Gap junctions in the liver of parasitic adult lampreys, Petromyzon marinus L.

Thin-section and freeze-fracture observations of the plasma membranes of hepatocytes from parasitic adult lampreys, Petromyzon marinus, reveal large (250 nm - 4.5 micrometers diameter) gap junctions of highly irregular configuration. The multiformity of these junctions is partially due to the fact that they follow the contours of the undulating cell surface of the irregularly shaped hepatocytes. In addition, junctional membrane is characterized by a slight "rippling" which is not seen on adjacent non-junctional membrane. Although some annular-shaped junctions are associated to non-junctional membrane, others seem completely internalized and they surround portions of the cytoplasm. In P-face replicas the gap junctions are seen to be composed of closely packed particles of 6.0-6.5 nm diameter. E-face replicas of junctional membrane are relatively smooth, a fact which may be related to the small size of the intramembranous particles. Differences in size and shape of gap junctions in hepatocytes of larval (Peck et al. 1979) and adult lampreys may reflect the absence of bile canaliculi and bile ducts in the adult liver and an increased role of these junctions in co-ordination of an endocrine secretory mechanism.