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Biomedical subjects

M H Nathanson

Publications and source records attributed to M H Nathanson.

At least 37 records · Page 2Linked to original sources
PubMed1998

Novel paracrine signaling mechanism in the ocular ciliary epithelium.

The ciliary body contains an epithelial bilayer consisting of an outer pigmented cell layer (PE) and an inner nonpigmented cell layer (NPE) responsible for aqueous humor secretion. Secretion may be mediated in part by cytosolic Ca2+ concentration ([Ca2+]i), but whether or how the two layers could coordinate their Ca2+ signals to regulate secretion is unclear. To investigate interactions between PE and NPE, we examined [Ca2+]i signaling in isolated intact ciliary epithelial bilayers using confocal microscopy. Phenylephrine selectively increased [Ca2+]i in PE and acetylcholine increased [Ca2+]i in NPE, but epinephrine increased [Ca2+]i in both layers. This increase spread from PE to NPE, and [Ca2+]i signaling across the bilayer remained coordinated during [Ca2+]i oscillations. All epinephrine-induced [Ca2+]i signaling was blocked by the alpha1-adrenergic antagonist prazosin, whereas signaling in the NPE but not PE was blocked by the beta-adrenergic antagonist propranolol, the gap junction blockers octanol and 18alpha-glycyrrhetinic acid, or the A kinase inhibitor Rp diastereomer of adenosine 3',5'-cyclic monophosphothioate. The beta-adrenergic agonist isoproterenol failed to increase Ca2+ by itself, but isoproterenol plus phenylephrine-induced [Ca2+]i signals across the bilayer similar to those induced by epinephrine. Finally, isoproterenol increased cell-to-cell spread of lucifer yellow via gap junctions, whereas cell-to-cell spread of [Ca2+]i signals could be induced by photorelease of caged inositol 1,4,5-trisphosphate. Thus, calcium signals are coordinated in the epithelial bilayer so that adrenergic stimulation can increase [Ca2+]i in NPE, but only if NPE are primed by activation of endogenous adenylyl cyclase, whereupon they receive stimulation from adjacent PE via gap junctions. This novel interplay between endocrine and paracrine pathways may coordinate [Ca2+]i signaling across the ciliary epithelial bilayer.

Animals↗
PubMed1998

Stimulation of bile duct epithelial secretion by glybenclamide in normal and cholestatic rat liver.

Cholestasis is a cardinal complication of liver disease, but most treatments are merely supportive. Here we report that the sulfonylurea glybenclamide potently stimulates bile flow and bicarbonate excretion in the isolated perfused rat liver. Video-microscopic studies of isolated hepatocyte couplets and isolated bile duct segments show that this stimulatory effect occurs at the level of the bile duct epithelium, rather than through hepatocytes. Measurements of cAMP, cytosolic pH, and Ca2+ in isolated bile duct cells suggest that glybenclamide directly activates Na+-K+-2Cl- cotransport, rather than other transporters or conventional second-messenger systems that link to secretory pathways in these cells. Finally, studies in livers from rats with endotoxin- or estrogen-induced cholestasis show that glybenclamide retains its stimulatory effects on bile flow and bicarbonate excretion even under these conditions. These findings suggest that bile duct epithelia may represent an important new therapeutic target for treatment of cholestatic disorders.

Animals↗
PubMed1998

The peri-operative management of atrial fibrillation.

Atrial fibrillation is a common arrhythmia frequently seen in surgical patients. The onset of new atrial fibrillation during the peri-operative period is less common. There are many possible precipitating factors, although volatile agents themselves may have an antifibrillatory action. The management of atrial fibrillation includes removal of any precipitating factors and treatment of the arrhythmia itself. Immediate management of acute-onset atrial fibrillation is usually direct current cardioversion. Alternatively, anti-arrhythmic drugs can be used to achieve cardioversion. In patients with rapid, chronic atrial fibrillation or those refractory to cardioversion, priority is given to control of the ventricular rate. Thrombo-embolism is a significant risk if atrial fibrillation is paroxysmal or persists for more than 48 h.

Anti-Arrhythmia Agents↗
PubMed1998

Volatile versus intravenous anaesthetic techniques for ambulatory anaesthesia.

This review considers the role played by volatile and intravenous agents in the induction and maintenance of anaesthesia for ambulatory surgery. The speed and ease of induction, maintenance and recovery, and associated advantages such as the facilitation of airway manoeuvres, side-effect profiles and economic influences are considered.

Journal Article↗
PubMed1998

Telenzepine-sensitive muscarinic receptors on rat pancreatic acinar cells.

To identify the muscarinic subtype present on the rat pancreatic acinar cell, we examined the effects of different muscarinic receptor antagonists on amylase secretion and proteolytic zymogen processing in isolated rat pancreatic acini. Maximal zymogen processing required a concentration of carbachol 10- to 100-fold greater (10(-3) M) than that required for maximal amylase secretion (10(-5) M). Although both secretion and conversion were inhibited by the M3 antagonist 4-diphenylacetoxy-N-methyl-piperidine (4-DAMP) (50% inhibition approximately 6 x 10(-7) M and 1 x 10(-8) M, respectively), the most potent inhibitor was the M1 antagonist telenzepine (50% inhibition approximately 5 x 10(-10) M and 1 x 10(-11) M, respectively). Pirenzepine, another M1 antagonist, and the M2 antagonist methoctramine did not reduce amylase secretion or zymogen processing in concentrations up to 1 x 10(-5) M. Analysis of acinar cell muscarinic receptor by PCR revealed expression of both m1 and m3 subtypes. The pancreatic acinar cell has a distinct pattern of muscarinic antagonist sensitivity (telenzepine >> 4-DAMP > pirenzepine) with respect to both amylase secretion and zymogen conversion.

Animals↗
PubMed1997

Mechanism of long-range Ca2+ signalling in the nucleus of isolated rat hepatocytes.

Ca2+ regulates a wide range of cell proteins, in both the cytosol and nucleus. It enters the nucleus from stores along the nuclear envelope, but how it then spreads through the nuclear interior is unknown. Here we used high-speed confocal line-scanning microscopy to examine the propagation of Ca2+ waves across nuclei in isolated rat hepatocytes. Nuclear Ca2+ waves began at the nucleus/cytosol border as expected, then spread across the nucleus at less than half the speed of cytosolic Ca2+ waves. High concentrations of caffeine slowed Ca2+ waves in the cytosol but not in the nucleus. We developed a mathematical model based on diffusion to analyse these data, and the model was able to describe the nuclear but not cytosolic Ca2+ waves that were experimentally observed. These findings suggest that Ca2+ waves cross the nucleus by simple diffusion, which is distinct from the reaction-diffusion mechanism by which Ca2+ waves propagate across the cytosol. Since the range of messenger action for Ca2+ in the cytosol is much smaller than the distance across the nucleus, this also suggests that the unique environment and geometry of the nuclear interior may permit this simple mechanism of Ca2+ wave propagation to control Ca2+-mediated processes in a relatively large region despite Ca2+ release pools that are spatially limited.

Animals↗
PubMed1997

Nitric oxide donors stimulate bile flow and glutathione disulfide excretion independent of guanosine 3',5'-cyclic [corrected] monophosphate in the isolated perfused rat liver.

Nitric oxide (NO) modulates several metabolic functions in hepatocytes, but the role of NO in bile secretion has not been clearly defined. In the present study, we examined the effects of NO on bile flow and biliary HC03- and glutathione excretion in the isolated perfused rat liver and assessed the role of guanosine 3',5'-cyclic monophosphate (cGMP) in mediating these effects. The NO donors sodium nitroprusside (SNP) and S-nitroso-acetyl-penicillamine stimulated bile flow and increased both HCO3- and glutathione excretion. Increases in bile flow were linearly related to increases in biliary glutathione concentration and output (P < .0001), which were almost entirely caused by glutathione disulfide, whereas the excretion of reduced glutathione remained unchanged. NO donors increased cGMP concentrations in bile and perfusate, and the membrane-permeant cGMP analogue dibutyryl cGMP was also found to stimulate bile flow and HCO3- excretion. However, in contrast to the NO donors, dibutyryl cGMP did not increase glutathione excretion. Furthermore, the NO donors failed to stimulate bile flow in mutant TR- rats in which the canalicular transport of glutathione and glutathione conjugates is deficient, although dibutyryl cGMP increased bile flow and HCO3- excretion in the mutant rats as in normals. These findings indicate that exogenous sources of NO increase bile acid-independent bile flow by stimulating glutathione disulfide excretion, effects that are independent of cGMP.

Animals↗
PubMed1997

Endotoxin impairs biliary glutathione and HCO3- excretion and blocks the choleretic effect of nitric oxide in rat liver.

Cholestasis in patients with sepsis has been attributed to the effects of endotoxin (lipopolysaccharides, LPS) and LPS-induced cytokines, which are also potent stimulators of systemic and hepatic nitric oxide (NO) synthesis. NO donors stimulate bile acid-independent bile flow in normal rat liver, but the effects of LPS-induced NO on bile formation remain unclear. To address this question we examined the effects of NO and its mediator guanosine 3',5'-cyclic monophosphate (cGMP) on bile flow and biliary HCO3- and glutathione excretion in isolated perfused rat livers (IPRL) from LPS-treated rats. Portal and systemic NO2- + NO3- plasma levels were increased 47-fold in LPS-treated rats and were also elevated in perfusate (6-fold) and bile (9-fold) after isolating and perfusing livers from these animals. Bile flow, HCO3-, and glutathione output were decreased by 33%, 25%, and 81% in these IPRL, respectively. Stimulation of NO synthesis with L-arginine or inhibition of inducible NO synthesis with aminoguanidine did not change bile flow, although pretreatment with aminoguanidine inhibited NO production by 85%. Moreover, the choleretic effects of infusions of the NO donors sodium nitroprusside (SNP) and S-nitroso-acetyl-penicillamine were markedly reduced in endotoxemic IPRL compared with normal controls, and SNP-induced HCO3- and glutathione excretion were reduced by 61% and 86%, respectively. SNP-induced cyclic GMP production was 2.3-fold lower than in normals, but the choleretic effect of dibutyryl cGMP was only slightly reduced in endotoxemic livers. These findings indicate that LPS reduces bile acid-independent bile flow primarily by inhibiting biliary excretion of glutathione and to a lesser extent HCO3-, whereas LPS-induced NO does not modulate bile formation in endotoxemia. Thus, impairment of the major determinants of bile acid-independent bile flow by LPS may contribute significantly to the pathogenesis of the cholestasis of sepsis.

Animals↗
PubMed1996

Isolated rat hepatocytes can signal to other hepatocytes and bile duct cells by release of nucleotides.

Intercellular communication among certain cell types can occur via ATP secretion, which leads to stimulation of nucleotide receptors on target cells. In epithelial cells, however, intercellular communication is thought to occur instead via gap junctions. Here we examined whether one epithelial cell type, hepatocytes, can also communicate via nucleotide secretion. The effects on cytosolic Ca2+ ([Ca2+]i) of mechanical stimulation, including microinjection, were examined in isolated rat hepatocytes and in isolated bile duct units using confocal fluorescence video microscopy. Mechanical stimulation of a single hepatocyte evoked an increase in [Ca2+]i in the stimulated cell plus an unexpected [Ca2+]i rise in neighboring noncontacting hepatocytes. Perifusion with ATP before mechanical stimulation suppressed the [Ca2+]i increase, but pretreatment with phenylephrine did not. The P2 receptor antagonist suramin inhibited these intercellular [Ca2+]i signals. The ATP/ADPase apyrase reversibly inhibited the [Ca2+]i rise induced by mechanical stimulation, and did not block vasopressin-induced [Ca2+]i signals. Mechanical stimulation of hepatocytes also induced a [Ca2+]i increase in cocultured isolated bile duct units, and this [Ca2+]i increase was inhibited by apyrase as well. Finally, this form of [Ca2+]i signaling could be elicited in the presence of propidium iodide without nuclear labeling by that dye, indicating that this phenomenon does not depend on disruption of the stimulated cell. Thus, mechanical stimulation of isolated hepatocytes, including by microinjection, can evoke [Ca2+]i signals in the stimulated cell as well as in neighboring noncontacting hepatocytes and bile duct epithelia. This signaling is mediated by release of ATP or other nucleotides into the extracellular space. This is an important technical consideration given the widespread use of microinjection techniques for examining mechanisms of signal transduction. Moreover, the evidence provided suggests a novel paracrine signaling pathway for epithelia, which previously were thought to communicate exclusively via gap junctions.

Adenosine Triphosphate↗
PubMed1996

Preventing pain during injection of propofol: the optimal dose of lidocaine.

STUDY OBJECTIVE: To define the optimal dose of lidocaine to be added to propofol to reduce the incidence of pain during its injection. DESIGN: Double-blind, randomized, placebo-controlled study. SETTING: Medical center operating rooms. PATIENTS: 135 ASA I and II female patients undergoing minor outpatient surgery. INTERVENTIONS: Patients were randomly allocated to one of five groups: Group A (control), no lidocaine: Group B, lidocaine 10 mg: Group C, lidocaine 20 mg; Group D, lidocaine 30 mg; Group F, lidocaine 40 mg. For each patient, pain during injection of the propofol solution was graded as none, mild, moderate, or severe. MEASUREMENTS AND MAIN RESULTS: The incidence of pain in the control group was 85%. All treatment groups receiving lidocaine had a significantly lower incidence of pain compared with the control group (P < 0.001). The lidocaine 30 mg and 40 mg groups both had a 7% incidence of pain, which was significantly less than a 33% incidence in the lidocaine 10 mg group (P < 0.05). CONCLUSIONS: Within this dose range and in this patient population, 30 mg of lidocaine is optimal for reducing the pain during injection of propofol.

Adult↗
PubMed1996

Prevention of pain on injection of propofol: a comparison of lidocaine with alfentanil.

We undertook a randomized, placebo-controlled, double-blind study to compare the use of alfentanil 1 mg and lidocaine 40 mg for the reduction of pain during injection of propofol. Eighty-nine patients were randomly allocated to one of three groups: Group L, lidocaine 40 mg added to 180 mg propofol; Group A, alfentanil 1 mg 30 s prior to propofol; or Group P, placebo (normal saline). The incidence of pain in the placebo group was 67%. Both treatment groups had a significantly lower incidence of pain than the placebo group (P < 0.002). There was no significant difference in the incidence of pain between the groups receiving lidocaine or alfentanil (13% and 24%, respectively). There was no significant difference in the induction dose of propofol between the groups. Fifty-two percent of patients who experienced pain at induction had recall of that pain in the recovery room. Alfentanil 1 mg and lidocaine 40 mg are both effective in reducing pain during injection of propofol.

Adolescent↗
PubMed1996

Characterization of cytosolic Ca2+ signaling in rat bile duct epithelia.

Bile duct epithelia play an important role in the formation and conditioning of bile. However, hormonal responses in this epithelial tissue are incompletely understood. Secretin increases ductular secretion through the intracellular messenger adenosine 3',5'-cyclic monophosphate (cAMP), but whether hormones increase cytosolic Ca2+ (Ca2+(i)) in these cells and whether Ca2+(i) regulates duct secretion is unknown. To address these questions, we examined Ca2+(i) signaling in isolated rat bile duct units using ratio microspectrofluorometry and confocal microscopy. We also used videomicroscopy to examine secretion and cell volume in isolated bile duct cells and duct units. Acetylcholine (ACh) and ATP both increased Ca2+(i) in bile duct units and elicited patterns of Ca2+(i) increases and oscillations that were distinct and dose dependent. In contrast, Ca2+(i) was not increased by the hepatocyte Ca2+(i) agonists vasopressin, angiotensin, and phenylephrine or by the exocrine pancreas agonists cholecystokinin (CCK) and bombesin. In addition, secretin did not increase Ca2+(i) in the isolated bile duct units, whereas ACh did not increase Ca2+(i) in isolated hepatocytes. Mobilization of internal, thapsigargin-sensitive Ca2+ stores contributed more than influx of extracellular Ca2+ to the Ca2+(i) increases induced in the duct units, and ATP-induced increases in Ca2+(i) could be blocked by microinjection of heparin but not de-N-sulfated heparin. ACh transiently decreased bile flow in the isolated perfused rat liver, although neither ACh nor ATP altered secretion in isolated ducts or changed the volume of single isolated bile duct cells. These findings demonstrate that bile duct epithelial cells possess both muscarinic and purinergic receptors that activate Ca2+(i) signaling pathways similar to those seen in other types of epithelia, but that the two types of receptors elicit distinct patterns of Ca2+(i) signals. Increases in Ca2+(i) have minimal direct effects on bile duct secretion, although it remains to be determined whether such signals selectively modulate other aspects of bile duct epithelial cell function.

Acetylcholine↗
PubMed1996

Characterization and function of ATP receptors on hepatocytes from the little skate Raja erinacea.

Hormonal regulation of hepatocytes, via cytosolic Ca2+ signaling, is well established in higher life forms but has not been investigated in elasmobranchs. We therefore examined Ca2+ signaling in hepatocytes isolated from the little skate, Raja erinacea. In hepatocyte populations, ATP induced a rapid, biphasic increase in Ca2+, as it does in mammalian hepatocytes. Other hormones that act on mammalian hepatocytes, such as vasopressin, angiotensin, and phenylephrine, induced no such Ca2+ increase. The initial phase of the ATP-induced Ca2+ increase was seen even in Ca(2+)-free medium, whereas the late sustained phase of the increase was not. Similar dose-response curves were obtained by stimulation with ATP, ADP, UTP, and 2-methylthio-ATP. In contrast, AMP, adenosine, beta, gamma-methyl-ATP, CTP, and GTP induced little or no Ca2+ increase. In single hepatocytes, ATP, ADP, UTP, and 2-methylthio-ATP each induced a sustained increase in Ca2+ at high concentrations, but at low concentrations induced Ca2+ oscillations. A maximal concentration of ATP (100 microM) caused a marked, transient increase in bile flow in the isolated perfused skate liver, whereas 100 microM adenosine had no such effect. These findings demonstrate that skate hepatocytes possess P2 nucleotide receptors that link to intracellular plus extracellular Ca2+ mobilization, which in turn regulates bile secretion. The broad specificity of the response to ATP and related compounds suggests either that multiple types of P2 receptors are expressed by skate hepatocytes or else that these cells possess a single primitive nucleotide receptor from which other P2 subtypes subsequently evolved.

Animals↗
PubMed1996

A midregion parathyroid hormone-related peptide mobilizes cytosolic calcium and stimulates formation of inositol trisphosphate in a squamous carcinoma cell line.

A midregion fragment of PTH-related protein (PTHrP), which is intensively conserved across species, has been identified as a secretory product of several different cell types, including keratinocytes and squamous carcinomas. As recent data suggest that a midregion PTHrP fragment may be biologically active, we hypothesized that midregion PTHrPs interact with unique cell surface receptors that mediate autocrine or paracrine action. Dose-dependent transient elevations in intracellular calcium ([Ca2-]i) were observed in fura-2-loaded SqCC/Y1 squamous carcinoma cells exposed to human (h) PTHrP-(67-86)NH2, [Tyr36]hPTHrP-(1-36)NH2, and hPTHrP-(1-141) at concentrations ranging from 1 pM to 1 microM. The effects of maximal stimulatory concentrations of [Tyr36]PTHrP-(1-36)NH2 and PTHrP-(67-86)NH2 on [Ca2+]i were additive. The inhibitory PTH analog, [D-Trp12,Tyr34]bovine PTH-(7-34)NH2, attenuated the [Ca2+]i response to [Tyr36]hPTHrP-(1-36)NH2, but not that to PTHrP-(67-86)NH2. These data suggest that PTHrP-(67-86)NH2 activates a different receptor pathway in SqCC/Y1 cells from the one activated by [Tyr36]hPTHrP-(1-36)NH2. Radiolabeled PTHrP-(67-86)NH2 did not bind to SqCC/Y1 cells, and PTHrP-(67-86)NH2 did not compete for binding of 125I-labeled [Tyr36]PTHrP-(1-36)NH2 to PTH/PTHrP receptors on SaOS-2 osteosarcoma cells. Activation of the phospholipase C pathway by PTHrP-(67-86)NH2 was confirmed by exposing SqCC/Y1 cells to peptide for 1 min and measuring the accumulation of inositol trisphosphates. PTHrP-(67-86)NH2 treatment (100 nM) resulted in maximal stimulation of inositol trisphosphates of 3.1 +/- 0.1-fold over the control value, with an EC50 of 1.5 +/- 1.2 nm. In contrast, PTHrP-(67-86)NH2 (0.1 nM to 1 microM) did not stimulate adenylyl cyclase in SqCC/Y1 cells despite vigorous stimulation of cAMP formation by isoproterenol (1 microM) to 66-fold over the basal value. To determine whether messenger RNA (mRNA) prepared from SqCC/Y1 cells would direct the translation of a receptor protein that mediated a [Ca2+]i response to PTHrP-(67-86)NH2, we performed expression studies in Xenopus oocytes. Fluo-3 fluorescence in Xenopus oocytes expressing SqCC/Y1 mRNA was visualized by confocal video microscopy after exposure to 1 microM PTHrP-(67-86)NH2. Clear increases in [Ca2+]i were detected in mRNA-injected, but not in sham-injected, oocytes. Finally, we examined the effect of PTHrP-(67-86)NH2 treatment on fibronectin secretion from SqCC/YN1 cells. A significant 3.5-fold increase in fibronectin secretion into conditioned medium was observed when SqCC/Y1 cells were exposed to 100 nM PTHrP-(67-86)NH2, and this effect was dose dependent, with an EC50 of 0.1 nM. We conclude that PTHrP-(67-86)NH2 activates phospholipase C-dependent pathways in SqCC/Y1 cells through a receptor distinct from that activated by PTHrP-(1-36) in the same cells. As a midregion secretory fragment of PTHrP has been partially purified from several different cell types, this receptor may have broad biological significance.

Animals↗