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 othe r hand, glycine and related amino acids preserve structure. We have ex amined the effects of increased Ca(f) on phospholipids and structure i n 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, pol yphosphoinositide (PPI) hydrolysis by phospholipase C, and generalized disintegration of cell structure. Glycine inhibited PPI hydrolysis an d preserved cell structure in entirety but did not apparently modify t he Ca(f) increases. When overwhelming increases of Ca(f) were induced by the additional presence of a Ca2+ ionophore, glycine did not inhibi t either the hydrolysis of PPI or disruption of mitochondria and micro villi. However, the cells remained integrated and unbroken. Incubation in low-Ca2+ medium prevented Ca(f) increases, inhibited PPI hydrolysi s, and preserved the structure of mitochondria and microvilli. Neverth eless, there was lethal damage by disintegration of all other membrane s. This damage was prevented specifically and completely by glycine. T hus 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 h ave effects that suppress the deleterious effects of Ca2+ so long as C a(f) increases are not overwhelming. Our results also suggest that the PPI have a major structural role, which may be compromised by Ca(f) i ncrease during ATP depletion.