of the underlying ionic currents. This work is based in part on a previous model of the rabbit atrial myocyte published by our group and was motivated by differences in some of the repolarizing currents between human and rabbit atrium. We have therefore given particular attention to the sustained outward K + current ( I sus ), which putatively has a prominent role in determining the duration of the human atrial action potential. Our results demonstrate that the action potential shape during the peak and plateau phases is determined primarily by transient outward K + current, I sus , and L-type Ca 2+ current ( I Ca,L ) and that the role of I sus in the human atrial action potential can be modulated by the baseline sizes of I Ca,L , I sus , and the rapid delayed rectifier K + current. As a result, our simulations suggest that the functional role of I sus can depend on the physiological/disease state of the cell.

A mathematical model of the electrophysio-logical responses of the rabbit atrial cell has recently been developed by our group that is based on whole-cell voltage clamp data from enzymatically isolated cardiac myocytes. It is able to simulate (1) the whole-cell voltage clamp data upon which it is based, (2) the frequency-dependent action potential waveshape changes that occur in response to variations in the rate of stimulation, and (3) the modulation of frequency-dependent action potential waveshape changes by acetylcholine. The model also predicts the intracellular [Ca2+] i -transient during the action potential and changes that this waveform undergoes as stimulus rate is varied.

We have developed a mathematical model of the rabbit atrial myocyte as a tool to examine the ionic bases underlying rate-dependent changes in action potential waveshape. Such changes have been postulated to result primarily from two causes: (1) incomplete reactivation of ionic currents and (2) rate-dependent changes in ion concentration gradients. The model has incorporated biophysical data to quantify the specific ultrastructural morphology, ion buffering, and sarcolemmal electrophysiology of the rabbit atrial cell. In particular, mathematical forms describing ionic currents identified in rabbit atrium are based on whole-cell voltage-clamp data from enzymatically isolated rabbit cardiomyocytes. We address the rate-dependent effects of incomplete reactivation by accounting for the reactivation timecourse of the largest ionic currents (fast sodium, transient outward, and long-lasting calcium currents) found in rabbit atrium. Modeling simulations are obtained by numerical integration of the relatively stiff system of 28 coupled ordinary differential equations. Our model can simulate (1) the whole-cell voltage-clamp data upon which it is based, (2) the nominal action potential waveshape at a typical, physiological rate of stimulation, and (3) changes in waveshape that occur as the stimulus rate is varied. As changes in early repolarization have been correlated experimentally with alterations in the transient outward current (It), the model offers a semi-quantitative interpretation of the importance of It to rate-dependent waveshape changes. Our model also predicts the intracellular [Ca2+]i-transient that occurs during the action potential. We have utilized our model to examine action potential refractoriness by simulating (1) the reponse elicited by stimulation of a “premature” action potential and (2) the predicted waveshape changes that occur at high rates of cell stimulation. These responses provide insight into the electrophysiological changes that may accompany atrial arrhythmia.