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This Article Full Text Full Text (PDF) All Versions of this Article: 295/4/F1090    most recent 90365.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Silva, G. B. Articles by Garvin, J. L. PubMed PubMed Citation Articles by Silva, G. B. Articles by Garvin, J. L.

TRPV4 mediates hypotonicity-induced ATP release by the thick ascending limb

¹Division of Hypertension and Vascular Research, Henry Ford Hospital, and ²Department of Physiology, School of Medicine, Wayne State University, Detroit, Michigan

Submitted 12 June 2008 ; accepted in final form 31 July 2008

Extracellular ATP is an autocrine/paracrine factor that regulates renal function. Transient receptor potential vanilloid (TRPV) 4 is a cation channel that mediates release of autocrine/paracrine factors by acting as an osmosensor. The renal medulla, and therefore the thick ascending limb, is exposed to osmotic stress. We hypothesize that reduced osmolality stimulates ATP release from the thick ascending limb via transient receptor potential vanilloid (TRPV) 4 activation. We measured ATP release by medullary thick ascending limb suspensions after reducing bath osmolality from 350 to 323 mosmol/kgH₂O, using the luciferin-luciferase assay. Decreasing osmolality stimulated ATP release compared with control (38.9 ± 7.2 vs. 2.4 ± 1.0 pmol/mg protein; n = 6, P < 0.01). To examine the role of TRPV4, we used 1) Ca-free solutions, 2) a TRPV4 inhibitor, 3) small interfering (si) RNA against TRPV4, and 4) a TRPV4 activator. Removal of Ca completely blocked osmolality-induced ATP release (42.2 ± 5.9 vs. 2.6 ± 1.5 pmol/mg protein; n = 6, P < 0.01). In the presence of the TRPV4-selective inhibitor ruthenium red, osmolality-induced ATP release was blocked by 73% (56.4 ± 19.9 vs. 8.8 ± 2.3 pmol/mg protein; n = 6; P < 0.03). In vivo treatment of thick ascending limbs with siRNA against TRPV4 decreased osmolality-induced ATP release by 62% (31.5 ± 3.4 vs. 12.4 ± 1.1 pmol/mg protein; n = 6; P < 0.01), while reducing TRPV4 expression by 74% compared with the nontreated kidney. Treatment with scrambled siRNA did not affect TRPV4 expression and/or osmolality-induced ATP release. Finally, in the absence of changes in osmolality, the specific TRPV4 agonist 4-PDD increased ATP release (3.6 ± 0.9 vs. 25.4 ± 7.4 pmol/mg protein; n = 6; P < 0.04). We concluded that decreases in osmolality stimulate ATP release by thick ascending limbs and this effect is mediated by TRPV4 activation.

osmosensor; cell swelling, calcium channels, hyposmolality