[CA2-SARCOMA CELLS(](I) AND PH(IN) HOMEOSTASIS IN KAPOSI)

Changes in intracellular pH (pH(in)) and intracellular calcium concent ration [Ca2+](i) play a major role in signal transduction leading to c ell growth, differentiation and transformation. In some tumor cell lin es, vacuolar (V-type) H+-adenosine triphosphatases (ATPases) are impor tant in pi-Ii, regulation. To clarify the neoplastic nature and endoth elial origin of Kaposi sarcoma (KS), pH(in) and [Ca2+](i) and the func tional expression of V-type H+-ATPases were evaluated in cultured endo thelial marker-positive KS cells derived from AIDS-KS skin lesions as compared to human umbilical vein endothelial cells (HUVEC). Human skin fibroblasts (HSF) were also examined. Cells were examined using fluor escence spectroscopy with the pH(in) indicator SNARF-1 and the [Ca2+]( i) indicator Fura-2. We found that whereas pH(in) recovery from acid l oading occurred in the absence of Na+ and HCO3- in HUVEC and HSF, KS c ells did not recover. Moreover, removal of extracellular Na+ had no ef fect on [Ca2+](i) in HUVEC, but transiently increased [Ca2+](i) in KS cells and HSF. This [Ca2+](i) spike was unaffected by Ca2+-free medium , suggesting that it is not due to Na+/Ca2+ exchange. In addition, use of K+-containing and K+-free medium to mimic depolarization or hyperp olarization, which may occur during Na+ removal, did not cause [Ca2+]( i) changes. The [Ca2+](i) levels were also not sensitive to intracellu lar acidification but were specifically sensitive to [Na+]. Thus, RS c ells differ from normal endothelial cells in the kinetics of pH(in) re covery to acid loads, and in the presence of a specific [Na+]-sensitiv e intracellular Ca2+ pool. These differences in ion homeostasis indica te that these cell types are not developmentally related or that alter ations in ion transport are a part of the etiology of the KS lesion.