Publications by authors named "Thomas R Murphy"

9 Publications

  • Page 1 of 1

Astrocyte-Selective Volume Increase in Elevated Extracellular Potassium Conditions Is Mediated by the Na/K ATPase and Occurs Independently of Aquaporin 4.

ASN Neuro 2020 Jan-Dec;12:1759091420967152

Center for Glial-Neuronal Interactions, University of California, Riverside, Riverside, United States.

Astrocytes and neurons have been shown to swell across a variety of different conditions, including increases in extracellular potassium concentration (^[K]). The mechanisms involved in the coupling of K influx to water movement into cells leading to cell swelling are not well understood and remain controversial. Here, we set out to determine the effects of ^[K] on rapid volume responses of hippocampal CA1 pyramidal neurons and stratum radiatum astrocytes using real-time confocal volume imaging. First, we found that elevating [K] within a physiological range (to 6.5 mM and 10.5 mM from a baseline of 2.5 mM), and even up to pathological levels (26 mM), produced dose-dependent increases in astrocyte volume, with absolutely no effect on neuronal volume. In the absence of compensating for addition of KCl by removal of an equal amount of NaCl, neurons actually shrank in ^[K], while astrocytes continued to exhibit rapid volume increases. Astrocyte swelling in ^[K] was not dependent on neuronal firing, aquaporin 4, the inwardly rectifying potassium channel Kir 4.1, the sodium bicarbonate cotransporter NBCe1, , or the electroneutral cotransporter, sodium-potassium-chloride cotransporter type 1 (NKCC1), but was significantly attenuated in 1 mM barium chloride (BaCl) and by the Na/K ATPase inhibitor ouabain. Effects of 1 mM BaCl and ouabain applied together were not additive and, together with reports that BaCl can inhibit the NKA at high concentrations, suggests a prominent role for the astrocyte NKA in rapid astrocyte volume increases occurring in ^[K]. These findings carry important implications for understanding mechanisms of cellular edema, regulation of the brain extracellular space, and brain tissue excitability.
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http://dx.doi.org/10.1177/1759091420967152DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7586494PMC
October 2020

A Dose-Ranging Study of Epinephrine Hydrofluroalkane Metered-Dose Inhaler (Primatene MIST) in Subjects with Intermittent or Mild-to-Moderate Persistent Asthma.

J Aerosol Med Pulm Drug Deliv 2020 08 6;33(4):186-193. Epub 2020 Mar 6.

Amphastar Pharmaceuticals, Inc., Rancho Cucamonga, California.

Two sequential single-dose crossover dose-ranging studies were performed to evaluate the clinical efficacy and safety profile of epinephrine hydrofluroalkane (HFA) metered-dose inhaler (MDI) formulation at various doses in subjects with asthma. In these multicenter, multiarm, double-blinded, or evaluator-blinded studies, subjects were randomized to receive the epinephrine HFA (Primatene MIST HFA) MDI medication at doses ranging from 90 to 440 μg/dose, as well as to a placebo (PLA) control and an active control of epinephrine CFC (chlorofluorocarbon) MDI (Primatene MIST CFC) at 220 μg/inhalation. Spirometry testing for FEV1 (Forced Expiratory Volume in one second) demonstrated statistically significant improvements over PLA for epinephrine HFA MDI at all doses above 125 μg, as the amount out of the actuator (i.e., mouthpiece). The efficacy results for epinephrine HFA MDI in the dose range of 125-250 μg were also comparable to epinephrine CFC MDI (220 μg/inh). Safety assessments demonstrated minimal safety concerns for all treatment groups. No notable safety differences were observed between the studied doses of epinephrine HFA MDI and the active control formulation of epinephrine CFC MDI. The findings indicate that epinephrine HFA MDI provided clinically significant bronchodilator efficacy with minimal safety concerns in a dose range of 125-250 μg. These findings confirmed the optimal treatment doses of 125-250 μg that were appropriate for use in longer term 12 and 26 week chronic dosing studies of epinephrine HFA MDI for patients with intermittent or mild to moderate persistent asthma. Clinical trials registration number: NCT01025648.
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http://dx.doi.org/10.1089/jamp.2019.1558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7407001PMC
August 2020

Impact of omalizumab on patient-reported outcomes in chronic idiopathic urticaria: Results from a randomized study (XTEND-CIU).

J Allergy Clin Immunol Pract 2019 Sep - Oct;7(7):2487-2490.e1. Epub 2019 Apr 26.

Bernstein Clinical Research Center and University of Cincinnati, Cincinnati, Ohio.

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http://dx.doi.org/10.1016/j.jaip.2019.04.020DOI Listing
October 2020

Hippocampal and Cortical Pyramidal Neurons Swell in Parallel with Astrocytes during Acute Hypoosmolar Stress.

Front Cell Neurosci 2017 20;11:275. Epub 2017 Sep 20.

Center for Glial-Neuronal Interactions, University of California, RiversideRiverside, CA, United States.

Normal nervous system function is critically dependent on the balance of water and ions in the extracellular space (ECS). Pathological reduction in brain interstitial osmolarity results in osmotically-driven flux of water into cells, causing cellular edema which reduces the ECS and increases neuronal excitability and risk of seizures. Astrocytes are widely considered to be particularly susceptible to cellular edema due to selective expression of the water channel aquaporin-4 (AQP4). The apparent resistance of pyramidal neurons to osmotic swelling has been attributed to lack of functional water channels. In this study we report rapid volume changes in CA1 pyramidal cells in hypoosmolar ACSF (hACSF) that are equivalent to volume changes in astrocytes across a variety of conditions. Astrocyte and neuronal swelling was significant within 1 min of exposure to 17 or 40% hACSF, was rapidly reversible upon return to normosmolar ACSF, and repeatable upon re-exposure to hACSF. Neuronal swelling was not an artifact of patch clamp, occurred deep in tissue, was similar at physiological vs. room temperature, and occurred in both juvenile and adult hippocampal slices. Neuronal swelling was neither inhibited by TTX, nor by antagonists of NMDA or AMPA receptors, suggesting that it was not occurring as a result of excitotoxicity. Surprisingly, genetic deletion of AQP4 did not inhibit, but rather augmented, astrocyte swelling in severe hypoosmolar conditions. Taken together, our results indicate that neurons are not osmoresistant as previously reported, and that osmotic swelling is driven by an AQP4-independent mechanism.
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http://dx.doi.org/10.3389/fncel.2017.00275DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5611379PMC
September 2017

Turning down the volume: Astrocyte volume change in the generation and termination of epileptic seizures.

Neurobiol Dis 2017 Aug 22;104:24-32. Epub 2017 Apr 22.

Center for Glial-Neuronal Interactions; University of California, Riverside, CA 92521, USA; Department of Cell Biology and Neuroscience, University of California, Riverside, CA 92521, USA. Electronic address:

Approximately 1% of the global population suffers from epilepsy, a class of disorders characterized by recurrent and unpredictable seizures. Of these cases roughly one-third are refractory to current antiepileptic drugs, which typically target neuronal excitability directly. The events leading to seizure generation and epileptogenesis remain largely unknown, hindering development of new treatments. Some recent experimental models of epilepsy have provided compelling evidence that glial cells, especially astrocytes, could be central to seizure development. One of the proposed mechanisms for astrocyte involvement in seizures is astrocyte swelling, which may promote pathological neuronal firing and synchrony through reduction of the extracellular space and elevated glutamate concentrations. In this review, we discuss the common conditions under which astrocytes swell, the resultant effects on neural excitability, and how seizure development may ultimately be influenced by these effects.
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http://dx.doi.org/10.1016/j.nbd.2017.04.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522738PMC
August 2017

Astrocyte calcium microdomains are inhibited by bafilomycin A1 and cannot be replicated by low-level Schaffer collateral stimulation in situ.

Cell Calcium 2014 Jan 30;55(1):1-16. Epub 2013 Oct 30.

Graduate Program in Cell, Molecular, and Developmental Biology, University of California-Riverside, Riverside, CA 92521, United States; Undergraduate Major in Neuroscience, University of California-Riverside, Riverside, CA 92521, United States; Neuroscience Graduate Program, University of California-Riverside, Riverside, CA 92521, United States. Electronic address:

Astrocyte Gq GPCR and IP3 receptor-dependent Ca(2+) elevations occur spontaneously in situ and in vivo. These events vary considerably in size, often remaining confined to small territories of astrocyte processes called "microdomains" and sometimes propagating over longer distances that can include the soma. It has remained unclear whether these events are driven by constitutive (basal) GPCR signaling activity, neuronal action potential-dependent or quantal vesicular release, or some combination of these mechanisms. Here, we applied manipulations to increase or inhibit neuronal vesicular neurotransmitter release together with low-level stimulation of Schaffer collaterals in acute mouse hippocampal slices in an effort to determine the mechanisms underlying spontaneous astrocyte Ca(2+) events. We found no significant change in spontaneous microdomain astrocyte Ca(2+) elevations when neuronal action potentials were significantly enhanced or blocked. The astrocyte Ca(2+) activity was also not affected by inhibitors of group I mGluRs. However, blockade of miniature neurotransmitter release using Bafilomycin A1 significantly reduced the frequency of microdomain astrocyte Ca(2+) elevations. We then tested whether astrocyte Ca(2+) microdomains can be evoked by low intensity SC stimulation. Importantly, microdomains could not be reproduced even using single, low intensity pulses to the SCs at a minimum distance from the astrocyte. Evoked astrocyte Ca(2+) responses most often included the cell soma, were reduced by group I mGluR antagonists, and were larger in size compared to spontaneous Ca(2+) microdomains. Overall, our findings suggest that spontaneous microdomain astrocyte Ca(2+) elevations are not driven by neuronal action potentials but require quantal release of neurotransmitter which cannot be replicated by stimulation of Schaffer collaterals.
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http://dx.doi.org/10.1016/j.ceca.2013.10.004DOI Listing
January 2014

Absence of Cx43 selectively from osteocytes enhances responsiveness to mechanical force in mice.

J Orthop Res 2013 Jul 11;31(7):1075-81. Epub 2013 Mar 11.

Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.

The osteocyte network is crucial for the response of bone to mechanical force. Within this network, connexin43 (Cx43) is thought to mediate the communication of osteocytes and osteoblasts among themselves and the exchange of small molecules with the extracellular milieu. Despite recent advances in understanding Cx43 role for the response of bone cells to mechanical stimulation, the contribution of Cx43 specifically in osteocytes to mechanotransduction in vivo is not well-known. We examined the anabolic response to ulnar axial loading of mice lacking Cx43 in osteocytes (Cx43(ΔOt)). Loading induced a greater increase in periosteal bone formation rate in Cx43(ΔOt) mice compared to control littermates, resulting from higher mineralizing surface and enhanced mineral apposition rate. Expression of β-catenin protein, a molecule implicated in mechanotransduction, was higher in bones from Cx43(ΔOt) mice, compared to littermate controls. In addition, MLO-Y4 osteocytic cells knocked-down for Cx43 exhibited higher β-catenin protein expression and enhanced response to mechanical stimulation. These findings suggest that osteocytes lacking Cx43 are "primed" to respond to mechanical stimulation and that absence of Cx43 in osteocytes unleashes bone formation, by a mechanism that might involve accumulation of β-catenin.
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http://dx.doi.org/10.1002/jor.22341DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3663897PMC
July 2013

Activation of protein kinase D1 in mast cells in response to innate, adaptive, and growth factor signals.

J Immunol 2007 Dec;179(11):7876-82

Department of Medicine, Harvard Medical School, and Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, Boston, MA 02115, USA.

Little is known about the serine/threonine kinase protein kinase D (PKD)1 in mast cells. We sought to define ligands that activate PKD1 in mast cells and to begin to address the contributions of this enzyme to mast cell activation induced by diverse agonists. Mouse bone marrow-derived mast cells (BMMC) contained both PKD1 mRNA and immunoreactive PKD1 protein. Activation of BMMC through TLR2, Kit, or FcepsilonRI with Pam(3)CSK(4) (palmitoyl-3-cysteine-serine-lysine-4), stem cell factor (SCF), and cross-linked IgE, respectively, induced activation of PKD1, as determined by immunochemical detection of autophosphorylation. Activation of PKD1 was inhibited by the combined PKD1 and protein kinase C (PKC) inhibitor Gö 6976 but not by broad-spectrum PKC inhibitors, including bisindolylmaleimide (Bim) I. Pam(3)CSK(4) and SCF also induced phosphorylation of heat shock protein 27, a known substrate of PKD1, which was also inhibited by Gö 6976 but not Bim I in BMMC. This pattern also extended to activation-induced increases in mRNA encoding the chemokine CCL2 (MCP-1) and release of the protein. In contrast, both pharmacologic agents inhibited exocytosis of beta-hexosaminidase induced by SCF or cross-linked IgE. Our findings establish that stimuli representing innate, adaptive, and growth factor pathways activate PKD1 in mast cells. In contrast with certain other cell types, activation of PKD1 in BMMC is largely independent of PKC activation. Furthermore, our findings also indicate that PKD1 preferentially influences transcription-dependent production of CCL2, whereas PKC predominantly regulates the rapid exocytosis of preformed secretory granule mediators.
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http://dx.doi.org/10.4049/jimmunol.179.11.7876DOI Listing
December 2007

Occupational asthma: a case of Baker's asthma.

Allergy Asthma Proc 2004 May-Jun;25(3):151-6

Department of Medicine, Harvard Medical School, Division of Rheumatology, Immunology, and Allergy, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.

Asthma is one of the most prominent respiratory diseases worldwide. It is defined by airflow limitation and/or airway hyperresponsiveness and can be exacerbated by a number of environmental allergens. When allergic asthma exacerbations are attributed to stimuli in a particular work environment, then occupational asthma must be considered. Incidence estimates vary, but in 1999 the Surveillance of Work-Related and Occupational Respiratory Disease in the United Kingdom estimated 4293 incident cases of occupational respiratory disease, an increase of 1427 cases over the previous year. Occupational asthma represented 26% of these cases. Baker's asthma is one of the most frequently reported types of occupational asthma in several countries. Diagniostic steps include thorough history, careful exam, and demonstration of functional reversible airflow obstruction. Treatment modalities used for occupational asthma are similar to those used in the management of other forms of asthma, with particular attention to reducing the level of exposure to the inciting allergen.
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March 2005