CYTOSOLIC PH REGULATION IN DENSITY-DEFINED SUBPOPULATIONS OF BRONCHOALVEOLAR MACROPHAGES

Bronchoalveolar macrophages (m phi) represent a heterogeneous populati on of morphologically and functionally distinct cells. In mixed popula tions of bronchoalveolar m phi, cytosolic pH (pH(i)) regulation has be en shown to involve both Naf-dependent and -independent mechanisms for H+ extrusion, i.e., passive H+ extrusion in exchange for extracellula r Na+ (Na+-H+ exchange or NHE) and active Hf extrusion by plasmalemmal vacuolar-type H+-ATPase (V-ATPase), respectively. The present studies explored the possibility that individual subpopulations of bronchoalv eolar m phi possess distinct ensembles of H+ extrusion mechanisms. Rab bit bronchoalveolar m phi were separated into five density-defined sub populations using a discontinuous density gradient. Scanning and trans mission electron microscopy revealed morphological differences between the subpopulations. The number of plasmalemmal projections and electr on-dense inclusions increased with increments in cell density. The sub populations were also functionally distinct. Fc receptor-mediated phag ocytosis increased in the increasing density subpopulations. Despite t hese differences, all subpopulations displayed Na+-dependent and -inde pendent mechanisms for pH(i) recovery from intracellular acid loads (a mmonia prepulse technique). We conclude that NHE and V-ATPase activiti es were present in each subpopulation. These findings support the use of mixed populations to study pH(i) homeostasis in bronchoalveolar m p hi.