Ultracytochemical Characteristics of Two Cell Types in the Rat Knee Synovial Membrane.

Abstract

The synovial lining layer consists of two cell types ultrastructurally. It is said that the function of type A cell is phagocytosis and one of type B cell is secretion of synovial fluid, but the details are still obscure. For a better understanding of these mechanisms, the localizations of five phosphatase activities, i.e. Mg2+-activated adenosine triphosphatase (Mg2+-ATPase), Ca2+ -activated adenosine triphosphatase (Ca2+ -ATPase), ouabain-sensitive, potassium-dependent adenosine triphosphatase (Na+, K+ -ATPase), acid phosphatase (ACPase) and thiamine pyrophosphatase (TPPase) activities, were studied ultracytochemically on the rat knee joints. Type A cell had Mg2+ -ATPase and Ca2+ -ATPase activities on the plasma membrane, especially on the filopodia. Type B cell had these activities at the pinocytotic vesicles. Na+, K+ -ATPase, ACPase, TPPase activities were found at the Golgi apparatus of type B cell. ATPase on the plasma membrane is the enzyme which supplies the energy needed at active transport or cytosis. So the localizations of these enzyme activities may raise the possibility that both type A and B cells might have mechanisms governing the intraarticular homeostasis of the synovial fluid. And on type B cell, basic data were given about the function of the Golgi apparatus. Furthermore in the synovial lining layer, type A and B cells will be distinguishable not only structurally but also cytochemically.