Interrelation of phosphoinositide metabolism and ion transport in crab nerve fibres

Modulation of K+ transport across synaptosomes of rat brain by synthetic pyrethroids

Potassium transport across synaptosomes was studied under the influence of two synthetic pyrethroids, (Permethrin, without the cyano group) and Cypermethrin (CPM, with the cyano group). Synaptosomes were isolated from rat brain cerebral cortex and incubated with 40 microM of PM and CPM for 15 min at 37 degrees C. K+ release was monitored by a K(+)-sensitive electrode. CPM caused more K+ release from synaptosomes compared to PM. K+ transport is regulated by Na(+)-K(+)-ATPase, K(+)-ATPase and K+ channels. To understand the mode of action, synaptosomes were preincubated with 9.5 x 10(-3) M ouabain (inhibitor of Na(+)-K(+)-ATPase), 1.7 x 10(-2) M N-ethylmaleamide (K(+)-ATPase inhibitor), and 9.5 x 10(-5) M quinine sulfate (K(+)-channel blocker) for 15 min at 37 degrees C. In the presence of ouabain and N-ethylmaleamide, PM- and CPM-induced K+ release was decreased and in the presence of quinine sulfate, there was no release of K+. Furthermore, the studies indicated that PM and CPM significantly decreased K+ uptake.

Dichlorvos and acetylcholine increase 32P-labelling of phospholipids in cricket central nerve cords

The susceptibility of central nerve cord phospholipids of Acheta domesticus to stress caused by acetylcholine and the organophosphate insecticide dichlorvos was determined in vitro. Both dichlorvos (10(-5) and 10(-4)M) and acetylcholine (5 X 10(-5)M) stimulated increased labelling of nerve cord phospholipids by 32P. Dichlorvos caused a significant release of radiolabelled material to the medium, while acetylcholine did not.

Effect of electrical stimulation on phosphoinositide metabolism in rat sciatic nerve in vivo

The metabolism of phosphoinositides in rat sciatic nerves in vivo during electrical stimulation was studied. Nerves were prelabeled by injection of [2-3H]-myo-inositol alone for periods of 2 and 20 h or together with [32P]orthophosphate for 2 h and then electrically stimulated (100 Hz) for 5 or 20 min. Contralateral unstimulated nerve served as the control. When tritiated myo-inositol was used alone for prelabeling the nerves, approximately 6% and 14% of the label was incorporated into lipids after 2 h and 20 h, respectively. Both 5 and 20 min of electrical stimulation caused an insignificant change in the percentage of radioactivity recovered in lipids from the nerves prelabeled with either myo-inositol or with a mixture of myo-inositol and phosphate. The proportion of label associated with phosphoinositides of nerves prelabeled with myo-inositol for both 2 h and 20 h showed an increase in phosphatidyl-inositol-4-phosphate at the expense of phosphatidylinositol in stimulated nerves. Similar results were obtained with nerves prelabeled for 2 h with a mixture of [32P]orthophosphate and [2-3H]myo-inositol. No significant changes in the radioactivity associated with water-soluble inositol phosphates were found in stimulated versus control nerves.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

ADP-induced changes in [32P]phosphate labeling of phosphatidylinositol-4,5-bisphosphate in washed rabbit platelets made refractory by prior ADP stimulation

Changes in 32P labeling of phosphatidylinositol-4,5-bisphosphate (PIP2) were examined during ADP-induced aggregation of washed rabbit platelets prelabeled with [32P]phosphate. ADP caused a significant decrease in the amount and 32P labeling of PIP2 at 10 and 60 sec. The decrease in labeling persisted at 2.5 min when the platelets were still aggregated, but disappeared by 10 min. Platelets refractory to ADP showed no further significant change in 32P in PIP2 when exposed to ADP; a decrease in PIP2 labeling could be induced, however, after platelets had recovered their disc shape and sensitivity to ADP. These data indicate that PIP2 may play a role in the response of platelets to ADP.

Rapid migration of inositol phospholipids with axonally transported substances in the rabbit optic pathway

Following an intraocular injection of myo-[2-3H]inositol, the axonal transport of labelled water-soluble substances and inositol phospholipids was investigated. Evidence was obtained for a rapid axonal transport of a relatively small amount of labelled inositol phospholipids. In contrast to other axonally transported phospholipids, there was no significant accumulation of labelled, rapidly transported inositol phospholipids in the nerve terminal region at later time intervals following the isotope administration.

Effect of Ca++ on triphosphoinositide extraction in fusing myoblasts

Ca++-dependent degradation of triphosphoinositide has been postulated to regulate levels of membrane-bound Ca++ and to generate a 1,2-diacylglycerol fusogen in cell fusion. Triphosphoinositide metabolism was therefore studied during Ca++-induced fusion of cultured chick embryo myoblasts. Using a frequently cited extraction procedure, it was found that apparent Ca++-dependent triphosphoinositide degradation was actually due to inhibition of extraction. A new procedure using the ion-pairing reagent tetrabutylammonium sulfate was developed which was unaffected by Ca++ and gave 2- to 20-fold greater extraction of triphosphoinositide than existing procedures. With this procedure, no changes in triphosphoinositide metabolism were found during myoblast fusion.

Rapid incorporation in vivo of intracerebrally injected 32Pi into polyphosphoinositides of three subfractions of rat brain myelin

At intervals ranging from 1 to 10 min after injection of 32Pi into rat brain, myelin was prepared and separated into three subfractions: heavy, medium, and light. The radioactivity of total phospholipids and polyphosphoinositides (PPI) was then determined. There was rapid incorporation of 32Pi into PPI, which contained 50-70% of the radioactivity among total brain lipids and more than 70% among myelin lipids. The myelin fraction had incorporated 32Pi into total recovered PPI in the order of medium greater than heavy greater than light fraction; however, the order of relative specific radioactivities was heavy greater than light greater than medium. Labeling of the PPI precursors, phosphatidic acid (PA) and phosphatidylinositol (PI), was considerably lower in the purified myelin than in total brain. The di- (DPI) and triphosphoinositides (TPI) in heavy myelin exchanged 32Pi rates 2 to 3 times faster than those in medium and light myelin. DPI of all subfractions of myelin exchanged much faster than TPI. The results show that the most active phosphate turnover of myelin PPI occurs in the heavy myelin fraction (probably largely consisting of myelin appurtenant regions). However, medium and light myelin (most probably representing the closely packed layers of myelin sheaths) also showed rapid turnover of PPI.

Distribution of phosphoinositides among subfractions of rat brain myelin

Rat brain myelin was separated into three subfractions, heavy, medium, and light, and the concentrations of phosphatidic acids (PA), phosphatidylinositol (PI), di- (DPI), and triphosphoinositide (TPI) in these fractions were determined. PI was evenly distributed among the fractions, and PA, DPI, and TPI occurred in highest concentrations in the "light" myelin. This result indicates that these fast metabolizing lipids play an important role in the tightly packed central lamellae of the myelin sheath.