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Nicholas F LaRusso

Publications and source records attributed to Nicholas F LaRusso.

47 records · Page 3Linked to original sources
PubMed2002

Expression and localization of aquaporin water channels in rat hepatocytes. Evidence for a role in canalicular bile secretion.

Although bile formation requires that large volumes of water be rapidly transported across liver epithelia, including hepatocytes, the molecular mechanisms by which water is secreted into bile are obscure. The aquaporins are a family of 10 channel-forming, integral membrane proteins of approximately 28 kDa numbered 0-9 that allow water to rapidly traverse epithelial barriers in several organs including kidney, eye, and brain. We found transcripts of three of 10 aquaporins in hepatocytes (aquaporin 8 aquaporin 9 > aquaporin 0) by reverse transcription-polymerase chain reaction and quantitative ribonuclease protection assays; immunohistochemistry confirmed the presence of these three proteins in liver. Immunoblots of subcellular fractions of hepatocytes showed enrichment of aquaporins 0 and 8 in microsomes and canalicular plasma membranes; aquaporin 9 was enriched only in basolateral plasma membranes. Immunofluorescence of hepatocyte couplets confirmed the intracellular/canalicular localization of aquaporins 0 and 8 and the basolateral localization of aquaporin 9. Upon exposure of couplets to a choleretic stimulus (i.e. dibutyryl cAMP), aquaporin 8 redistributed to the canalicular plasma membrane; the subcellular distributions of aquaporins 0 and 9 were unaffected. In addition, exposure of couplets to dibutyryl cAMP caused an increase in canalicular water transport in the presence and absence of an osmotic gradient, an effect that was blocked by aquaporin inhibitors. These results provide evidence that aquaporins are present in hepatocytes and that aquaporins are involved in agonist-stimulated canalicular bile secretion.

Animals↗
PubMed2002

Cryptosporidiosis and the pathogenesis of AIDS-cholangiopathy.

Cryptosporidium, an intracellular parasite that infects the gastrointestinal epithelium and other mucosal surfaces, causes self-limited diarrhea in immunocompetent subjects and potentially life-threatening syndromes in immunocompromised individuals, primarily those with acquired immunodeficiency syndrome (AIDS). Cryptosporidium is also the single most common identifiable pathogen in the biliary tract in patients with AIDS-cholangiopathy, an important biliary disorder caused by opportunistic infection of the biliary epithelium and resulting in significant morbidity and mortality in AIDS patients. The organism stimulates periductal inflammation in the biliary tree, induces biliary epithelial cell apoptosis, and thus contributes to the pathogenesis of AIDS-cholangiopathy. Currently, there is no fully effective medical therapy for both of the diseases. A better understanding of the parasitology of Cryptosporidium and the pathophysiology of biliary cryptosporidiosis should aid not only our understanding of the pathogenesis of AIDS-cholangiopathy but also the development of effective therapies and control of this ubiquitous, highly infectious threat.

AIDS-Related Opportunistic Infections↗
PubMed2002

Intrahepatic bile ducts transport water in response to absorbed glucose.

The physiological relevance of the absorption of glucose from bile by cholangiocytes remains unclear. The aim of this study was to test the hypothesis that absorbed glucose drives aquaporin (AQP)-mediated water transport by biliary epithelia and is thus involved in ductal bile formation. Glucose absorption and water transport by biliary epithelia were studied in vitro by microperfusing intrahepatic bile duct units (IBDUs) isolated from rat liver. In a separate set of in vivo experiments, bile flow and absorption of biliary glucose were measured after intraportal infusion of D-glucose or phlorizin. IBDUs absorbed D-glucose in a dose- and phlorizin-dependent manner with an absorption maximum of 92.8 +/- 6.2 pmol. min(-1). mm(-1). Absorption of D-glucose by microperfused IBDUs resulted in an increase of water absorption (J(v) = 3-10 nl. min(-1). mm(-1), P(f) = 40 x 10(-3) cm/sec). Glucose-driven water absorption by IBDUs was inhibited by HgCl(2), suggesting that water passively follows absorbed D-glucose mainly transcellularly via mercury-sensitive AQPs. In vivo studies showed that as the amount of absorbed biliary glucose increased after intraportal infusion of D-glucose, bile flow decreased. In contrast, as the absorption of biliary glucose decreased after phlorizin, bile flow increased. Results support the hypothesis that the physiological significance of the absorption of biliary glucose by cholangiocytes is likely related to regulation of ductal bile formation.

Animals↗
PubMed2002

Channel-mediated water movement across enclosed or perfused mouse intrahepatic bile duct units.

We previously reported the development of reproducible techniques for isolating and perfusing intact intrahepatic bile duct units (IBDUs) from rats. Given the advantages of transgenic and knockout mice for exploring ductal bile formation, we report here the adaptation of those techniques to mice and their initial application to the study of water transport across mouse intrahepatic biliary epithelia. IBDUs were isolated from livers of normal mice by microdissection combined with enzymatic digestion. After culture, isolated IBDUs sealed to form intact, polarized compartments, and a microperfusion system employing those isolated IBDUs developed. A quantitative image analysis technique was used to observe a rapid increase of luminal area when sealed IBDUs were exposed to a series of inward osmotic gradients reflecting net water secretion; the choleretic agonists secretin and forskolin also induced water secretion into IBDUs. The increase of IBDU luminal area induced by inward osmotic gradients and choleretic agonists was reversibly inhibited by HgCl2, a water channel inhibitor. With the use of a quantitative epifluorescence technique in perfused mouse IBDUs, a high osmotic water permeability (P(f) = 2.5-5.6 x 10(-2) cm/s) was found in response to osmotic gradients, further supporting the presence of water channels. These findings suggest that, as in the rat, water transport across intrahepatic biliary epithelia in mice is water channel mediated.

Animals↗
PubMed2002

Experimental models to study cholangiocyte biology.

Cholangiocytes-the epithelial cells which line the bile ducts-are increasingly recognized as important transporting epithelia actively involved in the absorption and secretion of water, ions, and solutes. This recognition is due in part to the recent development of new experimental models. New biologic concepts have emerged including the identification and topography of receptors and flux proteins on the apical and/or basolateral membrane which are involved in the molecular mechanisms of ductal bile secretion. Individually isolated and/or perfused bile duct units from livers of rats and mice serve as new,physiologically relevant in vitro models to study cholangiocyte transport. Biliary tree dimensions and novel insights into anatomic remodeling of proliferating bile ducts have emerged from three-dimensional reconstruction using CT scanning and sophisticated software. Moreover, new pathologic concepts have arisen regarding the interaction of cholangiocytes with pathogens such as Cryptosporidium parvum. These concepts and associated methodologies may provide the framework to develop new therapies for the cholangiopathies, a group of important hepatobiliary diseases in which cholangiocytes are the target cell.

Animals↗
PubMedDate not supplied

Optimization of a research web environment for academic internal medicine faculty.

Usability evaluations are a powerful tool that can assist developers in their efforts to optimize the quality of their web environment. This underutilized, experimental method can serve to move applications toward true user-centered design. This article describes the usability methodology and illustrates its importance and application by describing a usability study undertaken at the Mayo Clinic for the purpose of improving an academic research web environment. Academic institutions struggling in an era of declining reimbursements are finding it difficult to maintain academic enterprises on the back of clinical revenues. This may result in declining amounts of time that clinical investigators have to spend in non-patient-related activities. For this reason, we have undertaken to design a web environment, which can minimize the time that a clinician-investigator needs to spend to accomplish academic instrumental activities of daily living. Usability evaluation is a powerful application of human factors engineering, which can improve the utility of web-based Informatics applications.

Computer Simulation↗