DEGRADATION OF SPECTRIN AND ANKYRIN IN THE ISCHEMIC RAT-KIDNEY

This study investigates ischemia-induced degradation of the spectrin-b ased cytoskeleton in rat brain, heart, and kidney. Spectrin, in conjun ction with ankyrin, structurally supports the plasma membrane and sequ esters integral membrane proteins. After 60 and 120 min of ischemia, b rain tissue displayed both spectrin and ankyrin breakdown. The spectri n fragmentation pattern is similar to previously reported ischemia-ind uced calpain I proteolysis of spectrin in N-methyl-D-aspartate recepto r-containing neurons. Ischemic heart tissue displayed no spectrin or a nkyrin degradation. Ischemic renal tissue showed minimal breakdown of spectrin but a major loss of ankyrin (25%/30 min of ischemia) that was essentially complete after 120 min of ischemia. Interestingly, this p rofound loss of ankyrin in the intact ischemic kidney was not mimicked in three renal cell lines (MDCK, LLC-PK1, and JTC cell lines) exposed to chemical anoxia. Immunocytochemistry showed ankyrin was concentrat ed in thick ascending limb (cTAL) cells and, although delayed by 30 mi n, was lost at the same rate as measured by immunoblot analysis. Spect rin and Na+-K+-ATPase, which complex with ankyrin, were essentially un affected by ischemia. Ankyrin degradation in cTAL cells correlated wit h the loss of basal infolding organization. In conclusion, the spectri n - based cytoskeleton is differentially targeted by ischemia-induced degradative processes in different in vivo tissues.