Particle arrays in the surface membrane of paramecium: Junctional and possible sensory sites

Abstract

Several special arrays of intramembranous particles observed in freeze-fracture replicas on the P face of the cell membrane of Paramecium caudatum are described for the first time. These arrays include bands of closely spaced particles bordering both the cytopharynx and the cytoproct. These arrays, along with the proximate intermembranous links, bear some resemblance to intercellular septate junctions of invertebrates. Linear rows of particles in the surface membrane of the oral region indicate possible sites of direct microtubular attachment to the cytopharyngeal membrane as well as attachment via a microfilament which is inserted between the ribbon of microtubules and the membrane. Circumferentially aligned rows of particles in the contractile vacuole pore membrane also suggest microtubule-to-membrane attachments. Finally large rectilinearly arrayed particle plates are found in the plasma membrane mostly on the anterior ventral surface of the cell. The location suggests that they may be receptors of chemical stimuli.