|Budget Amount *help
¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1995 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1994 : ¥1,400,000 (Direct Cost : ¥1,400,000)
It has been known that cortical collecting duct plays a most important role to regulate renal potassium metabolism, which is confirmed by in vivo clearance study, in vivo micropuncture study, and in vitro microperfu study. In regulation of potassium transport in CCD,aldosterone and luminal volume flow are the main regulator however, other regulator should be considered. Thus I evaluate the regulatory factors affecting potassium transport CCD,by using in vitro isolated tubular microperfusion.
1) The acidification of bathing medium, by reducing bicarbonate concentration from 25 to 5 mEq/L,markedly reduced potassium secretion in rabbit CCD.The suppression of potassium secretion is induced by several transport pathways, such as Na-K ATPase dependent and independent, K channel dependent and independent, Bicarbonate independent, and independent of sodium reabsorption.
2) In the experiment, stated above, I observed that potassium secretion increased by the elimination of bicarbon from bathing m
edium. To evaluate the mechanism of this phenomenon, intracellular pH was measured by fluorescence technique. Intracellular pH in CCD was 7.2 n the basal condition, and it increases markedly by the elimination of bicarbonate to 7.6. These findings suggest that intracellular pH is the important regulator of potassium secretion in rabbit CCD.
3) Morphologically, connecting duct cells preexist to CCD,and in CNT a bulk of potassium is secrelted. In vi condition, luminal potassium concentration goes up from 5.0 mEq/L to 10 to 15mEq/L,at a perfusion rate of 10 nl/min, indicating that in vivo condition, luminal potassium concentration might be higher than the condition, w usually in vitro experimentally used. To evaluate the effect of luminal potassium concentration changes on potassium secretion, the changes of potassium secretion rate was examined in vitro microperfusion, using differen perfusate containing 5.0 to 15.0 mEq/L potassium concentration. The increase of potassium concentration in perfusate induced hyperpolarization of transepithelial voltage and decrease of potassium secretion. These findings indicate that the function of CNT to secrete potassium is another regulator of potassium secretion in CCD.
3)in vivoでは、CCD直前に接合尿細管(CNT)があり、この部分でのK分泌量はCCDと比べかなり多く、管腔内K濃度でみるならば、管腔内灌流液流速を10nl/minにした状態でも、灌流液K濃度は0.5mEq/Lから尿細管0.5mmでも8-10mEq/Lにも上昇する。CNTの長さは皮質部と随質部で異なるものの、0.5-1.0mmはあり、このことから考えると、CCDにいたる管腔内液は10-15mEq/L前後になると考えられる。血管側K濃度を変化させてのK分泌の変化について検討したところ、CCDでの管腔内電位(VT)は過分極し、K輸送量(JK)も変化することが明かとなった。 Less