Effects of long-term changes in medullary osmolality on heat shock proteins HSp25, hsp60, HSP72 and HSP73 in the rat kidney

 The influence of diuresis and antidiuresis on the expression of heat shock proteins (HSP) 25, 60, 72 and 73 in the renal cortex and outer and inner medulla of Wistar rats was analysed. Medullary osmolality was reduced by long-term diuresis (3% sucrose in the drinking water for 3 weeks) and subsequently enhanced by transition to a concentrating state by giving normal drinking water again in combination with deamino-D-arginine vasopressin (dDAVP) for 5 days. Western blot analyses revealed that neither HSP73 nor HSP60 was influenced by any treatment. The HSP72 level in the medulla was markedly reduced (50%) when osmolality was lowered and increased when tonicity was high. RNAse protection assays showed that the effects on HSP72 are parallelled in general by changes in HSP72 mRNA. While levels of HSP25 were not influenced, isoelectric focusing revealed that the degree of phosphorylation of outer and inner medullary HSP25 increased following both treatments. It thus seems that HSP73 and HSP60 are not directly involved in the long-term adaptation to varying medullary osmolalities. The correlation between changes in osmolality and amounts of the major stress-inducible HSP72 in the medulla implies that medullary hypertonicity is stressful for kidney cells. Furthermore, adaptation to pronounced changes in the osmolality of the environment most likely involves phosphorylation of HSP25.