Evidence for a role of protein kinase C alpha in urine concentration

Abstract

PKC is a family of serine-threonine kinases, which plays an important role in kidney function. It can influence tubular transport, renal hemodynamics, cell growth and differentiation. One of the most abundantly expressed isoenzymes in rat kidney is PKC alpha. In mouse kidney, the classical PKC isoenzyme alpha is expressed in glomeruli, cortical collecting duct (intercalated cells only) and medullary collecting duct. To assess the role of PKC alpha in kidney function, PKC alpha knockout mice (-/-) were studied which had been generated before by Michael Leitges. First, PKC alpha -/- mice and littermate wild type mice (+/+) were housed in metabolic cages for 24-hour urine collection with free access to water and comparable food intake. PKC alpha -/- mice showed a higher urine output (mean±SE: 2.4±0.1 vs 1.6±0.1 ml/day, n=6 mice/group, P<0.001) and reduced urine osmolality (2.41±0.04 vs 3.13± 0.11 osmol/kg, P<0.001) than PKC alpha +/+ mice despite a greater urinary vasopressin to creatinine ratio in PKC alpha +/+ mice. Under the same conditions, neither hematocrit (52.9±1.0 vs 51.4±1.2 %) and plasma osmolality (322±5 vs 329±1 mosmol/kg) nor urinary sodium excretion (197±17 vs 174±19 µmol/day) or albumin excretion were different between PKC alpha +/+ and -/- mice. Dietary NaCl deprivation for 6 days did not reveal significant differences in body weight or urinary sodium excretion between the two groups although polyuria and lower urine osmolality persisted in PKC alpha -/- mice. Second, clearance experiments were performed on inactin/ketamine anesthetized mice. PKC alpha -/- mice showed modestly lower glomerular filtration rate and reduced fractional renal fluid reabsorption, accompanied with a lower kidney weight versus PKC alpha +/+ mice. Third, PKC alpha -/- and +/+ mice were i.p. injected with the vasopressin V2-receptor antagonist SR121463 (1 mg/kg) or orally water-loaded (1 ml/16g body weight). The acute diuresis and the fall in urinary osmolality in response to these two maneuvers were not different between PKC alpha -/- and +/+ mice. In comparison, the lower urinary osmolality observed in PKC alpha -/- mice vs. +/+ mice under basal conditions persisted during water restriction for 36h. At last, immunohistochemical and morphological studies were applied on PKC alpha +/+ and -/- mice. The expression of aquaporin-2 in inner medulla was not different between these two groups. Morphological examination revealed no difference in the thickness ratio of inner medulla to cortex between PKC alpha -/- and +/+ mice. In conclusion, PKC alpha appears not to play a major role in renal sodium transport, but contributes to urinary concentrating ability which is consistent with its expression in the medullary collecting duct.

PKC ist eine Familie der Serin-Threoninkinasen, die eine wichtige Rolle in der Nierenfunktion spielen. Sie kann Gefäßdurchblutung, Nierenhämodynamik, Zellenwachstum und -differenzierung beeinflussen. Eines der am häufigsten vorhandenen Isoenzyme in der Ratteniere ist PKC-Alpha. Die vorliegende Arbeit studiert PKC-Alphaknockoutmäuse (-/-), um die Rolle von PKC-Alpha bei der Nierenfunktion zu bestimmen.