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Beggs MR, Lee JJ, Busch K, Raza A, Dimke H, Weissgerber P, Engel J, Flockerzi V, Alexander RT. TRPV6 and Ca v1.3 Mediate Distal Small Intestine Calcium Absorption Before Weaning. Cell Mol Gastroenterol Hepatol 2019; 8:625-642. [PMID: 31398491 PMCID: PMC6889763 DOI: 10.1016/j.jcmgh.2019.07.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 07/15/2019] [Accepted: 07/17/2019] [Indexed: 12/12/2022]
Abstract
BACKGROUND & AIMS Intestinal Ca2+ absorption early in life is vital to achieving optimal bone mineralization. The molecular details of intestinal Ca2+ absorption have been defined in adults after peak bone mass is obtained, but they are largely unexplored during development. We sought to delineate the molecular details of transcellular Ca2+ absorption during this critical period. METHODS Expression of small intestinal and renal calcium transport genes was assessed by using quantitative polymerase chain reaction. Net calcium flux across small intestinal segments was measured in Ussing chambers, including after pharmacologic inhibition or genetic manipulation of TRPV6 or Cav1.3 calcium channels. Femurs were analyzed by using micro-computed tomography and histology. RESULTS Net TRPV6-mediated Ca2+ flux across the duodenum was absent in pre-weaned (P14) mice but present after weaning. In contrast, we found significant transcellular Ca2+ absorption in the jejunum at 2 weeks but not 2 months of age. Net jejunal Ca2+ absorption observed at P14 was not present in either Trpv6 mutant (D541A) mice or Cav1.3 knockout mice. We observed significant nifedipine-sensitive transcellular absorption across the ileum at P14 but not 2 months. Cav1.3 knockout pups exhibited delayed bone mineral accrual, compensatory nifedipine-insensitive Ca2+ absorption in the ileum, and increased expression of renal Ca2+ reabsorption mediators at P14. Moreover, weaning pups at 2 weeks reduced jejunal and ileal Cav1.3 expression. CONCLUSIONS We have detailed novel pathways contributing to transcellular Ca2+ transport across the distal small intestine of mice during development, highlighting the complexity of the multiple mechanisms involved in achieving a positive Ca2+ balance early in life.
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Affiliation(s)
- Megan R. Beggs
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada,The Women’s & Children’s Health Research Institute, Edmonton, Alberta, Canada
| | - Justin J. Lee
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada,The Women’s & Children’s Health Research Institute, Edmonton, Alberta, Canada
| | - Kai Busch
- Experimentelle und Klinische Pharmakologie und Toxikologie, Saarland University, Homburg, Germany
| | - Ahsan Raza
- Experimentelle und Klinische Pharmakologie und Toxikologie, Saarland University, Homburg, Germany
| | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Petra Weissgerber
- Experimentelle und Klinische Pharmakologie und Toxikologie, Saarland University, Homburg, Germany
| | - Jutta Engel
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, School of Medicine, Homburg, Germany
| | - Veit Flockerzi
- Experimentelle und Klinische Pharmakologie und Toxikologie, Saarland University, Homburg, Germany
| | - R. Todd Alexander
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada,The Women’s & Children’s Health Research Institute, Edmonton, Alberta, Canada,Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada,Correspondence Address correspondence to: R. Todd Alexander, MD, PhD, Department of Pediatrics, 4-585 Edmonton Clinic Health Academy, 11405 – 87 Avenue, University of Alberta, Edmonton, Alberta T6G 2R7, Canada. fax: (780) 248-5556.
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Potential Interplay between Hyperosmolarity and Inflammation on Retinal Pigmented Epithelium in Pathogenesis of Diabetic Retinopathy. Int J Mol Sci 2018; 19:ijms19041056. [PMID: 29614818 PMCID: PMC5979527 DOI: 10.3390/ijms19041056] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 03/21/2018] [Accepted: 03/30/2018] [Indexed: 12/15/2022] Open
Abstract
Diabetic retinopathy is a frequent eyesight threatening complication of type 1 and type 2 diabetes. Under physiological conditions, the inner and the outer blood-retinal barriers protect the retina by regulating ion, protein, and water flux into and out of the retina. During diabetic retinopathy, many factors, including inflammation, contribute to the rupture of the inner and/or the outer blood-retinal barrier. This rupture leads the development of macular edema, a foremost cause of sight loss among diabetic patients. Under these conditions, it has been speculated that retinal pigmented epithelial cells, that constitute the outer blood-retinal barrier, may be subjected to hyperosmolar stress resulting from different mechanisms. Herein, we review the possible origins and consequences of hyperosmolar stress on retinal pigmented epithelial cells during diabetic retinopathy, with a special focus on the intimate interplay between inflammation and hyperosmolar stress, as well as the current and forthcoming new pharmacotherapies for the treatment of such condition.
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Willermain F, Libert S, Motulsky E, Salik D, Caspers L, Perret J, Delporte C. Origins and consequences of hyperosmolar stress in retinal pigmented epithelial cells. Front Physiol 2014; 5:199. [PMID: 24910616 PMCID: PMC4038854 DOI: 10.3389/fphys.2014.00199] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 05/09/2014] [Indexed: 01/21/2023] Open
Abstract
The retinal pigmented epithelium (RPE) is composed of retinal pigmented epithelial cells joined by tight junctions and represents the outer blood-retinal barrier (BRB). The inner BRB is made of endothelial cells joined by tight junctions and glial extensions surrounding all the retinal blood vessels. One of the functions of the RPE is to maintain an osmotic transepithelial gradient created by ionic pumps and channels, avoiding paracellular flux. Under such physiological conditions, transcellular water movement follows the osmotic gradient and flows normally from the retina to the choroid through the RPE. Several diseases, such as diabetic retinopathy, are characterized by the BRB breakdown leading to leakage of solutes, proteins, and fluid from the retina and the choroid. The prevailing hypothesis explaining macular edema formation during diabetic retinopathy incriminates the inner BRB breakdown resulting in increased osmotic pressure leading in turn to massive water accumulation that can affect vision. Under these conditions, it has been hypothesized that RPE is likely to be exposed to hyperosmolar stress at its apical side. This review summarizes the origins and consequences of osmotic stress in the RPE. Ongoing and further research advances will clarify the mechanisms, at the molecular level, involved in the response of the RPE to osmotic stress and delineate potential novel therapeutic targets and tools.
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Affiliation(s)
- François Willermain
- Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; I.R.I.B.H.M, Université Libre de Bruxelles Brussels, Belgium
| | - Sarah Libert
- Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium
| | - Elie Motulsky
- Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium
| | - Dany Salik
- Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium ; Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium
| | - Laure Caspers
- Department of Ophthalmology, CHU Saint-Pierre and Brugmann Brussels, Belgium
| | - Jason Perret
- Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Department of Biochemistry, Université Libre de Bruxelles Brussels, Belgium
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Kawano T, Kato M. Electrophysiologic evaluation of retinal pigment epithelial damage induced by photic exposure. Retina 2003; 23:513-7. [PMID: 12972763 DOI: 10.1097/00006982-200308000-00011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To evaluate the retinal pigment epithelial damage induced by light exposure. METHODS One eye of 20 rabbits was exposed to xenon light for 2 hours at an irradiance of 140 mW/cm2 at the surface of the cornea. The contralateral eye served as a control. Forty-eight hours after the light exposure, corneal direct-coupled electroretinograms and the 7% NaHCO3 (bicarbonate) responses of the standing potential were recorded. RESULTS The amplitudes of the a-, b-, and c-waves of the electroretinograms were significantly reduced in the light-exposed eyes, with the c-waves more reduced than the a- and b-waves. The bicarbonate response was also significantly reduced in the irradiated eyes. CONCLUSIONS The decrease of the bicarbonate response of the standing potential indicated that significant functional damage of the retinal pigment epithelium was induced by the light exposure.
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Affiliation(s)
- Toshio Kawano
- Department of Ophthalmology, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu 431-3192, Japan.
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Gupta LY, Marmor MF. Electrophysiology of the retinal pigment epithelium in central serous chorioretinopathy. Doc Ophthalmol 1995; 91:101-7. [PMID: 8813489 DOI: 10.1007/bf01203689] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The pathophysiology of central serous chorioretinopathy is incompletely understood but appears to involve the retinal pigment epithelium. We recorded consecutively the fast oscillation, hyperosmolarity response, acetazolamide response, and light peak from four patients with active central serous chorioretinopathy and three normal subjects to determine whether the affected eyes showed any electrophysical abnormalities. We found essentially no differences in any of the four responses between the active and the inactive eyes of the patients or between patients and normal subjects. Whatever retinal pigment epithelial dysfunction exists in central serous chorioretinopathy is unassociated with clinically evident changes in these retinal pigment epithelial electrophysiologic responses.
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Affiliation(s)
- L Y Gupta
- Department of Ophthalmology, Stanford University Medical Center, USA
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Abstract
There is no ideal electrophysiological test for retinal pigment epithelial (RPE) function. The light-induced responses (EOG, c-wave, fast oscillation) that require photoreception are not pure RPE signals, and even the widely-used EOG has not been associated with any specific physiological disturbance of the RPE or retina. The discovery of non-photic RPE responses (hyperosmolarity, acetazolamide and bicarbonate) has enhanced the possibility of finding tissue-specific RPE tests, but these responses have yet to be correlated with specific RPE functional activity or pathology. We may face a dilemma in our search for RPE tests, insofar as electrophysiology measures membrane changes, but RPE membrane activity is related only indirectly to many functions of the RPE cell. These concerns notwithstanding, RPE electrophysiology can be a valuable clinical tool if one accounts for the physiological limitations and assets of the procedures.
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Affiliation(s)
- M F Marmor
- Department of Ophthalmology, Stanford University School of Medicine, CA 94305
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