title: STE20/SPS1-related proline/alanine-rich kinase (SPAK) is critical for sodium reabsorption in isolated, perfused thick ascending limb.
abstract: SPAK [STE20 (sterile 20)/SPS1-related proline/alanine-rich kinase] kinase consists of a full-length (FL-) and an alternatively spliced kidney-specific (KS-) isoform. SPAK regulates the NaCl cotransporter (NCC) in the distal convoluted tubule (DCT). The relative abundance and role of FL- vs. KS-SPAK in regulating Na(+)-K(+)-2Cl(-) cotransporter (NKCC2) in thick ascending limb (TAL) are not completely understood. Here, we report that FL-SPAK mRNA was the most abundant in medullary TAL (mTAL), followed by cortical TAL (cTAL) and DCT. KS-SPAK mRNA abundance was relatively lower than FL-SPAK. The ratios of FL-SPAK to KS-SPAK in mTAL, cTAL, and DCT were 12.3, 12.5, and 10.2, respectively. To examine the role of SPAK in the regulation of sodium transport in TAL, we used in vitro microperfusion of mTAL and cTAL isolated from wild-type (WT) and SPAK knockout mice (SPAK-KO) that lack both FL- and KS-SPAK. The rates of sodium absorption in cTAL and mTAL of SPAK-KO mice were 34.5 and 12.5% of WT tubules, respectively. The mRNA levels of related OSR1 kinase and SPAK protease Dnpep in SPAK-KO tubules were not significantly different from WT tubules. We next examined the role of SPAK in the regulation of sodium reabsorption by vasopressin in TAL. Vasopressin increased sodium reabsorption by ∼80% in both mTAL and cTAL from WT mice. While baseline sodium reabsorption was lower in SPAK-KO tubules, vasopressin increased sodium reabsorption over twofold. In conclusion, the combined net effect of SPAK isoforms on sodium reabsorption in TAL is stimulatory. SPAK is not essential for vasopressin stimulation of sodium reabsorption in TAL.
authors.affiliation: Department of Medicine, Division of Nephrology, UT Southwestern Medical Center, Dallas, Texas; Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, Taipei 114, Taiwan laurence1234kimo@yahoo.com.tw.
authors.forename: Chih-Jen
authors.initials: CJ
authors.lastname: Cheng
authors.affiliation: Department of Medicine, Division of Nephrology, UT Southwestern Medical Center, Dallas, Texas;
authors.forename: Joonho
authors.initials: J
authors.lastname: Yoon
authors.affiliation: Department of Medicine, Division of Nephrology, UT Southwestern Medical Center, Dallas, Texas; Department of Pediatrics, UT Southwestern Medical Center, Dallas, Texas; and.
authors.forename: Michel
authors.initials: M
authors.lastname: Baum
authors.affiliation: Department of Medicine, Division of Nephrology, UT Southwestern Medical Center, Dallas, Texas;
authors.forename: Chou-Long
authors.initials: CL
authors.lastname: Huang
mesh_terms: D000818:Animals; D043384:Glutamyl Aminopeptidase / Q000378:metabolism; D066298:In Vitro Techniques; D008138:Loop of Henle / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020033:Protein Isoforms / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D065608:Renal Reabsorption; D012964:Sodium / Q000378:metabolism*; D064466:Solute Carrier Family 12, Member 1 / Q000378:metabolism; D014667:Vasopressins
chemical_list: D020033:Protein Isoforms; C578715:Slc12a1 protein, mouse; D064466:Solute Carrier Family 12, Member 1; D014667:Vasopressins; D012964:Sodium; C486407:Stk39 protein, mouse; C534421:OXSR1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D043384:Glutamyl Aminopeptidase
keywords: SPAK; sodium; thick ascending limb; vasopressin