Title

The effect of heat shock on teleost and mammalian renal proximal tubular transport

Date of Completion

January 1997

Keywords

Biology, Animal Physiology

Degree

Ph.D.

Abstract

Cells and organisms can acquire a state of increased tolerance of damaging conditions by previous exposure to damaging conditions. This state of increased tolerance is often associated with increased synthesis and accumulation of heat shock proteins. This protein synthetic response is a useful marker for examination of additional facets of this response. This dissertation examines effects of heat shock protein-inducing conditions on renal proximal tubular transport in two evolutionarily divergent organisms, fish and mammals. To characterize transport, cultured epithelial monolayers of winter flounder renal proximal tubule and a pig kidney cell line, LLC-PK$\sb1$, grown on contractible collagen substratum, were placed in Ussing chambers for measurements of transepithelial fluxes and currents.^ Studies in flounder focused on transport of DAU, a substrate whose transport is characteristic of cellular multiple drug-resistance (MDR) which is often associated with the resistance of cancer to chemotherapy. Net secretory transport of DAU almost doubled with heat shock protein-inducing heat treatment. Because net transepithelial secretion with characteristics of multi-drug resistance-like transport was observed, these studies indicate that this transport process may be a normally occurring aspect of renal physiology. Using immunohistochemistry and transmission electron microscopy, the presence of a transporter usually associated with a multidrug resistant phenotype, p-glycoprotein (p-gp), was detected at the lumenal membranes.^ Monolayers of LLC-PK$\sb1$ cells were used to characterize the effects of heat stress on inorganic sulfate and Na$\sp+$/glucose cotransport. Heat shock protein (hsp)-inducing heat stress increased Na$\sp+$/glucose cotransport and decreased damage to Na$\sp+$/glucose cotransport by more severe heat treatment. These changes were reflected in the V$\rm \sb{max}$ of glucose-dependent current, indicating that changes in total transport capacity occurred. Similarly, damage to TER following severe heat treatment was ameliorated by previous, milder heat treatment. Enhancement was not observed for reabsorptive sulfate transport, and was independent of effects on the Na$\sp+$ gradient, indicating that the effect was specific for the Na$\sp+$/glucose cotransport. The protective and enhancing effects of MHS on Na$\sp+$/glucose cotransport and TER were not reflected in effects of MHS on cell survival or lumenal membrane surface area as indicated by assays of lactate dehydrogenase and alkaline phosphatase. ^