LOSS OF PLASMA-MEMBRANE STRUCTURAL SUPPORT IN ATP-DEPLETED RENAL EPITHELIA

Renal ischemia induces cytoskeletal alterations, membrane perturbation s, including bleb formation, and ultimately membrane lysis. The mechan isms that underlie these alterations are largely unknown. Through the use of isolated rat renal proximal tubule fragments and calibrated mic ropipette techniques, two potential mechanisms for membrane bleb forma tion during ATP depletion were examined: I) decreased cytoskeletal ret ention of the plasma membrane and 2) increased intracellular pressure. Under control conditions, the pressure required to pull the membrane from the underlying cellular matrix was 73 +/- 10 kdyn/cm(2). After 30 min of ATP depletion, this pressure was diminished by >95% and blebs began to emerge from the basal membrane. The intracellular pressure wi thin these blebbed cells was only 0.08 +/- 0.02 kdyn/cm(2). These obse rvations indicate that, during ATP depletion, the strength of membrane retention diminished until the relatively low intracellular pressure was capable of driving membrane bleb formation. Cytochalasin D, which disrupts the actin cytoskeleton, decreased the strength of membrane re tention by 65 +/- 7%. This suggests that, during ATP depletion, altera tions of the actin cytoskeleton may mediate the loss of membrane reten tion.