ATPase activities are restricted to the apical and lateral domain of the plasma membrane in parathyroid cells

Abstract

The cytoplasmic calcium concentration is about 10-7 mol, that of the extracellular space 10-3 mol. There is evidence that Ca++-ATPase is directly and indirectly involved in the maintenance of this gradient. Ca++-ATPase was found in isolated parathyroid (PT) cell membranes considering that a substantial proportion was bound to the plasma membrane (Bess et al. 1983). We, therefore, intended to localize Ca++-ATPase activity in situ. Cytochemical demonstration revealed Ca++-ATPase to be present at the apical and lateral domain of the plasma membrane in bovine PT cells.Bovine PT glands were harvested immediately after slaughter, washed in ice cooled PBS, disected and immersed in 2% formaldehyde and 1% glutaraldehyde in 0.1M Na-cacodylate, pH 7.4, for 1 hour at 4°C. After washing or storage (maximal 24 hours), 50 μm sections were cut on a vibratome, incubated for demonstration Ca++-, Mg++-, and Na+- K+- dependent ATPase activity, post fixed with 1% OsO4 and processed for electron microscopy.