Heat stress preconditioning does not protect renal epithelial Na+,K+,Cl- and Na+,P-i cotransporters from their modulation by severe heat stress

This study compares the effects of heat and osmotic stress on heat stress p rotein (HSP) production while examining the putative protective action of H SPs on modulation of Na+,K+,Cl- and Na+,P-i cotransporters in Madin-Darby c anine kidney (MDCK) epithelial cells by severe heat stress (46 degrees C , 15 min). Preconditioning heat stress (43 degrees C, 20 min) followed by 4 h recovery at 37 degrees C led to a 35-fold increase of HSP70 mRNA expressio n measured by Northern blot analysis. The protein content of HSP70 and HSP2 7, assessed by Western blots, was augmented by 5- and 2-fold, respectively, after 6 h of recovery. In contrast to preconditioning heat stress, hyperos motic stress (520 vs. 320 mosm) elevated HSP70 mRNA content only by 7-fold and did not significantly affect the protein content of HSP70 or HSP27. Nei ther cell survival, assessed as lactate dehydrogenase (LDH) release, nor th e basal activities of the ion transporters and their modulation by protein kinase C, P-2-purinoceptor and cell volume were altered by preconditioning heat stress. Severe heat stress increased extracellular LDH content from 3 +/- 2 to 23 +/- 5% and enhanced Na+,K+,Cl- and Na+,P-i cotransport activity by 2-3-fold. The volume- and protein kinase C-dependent regulation of thes e carriers was abolished by severe heat stress while regulation by P-2-puri noceptors was preserved. Preconditioning heat stress diminished severe heat stress-induced LDH release to 11 +/- 4% but did not protect Na+,K+,Cl- and Na+,P-i cotransporters from activation by severe heat stress and did not p revent severe heat stress-induced inactivation of protein kinase C- and vol ume-dependent signaling pathways. These results show that in MDCK cells, pr econditioning heat stress-induced HSPs are not involved in the regulation o f Na+,K+,Cl- and Na+,P-i cotransporters and do not protect them from modula tion by severe heat stress. (C) 1999 Elsevier Science B.V. All rights reser ved.