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      Osmotically Induced Conductance and Capacitance Changes in in vitro Perfused Rectal Gland Tubules of Squalus acanthias

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          The rectal gland of Squalus acanthias is critically involved in the homeostasis of NaCl and water metabolism and hence in overall osmoregulation. In the present study, we have examined the acute responses of rectal gland slices and in vitro perfused rectal gland tubule (RGT) cells to the exposure to dilute and hypertonic peritubule solutions. Five series were performed. (i) With changes in osmolality, Western blots to monitor tyrosine, threonine and serine phosphorylation in rectal gland slices did not reveal clear–cut changes in phosphorylation patterns. All other series were performed in in vitro perfused RGT. (ii) Relative cell volume was estimated by fura–2 fluorescence using the emission at the isosbestic excitation wavelength of 360 nm. Hypotonic solution (–100 mmol/l NaCl) reduced fura–2 fluorescence by 16% and hypertonic solution (+100 mmol/l NaCl) had the opposite effect (+12%). (iii) Transepithelial resistance was increased markedly by hypotonic solution, probably by cell swelling, and the opposite was seen with hypertonic solutions. (iv) Whole–cell patch clamp experiments indicated that hypotonic solution hyperpolarized the cells, and increased membrane conductance and membrane capacitance. The latter two changes correlated significantly with each other. Hypertonic solution had the opposite effect. (v) Measurements of the fura–2 fluorescence ratio (340/380 nm) revealed that hypotonic solution (–NaCl) increased cytosolic Ca<sup>2+</sup> activtiy ([Ca<sup>2+</sup>]<sub>i</sub>). Hypertonic solution had no detectable effect on [Ca<sup>2+</sup>]<sub>i</sub>. These data indicate that RGT cells are swollen by removal of NaCl from the bath solution. This causes an increase in [Ca<sup>2+</sup>]<sub>i</sub> and a predominant increase in K<sup>+</sup> conductance and hyperpolarization. Urea apparently permeates these cells quite well and its addition (+U) or its removal (–U) had only moderate osmotic effects. The removal of urea and replacement by mannitol produced effects similar to those seen with hypertonic NaCl solution.

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          Most cited references 6

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          Cloning and characterization of a putative human serine/threonine protein kinase transcriptionally modified during anisotonic and isotonic alterations of cell volume.

          Hepatic metabolism and gene expression are among other regulatory mechanisms controlled by the cellular hydration state, which changes rapidly in response to anisotonicity, concentrative substrate uptake, oxidative stress, and under the influence of hormones such as insulin and glucagon. Differential screening for cell volume sensitive transcripts in a human hepatoma cell line revealed a gene for a putative serine/threonine kinase, h-sgk, which has 98% sequence identity to a serum- and glucocorticoid regulated kinase, sgk, cloned from a rat mammary tumor cell line. h-sgk transcript levels were strongly altered during anisotonic and isotonic cell volume changes. Within 30 min h-sgk RNA was, independent of de novo protein synthesis, induced upon cell shrinkage and, due to a complete stop in h-sgk transcription, reduced upon cell swelling. Comparable changes of sgk transcript levels were observed in a renal epithelial cell line. h-sgk mRNA was detected in all human tissues tested, with the highest levels in pancreas, liver, and heart. The putative serine/threonine protein kinase h-sgk may provide a functional link between the cellular hydration state and metabolic control.
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            The Diversity of Volume Regulatory Mechanisms

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              Arachidonic acid as a second messenger for hypotonicity-induced calcium transients in rat IMCD cells


                Author and article information

                Kidney Blood Press Res
                Kidney and Blood Pressure Research
                S. Karger AG
                12 November 1998
                : 21
                : 5
                : 317-324
                Physiologische Institute, aAlbert–Ludwigs–Universität, Freiburg, und bEberhard–Karls–Universität, Tübingen, Deutschland
                25888 Kidney Blood Press Res 1998;21:317–324
                © 1998 S. Karger AG, Basel

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                Page count
                Figures: 7, References: 45, Pages: 8
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                Original Paper

                Cardiovascular Medicine, Nephrology

                Exocrine secretion, Volume regulation, Cl– channels, K+ channels


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