| Research Abstract |
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
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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. Less
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