EFFECTS OF LONG-TERM CHANGES IN MEDULLARY OSMOLALITY ON HEAT-SHOCK PROTEINS HSP25, HSP6O, HSP72 AND HSP73 IN THE RAT-KIDNEY

The influence of diuresis and antidiuresis on the expression of heat s hock proteins (HSP) 25, 60, 72 and 73 in the renal cortex and outer an d 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 stat e by giving normal drinking water again in combination with deamino-D- arginine vasopressin (dDAVP) for 5 days. Western blot analyses reveale d that neither HSP73 nor HSP60 was influenced by any treatment. The HS P72 level in the medulla was markedly reduced (50%) when osmolality wa s lowered and increased when tonicity was high. RNAse protection assay s showed that the effects on HSP72 are parallelled in general by chang es in HSP72 mRNA. While levels of HSP25 were not influenced, isoelectr ic focusing revealed that the degree of phosphorylation of outer and i nner medullary HSP25 increased following both treatments. It thus seem s that HSP73 and HSP60 are not directly involved in the long-term adap tation to varying medullary osmolalities. The correlation between chan ges in osmolality and amounts of the major stress-inducible HSP72 in t he medulla implies that medullary hypertonicity is stressful for kidne y cells. Furthermore, adaptation to pronounced changes in the osmolali ty of the environment most likely involves phosphorylation of HSP25.