CONSERVATION OF STRUCTURE IN ATP-DEPLETED PROXIMAL TUBULES - ROLE OF CALCIUM, POLYPHOSPHOINOSITIDES, AND GLYCINE

Increases of intracellular free Ca2+ (Ca(f)) may mediate phospholipid hydrolysis and disintegration in energy-compromised cells; on the other hand, glycine and related amino acids preserve structure. We have examined the effects of increased Ca(f) on phospholipids and structure in ATP-depleted cells, as well as how these actions may be modified by glycine. Incubation of isolated proximal tubules with antimycin A led to ATP depletion, delayed increases of Ca(f) to micromolar levels, polyphosphoinositide (PPI) hydrolysis by phospholipase C, and generalized disintegration of cell structure. Glycine inhibited PPI hydrolysis and preserved cell structure in entirety but did not apparently modify the Ca(f) increases. When overwhelming increases of Ca(f) were induced by the additional presence of a Ca2+ ionophore, glycine did not inhibit either the hydrolysis of PPI or disruption of mitochondria and microvilli. However, the cells remained integrated and unbroken. Incubation in low-Ca2+ medium prevented Ca(f) increases, inhibited PPI hydrolysis, and preserved the structure of mitochondria and microvilli. Nevertheless, there was lethal damage by disintegration of all other membranes. This damage was prevented specifically and completely by glycine. Thus compartments of cells were shown to be differentially susceptible to injury from increased Ca(f) or lack of glycine. Although damage by either factor occurs by distinct mechanisms, glycine also appears to have effects that suppress the deleterious effects of Ca2+ so long as Ca(f) increases are not overwhelming. Our results also suggest that the PPI have a major structural role, which may be compromised by Ca(f) increase during ATP depletion.