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

Abstract

This study compares the effects of heat and osmotic stress on heat stress protein (HSP) production while examining the putative protective action of HSPs on modulation of Na +,K +,Cl − and Na +,P i cotransporters in Madin-Darby canine kidney (MDCK) epithelial cells by severe heat stress (46°C, 15 min). Preconditioning heat stress (43°C, 20 min) followed by 4 h recovery at 37°C led to a 35-fold increase of HSP70 mRNA expression measured by Northern blot analysis. The protein content of HSP70 and HSP27, assessed by Western blots, was augmented by 5- and 2-fold, respectively, after 6 h of recovery. In contrast to preconditioning heat stress, hyperosmotic 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. Neither cell survival, assessed as lactate dehydrogenase (LDH) release, nor the 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 these carriers was abolished by severe heat stress while regulation by P 2-purinoceptors 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 prevent severe heat stress-induced inactivation of protein kinase C- and volume-dependent signaling pathways. These results show that in MDCK cells, preconditioning heat stress-induced HSPs are not involved in the regulation of Na +,K +,Cl − and Na +,P i cotransporters and do not protect them from modulation by severe heat stress.