Effects of porcine diazepam-binding inhibitor on insulin and glucagon secretion in vitro from the rat endocrine pancreas.

Porcine diazepam-binding inhibitor (pDBI) is a novel peptide that has been isolated from the small bowel of the pig, and that occurs also in the islet D-cells. We have studied its effects on hormone release in vitro from the endocrine pancreas of the rat. In isolated islets, pDBI (10(-9)-10(-6)M) did not affect basal insulin release at 3.3 mM glucose, whereas stimulated release at 8.3 mM glucose was dose-dependently suppressed by 32-69% (P less than 0.01). Furthermore, insulin secretion stimulated by either 16.7 mM glucose or 1 mM IBMX (3-isobutyl-1-methylxanthine) or 1 micrograms/ml glibenclamide was suppressed by pDBI at 10(-8) M (by 28-30%, P less than 0.05) and 10(-7) M (by 43-47%, P less than 0.01). In contrast, islet insulin secretion induced by 20 mM arginine was unaffected by these concentrations of pDBI. In the perfused rat pancreas, pDBI (10(-8) M) enhanced by 30% (P less than 0.05) the first phase (0-5 min) of arginine-stimulated insulin release, whereas the second phase (5-20 min) was unchanged. Moreover, pDBI suppressed by 28% (P less than 0.05) the second phase of arginine-induced glucagon release. Arginine-induced somatostatin release was not significantly affected by the peptide. Since pDBI immunoreactivity has been localized also to islet D-cells, the present results suggest that pDBI may act as a local modulator of islet hormone release.     

Proteins of axonal transport: investigation of solubility characteristics and behaviour in gel filtration

Rapid axonal transport of proteins in retinal ganglion cells of the rabbit was studied following intraocular injections of labelled amino acids. Approximately 10% of the transported radioactivity was found in the supernatant following homogenization and high-speed centrifugation of the nerve terminal region. Relatively simple manipulations with ionic strength, pH and the presence of a chelating agent could solubilize an equivalent amount of radioactivity from the pellet. Lithium diiodosalicylate solubilized most rapidly transported membrane proteins. Gel filtration of readily soluble rapidly transported radioactivity gave a main macromolecular radioactive peak with an approximate mol. wt. of 500,000 dalton as determined on Sephadex G-200. However, gel filtration on Sepharose CL-6B gave a mol. wt. of about 160,000 for the same radioactive peak. SDS polyacrylamide gel electrophoresis of rapidly transported soluble proteins and fractions derived from these proteins via gel filtration and ion exchange chromatography revealed in all cases a very complex picture of labelled polypeptides. Thus rapid axonal transport of soluble proteins in this system seems to involve many different macromolecules.     

Nonrandom bioelectrical signals in plant tissue

The results of investigations on nonevoked bioelectrical activity in the India-rubber tree (Ficus elastica) are presented. Metal electrodes inserted into the plant issue were used as the ionic-to-electronic conduction converting elements. Nonevoked pulse bursts were observed with amplitudes in the 10 to 200 microvolts range. An upper limit value of the cell refractory period has been estimated from the maximum pulse frequency observed.     

TRANSPORT OF MICROTUBULAR PROTEIN IN AXONS OF RETINAL GANGLION CELLS

Abstract— Following intraocular injection of [³H]leucine, microtubular protein was isolated by two different methods from the optic pathway of the rabbit. It was found that most of this protein was transported at a slow rate in the axons of retinal ganglion cells. After arrival at the nerve terminals in the lateral geniculate body, the microtubular protein decayed with a half-life of 9 days.     

Patterns of carbon allocation above ground in a deciduous (Vaccinium uliginosum) and an evergreen (Vaccinium vitis-idaea) dwarf shrub

The carbon allocation to current-year shoots of the deciduous Vaccinium uliginosum L. and the evergreen V. vitis-idaea L. was studied in a field experiment using ¹⁴C. During the first week after labelling, 0–50% and 30–80% of the initially assimilated ¹⁴C was lost in V. vitis-idaea and V. uliginosum respectively. Later on, the losses were smaller. After leaf fall in V. uliginosum , 30, 10 and 8% of the initially assimilated ¹⁴C was recovered in the abscised leaves, in plants labelled 1 July, 1 August and 1 September, respectively. The amounts found in the old V. vitis-idaea leaves the year after labelling were 33, 20 and 10%. Only traces of past-year assimilates were found in the current-year V. vitis-idaea leaves, while it was estimated that the V. uliginosum leaves contained 10–15% of the past-year label. It is concluded that V. vitis-idaea is mainly dependent on early summer assimilates - produced by leaves that have overwintered – for the current year shoot growth, while past-years' assimilates probably make an important contribution to the leaf expansion in V. uliginosum. When fruits occurred, a large fraction of the ¹⁴C assimilates was allocated to them.