Heat stress ameliorates ATP depletion-induced sublethal injury in mouse proximal tubule cells

The role of prior heat stress (HS) in ameliorating changes in the actin cytoskeleton and the loss of tight junction integrity that accompany ATP depletion was examined. Mouse proximal tubule cells in primary culture were exposed to sodium cyanide (CN) in the absence of dextrose for 1 h, a maneuver that produced equivalent degrees of ATP depletion in control and in HS cells. After ATP depletion, actin stress fibers were completely disrupted in control cells. In contrast, HS cells with elevated HSP-72 content showed preservation of stress fibers after CN exposure. ATP depletion in control and HS cells produced similar and reversible depletion of the G-actin pool without altering total actin content. Integrity of the tight junction was assessed by transepithelial electrical resistance (TER) and unidirectional flux of lucifer yellow (LY, mol wt 482). After CN alone, the nadir in TER was lower than that of HS + CN cells (51.6 +/- 2.5 vs. 96.2 +/- 3.2 Ohm . cm(2), respectively; P < 0.05). After 30-min recovery, TER of HS + CN recovered to control values (277 +/- 7.2 vs. 227 +/- 6.6 Ohm . cm(2); P > 0.05), whereas CN did not (165 +/- 7.3 vs. 227 +/- 6.6 Ohm . cm(2); P < 0.05). Changes in LY flux paralleled those in TER. HS is associated with preservation of the actin cytoskeleton and improved integrity of the tight junction after sublethal ATP depletion injury. These protective effects may contribute to the preservation of epithelial cell polarity and function following an ischemic insult.