Osmosensation in TRPV2 dominant negative expressing skeletal muscle fibres.

Abstract

Increased plasma osmolarity induces intracellular water depletion and cell shrinkage (CS) followed by activation of a regulatory volume increase (RVI). In skeletal muscle, the hyperosmotic shock-induced CS is accompanied by a small membrane depolarization responsible for a release of Ca(2+) from intracellular pools. Hyperosmotic shock also induces phosphorylation of STE20/SPS1-related proline/alanine-rich kinase (SPAK). TRPV2 dominant negative expressing fibres challenged with hyperosmotic shock present a slower membrane depolarization, a diminished Ca(2+) response, a smaller RVI response, a decrease in SPAK phosphorylation and defective muscle function. We suggest that hyperosmotic shock induces TRPV2 activation, which accelerates muscle cell depolarization and allows the subsequent Ca(2+) release from the sarcoplasmic reticulum, activation of the Na(+) -K(+) -Cl(-) cotransporter by SPAK, and the RVI response. Increased plasma osmolarity induces intracellular water depletion and cell shrinkage followed by activation of a regulatory volume increase (RVI). In skeletal muscle, this is accompanied by transverse tubule (TT) dilatation and by a membrane depolarization responsible for a release of Ca(2+) from intracellular pools. We observed that both hyperosmotic shock-induced Ca(2+) transients and RVI were inhibited by Gd(3+) , ruthenium red and GsMTx4 toxin, three inhibitors of mechanosensitive ion channels. The response was also completely absent in muscle fibres overexpressing a non-permeant, dominant negative (DN) mutant of the transient receptor potential, V2 isoform (TRPV2) ion channel, suggesting the involvement of TRPV2 or of a TRP isoform susceptible to heterotetramerization with TRPV2. The release of Ca(2+) induced by hyperosmotic shock was increased by cannabidiol, an activator of TRPV2, and decreased by tranilast, an inhibitor of TRPV2, suggesting a role for the TRPV2 channel itself. Hyperosmotic shock-induced membrane depolarization was impaired in TRPV2-DN fibres, suggesting that TRPV2 activation triggers the release of Ca(2+) from the sarcoplasmic reticulum by depolarizing TTs. RVI requires the sequential activation of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and NKCC1, a Na(+) -K(+) -Cl(-) cotransporter, allowing ion entry and driving osmotic water flow. In fibres overexpressing TRPV2-DN as well as in fibres in which Ca(2+) transients were abolished by the Ca(2+) chelator BAPTA, the level of P-SPAK(Ser373) in response to hyperosmotic shock was reduced, suggesting a modulation of SPAK phosphorylation by intracellular Ca(2+) . We conclude that TRPV2 is involved in osmosensation in skeletal muscle fibres, acting in concert with P-SPAK-activated NKCC1.

• Authors: Nadège Zanou, Ludivine Mondin, Clarisse Fuster, François Seghers, Inès Dufour, Marie de Clippele, Olivier Schakman, Nicolas Tajeddine, Yuko Iwata, Shigeo Wakabayashi, Thomas Voets, Bruno Allard, Philippe Gailly
• Journal: The Journal of physiology (J Physiol) Vol. 593 Issue 17 Pg. 3849-63 (Sep 01 2015) ISSN: 1469-7793 [Electronic] England
• PMID: 26108786 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2015 The Authors. The Journal of Physiology © 2015 The Physiological Society.

Chemical References

• Calcium Channels
• Slc12a2 protein, mouse
• Solute Carrier Family 12, Member 2
• TRPV Cation Channels
• Trpv2 protein, mouse
• Stk39 protein, mouse
• Protein Serine-Threonine Kinases
• Calcium

Topics

• Animals
• Calcium
• Calcium Channels (physiology)
• Cell Size
• Male
• Mice, Inbred C57BL
• Mice, Transgenic
• Muscle Fibers, Skeletal (physiology)
• Osmolar Concentration
• Osmotic Pressure
• Phosphorylation
• Protein Serine-Threonine Kinases (physiology)
• Solute Carrier Family 12, Member 2 (physiology)
• TRPV Cation Channels (physiology)