Transport Of Secretory Products Research Articles

Monensin Inhibition of Growth of Ryegrass Seedlings

The effects of monensin on plant growth were evaluated using ryegrass seedlings. Monensin inhibited germination by ca. 8% at 10-5 M (ca. 7 mg/L) and ca. 91% at 10-4 M. At 10-4 M monensin, only the shoot emerged from the few seeds that germinated. Similarly, growth was partially inhibited by monensin at 10-5 M and severely inhibited at 10-4 M. Roots were affected more severely than shoots. Ultrastructural analyses of root cells showed alterations in dictyosomes and in the transport of secretory product into the cell wall. These alterations were more severe at 10-4 M than at 10-5 M monensin. At 10-5 M monensin, only the outer cells of the root were affected, whereas at 10-4 M monensin, even the innermost cells of the root showed effects. In addition, at 10-4 M monensin, but not at 10-5 M, ca. 20% of the root tip cells died with prolonged treatment.

Evidence for rapid and concerted turnover of membrane phospholipids in MOPC 41 myeloma cells and its possible relationship to secretion.

Newly synthesized microsomal membrane phospholipids of actively secreting myeloma cells all appear to decay rapidly, with initial half-lives of less than 1 h. Their rates of decay are similar to each other and to the rates observed earlier for the decay of the protein components of the membrane and also for the intracellular turnover of immunoglobulin light chain, the predominant secretory product of these cells. This evidence, which suggests that many different components of the membrane and, therefore, presumably the membrane itself turn over rapidly, provides support for the hypothesis that unidirectional membrane flow, accompanied by rapid synthesis of the membranes at the origin of flow and their rapid degradation at or near the terminus of flow, is the mechanism of intracellular transport of secretory product by the myeloma cell. An attractive feature of this mechanism is that rapid synthesis and degradation of the membranes could provide the driving force for membrane flow.

EM radioautographic studies on the synthesis and transport of phosphatidylcholine in the parotid acinar cells of isoproterenol-treated rats

The secretory process of the exocrine cells includes: 1) synthesis of secretory materials, 2) intracellular transport and packaging in secretory granules, 3) exocyto- tic discharge responding to secretory stimuli and 4) repair of excess plasma membrane. According to the concept by Palade, synthesis and intracellular transport of secretory products are completed within the surrounding membranes. It is particularly interesting to analyze the dynamic aspects of the membranous container under the brisk stage of secretion granule formation. Since phosphatidylcholine(PC) is well known as one of the ubiquitous constituents of biological membranes, the present study was undertaken to examine the incorporation of [3H]-choline into PC and intracellular movement of labelled PC in the parotid gland of stimulated rats by the administration with isoproterenol (IPR) by means of electron microscopic radioautography,Female Wistar rats(200g body weight) were injected intraperitoneally with isopro- terenol-HCL(8mg/100g body weight). Every 2 hours ranging from 0 to 24 hours both sides of the parotid glands were removed and dissected into pieces of lobules.

Composition of cellular membranes in the pancreas of the guinea pig. IV. Polyacrylamide gel electrophoresis and amino acid composition of membrane proteins.

TWO METHODS OF POLYACRYLAMIDE GEL ELECTROPHORESIS (THE ACID METHOD OF EYTAN AND OHAD AND THE NA DODECYLSULFATE (SDS) DISC METHOD OF MAIZEL) HAVE BEEN USED FOR ANALYZING THE PROTEINS OF GEL FRACTIONS ISOLATED FROM THE GUINEA PIG PANCREATIC EXOCRINE CELLS AND IN PARTICULAR THE PROTEINS BOUND TO THE MEMBRANES INVOLVED IN THE SYNTHESIS, INTRACELLULAR TRANSPORT, AND DISCHARGE OF SECRETORY ENZYMES: rough (RM) and smooth microsome (SM) membranes, zymogen granule (ZG) membranes, and plasma membranes (PM). Since in the two systems the electrophoretic mobility of proteins depends on different factors (size, shape, and net charge of molecules in the acid system; size only in the SDS system) a deeper insight into the protein composition of the fractions could be obtained. The gel patterns of RM, SM, and ZG membranes turned out to be accounted for mainly by segregated secretory enzymes (in rough microsomes also by ribosome proteins) and thus were found to share most of the bands. In contrast, with highly purified membrane fractions different patterns were obtained: RM and SM membrane proteins turn out to contain a large number of different proteins with molecular weights varying between approximately 150,000 and 15,000 daltons. The pattern of ZG membranes was greatly different in the two systems: only two bands were separated by the acid method and as many as 23 by the SDS method. PM gave a rather complex pattern in either system. Both ZG membranes and PM were found to contain a large proportion of low molecular weight proteins. Nothing appears in common between the proteins of SM membranes (primarily of Golgi origin) and those of ZG membranes, while the latter and PM exhibit a certain degree of similarity. By amino acid analysis we found only slight differences: relative to the other fractions: RM membranes were higher in basic amino acids and ZG membranes contained a larger amount of methionine. Taken together with recent data on lipid composition and enzyme activities of the same fractions, these results indicate that the membranes of the pancreatic exocrine cells are chemically and functionally distinct, and hence do not mix randomly with one another during the transport of secretory products.

Composition of cellular membranes in the pancreas of the guinea pig. 3. Enzymatic activities.

A COMPARATIVE STUDY OF THE ENZYMIC ACTIVITIES OF MEMBRANE FRACTIONS DERIVED FROM GUINEA PIG PANCREATIC HOMOGENATES HAS YIELDED THE FOLLOWING RESULTS: Rough microsomal membranes (derived from the rough ER) have the reductase activities of the two microsomal electron transport systems but lack enzyme activities of Golgi-type (TPPase) and plasmalemmal-type (5'-nucleotidase, beta-leucyl naphthylamidase, Mg-ATPase). Smooth microsomal membranes (derived primarily from the Golgi complex), zymogen granule membranes, and plasmalemmal fractions possess overlapping enzyme activities of plasmalemmal type, in different relative concentrations for each fraction. In addition, the smooth microsomal membranes exhibit TPPase and ADPase activity and share with rough microsomes the reductase activities of the two electron transport chains. Taken together with recent data on the lipid composition of the same fractions (2), these results indicate that the membranes of the pancreatic exocrine cell are chemically and functionally distinct, and hence do not mix with one another during the transport of secretory products.

MORPHOLOGIC OBSERVATIONS CONCERNING THE RELEASE AND TRANSPORT OF SECRETORY PRODUCTS IN THE ADENOHYPOPHYSIS.

AbstractThe processes involved in the release of secretory products from the parenchymal cells and the movement of these products into the circulating blood were studied by electron microscopic observations on the adenohypophyses of virgin estrous rabbits. The released secretory products were found in the form of discrete granules, with or without a perigranular membrane, in intercellular spaces, between the plasma membrane and the parenchymal basement membrane, in the perivascular space, in the endothelial cytoplasm, and in the lumen of capillaries. Vesicles containing material which resembled that in the perivascular space were observed in endothelial cells.Interpretation of these observations has led to the proposal of the theory that secretory products of the adenohypophysis may be liberated from parenchymal cells in the following way: by fusion of the perigranular membrane with the plasma membrane (merocrine) or by the detachment of small processes containing secretory granules (“microapocrine”). It is further believed that the discharged products may be transported into circulation in three different manners: by diffusion of dissolved material through the fenestrated endothelium, by active transport of dissolved secretory products by the endothelial cells, or by active transport of intact secretory granules through the endothelial cytoplasm.