Influence of dehydratation on glycerophosphorylcholine and choline distribution along the rat nephron

Glycerophosphorylcholine is one of the four major organic osmolytes in rena l medullary cells, changing their intracellular osmolyte concentration in p arallel with extracellular tonicity during cellular osmoadaptation. In this study, the tubular content of glycerophosphorylcholine was quantified in u ntreated and 48-h-dehydrated male rats. A chemiluminescence ultra-micrometh od was developed to measure choline at the picomolar level in single tubule s microdissected from collagenase-treated kidneys. The glycerophosphorylcho line level was calculated as the difference between total choline after aci d hydrolysis and the free tubular choline content. In accordance with the g lycerophosphorylcholine distribution pattern in different renal zones of un treated rats, low amounts of glycerophosphorylcholine were found in all cor tical and outer medullary structures (< 35 pmol/mm), whereas increasing amo unts were detected towards the papillary tip (163 pmol/mm). As a percentage of total choline, the level of free tubular choline varied from 4.2% in ou ter medullary proximal tubules to 30.3% in the inner medullary collecting d ucts adjacent to the outer medulla (IMCD1). Antidiuresis led to a nearly tw ofold increase in glycerophosphorylcholine content in papillary collecting ducts. The osmolality-dependent regulation of organic osmolytes in single m icrodissected tubules has been demonstrated for the first time. Furthermore , the high tubular glycerophosphorylcholine concentration compared to sorbi tol and myo-inositol emphasizes the predominance of glycerophosphorylcholin e: in the inner medulla and papilla of the rat kidney.