Synthesis and intracellular transport of proteins in the exocrine pancreas of the frog (Rana esculenta). II. An in vitro study of the transport process and the influence of temperature.

Frog pancreatic tissue was pulse-labelled in vitro with 3H-leucine and protein transport was studied in exocrine cells by electron microscope autoradiography. The proteins appeared to be synthesized in the RER and transported to the secretory granules along a similar route and with the same velocity as previously described under in vitro conditions. Evidence was obtained for the involvement of the vesicular and tubular elements at the periphery of the Golgi system in transferring protein from the RER to the Golgi cisternae. Kinetics of the release of newly synthesized proteins from the RER and their appearance in the condensing vacuoles are discussed and related to results reported from other tissues. The transport velocity in this poikilothermic system was studied in relation to the incubation temperature and compared with results reported from its mammalian counterpart. At temperatures between 20 and 30 degrees C intracellular protein transport occurs faster in the frog than in the Guinea pig pancreas. At higher temperature the transport process was severely disturbed in the frog.