Downregulation of the renal outer medullary K+ channel ROMK by the AMP-activated protein kinase

作者：Siraskar Ba****heb; Huang Dan Yang; Pakladok Tatsiana; Siraskar Gulab; Sopjani Mentor; Alesutan Ioana; Kucherenko Yulia; Almilaji Ahmad; Devanathan Vasudharani; Shumilina Ekaterina; Foeller Michael; Munoz Carlos; Lang Florian^*

来源：Pflugers Archiv-European Journal of Physiology, 2013, 465(2): 233-245.

DOI：10.1007/s00424-012-1180-1

• Energy depletion
• K+ channels
• ROMK
• Kaliuresis
• Natriuresis

The 5%26apos;-adenosine monophosphate-activated serine/threonine protein kinase (AMPK) is stimulated by energy depletion, increase in cytosolic Ca2+ activity, oxidative stress, and nitric oxide. AMPK participates in the regulation of the epithelial Na+ channel ENaC and the voltage-gated K+ channel KCNE1/KCNQ1. It is partially effective by decreasing PIP2 formation through the PI3K pathway. The present study explored whether AMPK regulates the renal outer medullary K+ channel ROMK. To this end, cRNA encoding ROMK was injected into Xenopus oocytes with and without additional injection of constitutively active AMPK(gamma R70Q) (AMPK(alpha 1)-HA+AMPK(beta 1)-Flag+AMPK gamma 1(R70Q)), or of inactive AMPK(alpha K45R) (AMPK(alpha 1K45R)+AMPK(beta 1)-Flag+AMPK(gamma 1)-HA), and the current determined utilizing two-electrode voltage-clamp and single channel patch clamp. ROMK protein abundance was measured utilizing chemiluminescence in Xenopus oocytes and western blot in whole kidney tissue. Moreover, renal Na+ and K+ excretion were determined in AMPK(alpha 1)-deficient mice (ampk (-/-) ) and wild-type mice (ampk (+/+) ) prior to and following an acute K+ load (111 mM KCl, 30 mM NaHCO3, 4.7 mM NaCl, and 2.25 g/dl BSA) at a rate of 500 mu l/h. As a result, coexpression of AMPK(gamma R70Q) but not of AMPK(alpha K45R) significantly decreased the current in ROMK1-expressing Xenopus oocytes. Injection of phosphatidylinositol PI(4,5)P2 significantly increased the current in ROMK1-expressing Xenopus oocytes, an effect reversed in the presence of AMPK(gamma R70Q). Under control conditions, no significant differences between ampk (-/-) and ampk (+/+) mice were observed in glomerular filtration rate (GFR), urinary flow rate, serum aldosterone, plasma Na+, and K+ concentrations as well as absolute and fractional Na+ and K+ excretion. Following an acute K+ load, GFR, urinary flow rate, serum aldosterone, plasma Na+, and K+ concentration were again similar in both genotypes, but renal absolute and fractional Na+ and K+ excretion were higher in ampk (-/-) than in ampk (+/+) mice. According to micropuncture following a K+ load, delivery of Na+ to the early distal tubule but not delivery of K+ to late proximal and early distal tubules was increased in ampk (-/-) mice. The upregulation of renal ROMK1 protein expression by acute K+ load was more pronounced in ampk (-/-) than in ampk (+/+) mice. In conclusion, AMPK downregulates ROMK, an effect compromising the ability of the kidney to excrete K+ following an acute K+ load.

• 出版日期2013-2