Acute phosphate depletion and in vitro rat proximal tubule injury: protection by glycine and acidosis

Abstract

The effects of phosphate (PO4) removal from Krebs Henseleit buffer on freshly isolated rat proximal tubules (rPT) were assessed by measuring Ca2+ uptake (nmol/mg protein), cellular adenosine triphosphate (ATP) (nmol/mg), tissue K+ content (nmol/mg) and lactate dehydrogenase (LDH) as an index of cell integrity. Ca2+ uptake increased by 50% in rPT incubated in zero PO4 medium as compared to control (2.6 +/- 0.1 vs. 3.9 +/- 0.19, P less than 0.001) and LDH release increased 2.5-fold from 14.2 +/- 0.6 to 31.6 +/- 1.6%, P less than 0.001. Neither verapamil (200 microM) nor mepacrine (50 microM) reduced Ca2+ uptake or decreased LDH release suggesting that the increased Ca2+ uptake was not occurring through potential operated channels and that phospholipase-induced cell injury was not the cause of increased LDH release. Either glycine (2 mM) or extracellular fluid acidosis (pH 7.06), however, significantly diminished rPT injury and Ca2+ uptake. Specifically, as compared to the increased LDH released in untreated. PO4-depleted rPT, LDH release was diminished significantly by glycine treatment (31.0 +/- 0.9 vs. 15.5 +/- 1.6%, P less than 0.001) or acidosis (30.3 +/- 0.04 vs. 19.2 +/- 0.9%, P less than 0.01). Ca2+ uptake did not increase in glycine treated tubules (2.6 +/- 0.1 vs. 2.8 +/- 0.2 nmol/mg, NS) or in the presence of acidosis (2.6 +/- 0.1 vs. 2.97 +/- 0.17 nmol/mg, NS). ATP concentrations were markedly reduced by PO4 depletion (2.8 +/- 0.2 vs. 4.8 +/- 0.3 nmol/mg, P less than 0.001) and remained at low levels during either acidosis or glycine-induced protection.(ABSTRACT TRUNCATED AT 250 WORDS)