Effect of fasting and feeding on synthesis and intracellular transport of proteins in the frog exocrine pancreas.

J W Slot,J J Geuze,G J Strous

doi:10.1083/jcb.80.3.708

Abstract

Frog exocrine pancreatic tissue was studied in vitro under conditions which maintain the differences between tissues from fasted and fed animals. Sodium dodecyl sulfate (SDS) gel electrophoresis after labeling with [14C]amino acids showed that feeding stimulated the synthesis of secretory proteins to the same relative degree as the overall protein synthesis. The intracellular transport of secretory proteins was studied by electronmicroscopy autoradiography after pulse-labeling with [3H]leucine. It was found that the transport route is similar under both feeding conditions. After their synthesis in the rough endoplasmic reticulum (RER), the proteins move through the peripheral elements and cisternae of the Golgi system into the condensing vacuoles. The velocity of the transport increases considerably after feeding. When frogs are fasted, the release of labeled proteins from the RER takes greater than 90 min, whereas after feeding, this happens within 30 min. Comparable differences were observed for transport through the Golgi system. The apparent differences between the frog and mammalian pancreas in the regulation of synthesis, intracellular transport, and secretion of proteins are discussed.

Highlights

The apparent differences between the frog and mammalian pancreas in the regulation of synthesis, intracellular transport, and secretion of proteins are discussed
We found that protein synthesis mainly concerns secretory proteins, which are transported through the cell much more rapidly in fed frogs than in fasted frogs
Secretory proteins were located in bands3, 5, and the complex 7, which dominate in the secretory granule fraction

Summary

Introduction

The apparent differences between the frog and mammalian pancreas in the regulation of synthesis, intracellular transport, and secretion of proteins are discussed. The effect of feeding on the velocity of intracellular transport of secretory proteins has not yet been studied in pancreatic tissue. The exocrine cell of the frog pancreas seemed suitable for studying the process of intracellular transport in relation to different levels of synthesis and secretion. Volume 80 March1979 708-714 vitro synthesized proteins in exocrine pancreatic cells of fasted and fed frogs as studied by electron microscope autoradiography (EMA). The EMA data of both feeding conditions could be compared with each other In both cases, we found that protein synthesis mainly concerns secretory proteins, which are transported through the cell much more rapidly in fed frogs than in fasted frogs

Methods

Results

Conclusion