Mechanisms for K secretion and K reabsorption in the distal tubule

Research Project

Project/Area Number	08671296
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Single-year Grants
Section	一般
Research Field	Kidney internal medicine
Research Institution	Jichi Medical School
Principal Investigator	MUTO Shigeaki Jichi Medical School, Dept Nephrol, Assistant Professor, 医学部, 講師 (40190855)
Co-Investigator(Kenkyū-buntansha)	EBATA Satoru Jichi Medical School, Dept Nephrol, Instructor, 医学部, 助手 (70265247)
Project Period (FY)	1996 – 1997
Project Status	Completed (Fiscal Year 1997)
Budget Amount *help	¥2,300,000 (Direct Cost: ¥2,300,000) Fiscal Year 1997: ¥1,200,000 (Direct Cost: ¥1,200,000) Fiscal Year 1996: ¥1,100,000 (Direct Cost: ¥1,100,000)
Keywords	sodium conductance / potassium conductance / sodium-potassium pump / acute K^+ elevation / membrane crosstalk / K adaptation / K channel
Research Abstract	Previous studies that an acute elevation of peritubular K^+ enhances K^+ secretion and Na^+ reabsorption in the isolated perfused cortical collecting duct (CCD) from rabbit kidneys. To determine the undelying cellular mechanisms, we used microelectrode techniques to assess the membrane properties of principal collecting duct cells in isolated perfused CCDs of control and desoxycorticosterone acetate (DOCA) -treated rabbits following acute stimulation of the basolateral Na^+, K^+ pump by rapidly increasing the bath solution form 2.5 to 8.5 mM K^+. This induced in both groups of tubules, first, a short-lasting hyperpolarization and second, a sustained phase of depolarization of transepithelial, basolateral, and apical membrane voltages. Whereas the transepithelial conductance (G_T) and fractional apical membrane resistance (fR_A) remained unchanged during the initial phase of hyperpolarization, G_T increased during depolarization and fR_A decreased. Perfusion of the lumen with solutions containing either amiloride or Ba^<2+> attenuated the high K^+-induced apical electrical changes, and basolateral strophanthidin abolished both apical and basolateral electrical responses during elevation of K^+ in the bath. From these results we conclude : 1) Acute elevation of basolateral K^+ activates the basolateral Na^+, K^+ pump, which secondarily elevates the apical Na^+ and K^+ conductances ; 2) DOCA pretreatment increases the basolateral K^+ conductances and augments the response to the rise of K^+ of both basolateral Na^+, K^+ pump activity and apical cation conductances.