Reduction of Na+ enhances phosphoinositide hydrolysis and differentiates the stimulatory and inhibitory responses to quisqualate in rat brain slices

The concentration of Na+ in the incubation medium significantly influenced phosphoinositide hydrolysis induced by some, but not all, agonists in rat cerebral cortical slices. Reductions of the Na+ concentration below 120 mM resulted in incremental increases in basal and norepinephrine-stimulated accumulation of [3H]inositol monophosphate in cortical slices that had been prelabelled with [3H]inositol, and maximal responses were obtained with 0 and 5 mM Na+. In contrast, the responses to carbachol and ibotenate were similar in medium containing 120 or 5 mM Na+. In medium with 120 mM Na+, quisqualate has two effects on phosphoinositide hydrolysis in cortical slices, including a relatively weak stimulatory effect and an inhibitory modulation of the stimulation induced by norepinephrine. These two responses to quisqualate were differentially modulated by Na+; in 5 mM compared with 120 mM Na+ the stimulatory response was greatly increased and the inhibitory effect was mostly eliminated. That these were two separate events was confirmed by the use of L-BOAA (beta-N-oxalyl-L-alpha, beta-diaminopropionic acid), which reproduces the inhibitory, but not the stimulatory effect of quisqualate on phosphoinositide hydrolysis. In 5 mM Na+, inhibition by L-BOAA of norepinephrine-stimulated phosphoinositide hydrolysis was completely eliminated. These results demonstrate that a physiological concentration of Na+ maintains phosphoinositide hydrolysis at a submaximal level of sensitivity to some, but not all, agonists. The differential effects of Na+ on the stimulatory and inhibitory effects of quisqualate further substantiate the suggestion that these are two separate processes and indicate that alterations of the Na+ concentration may influence the effects of quisqualate, and other agonists, on phosphoinositide hydrolysis.

[Significance of serum procollagen-III-peptide in reflecting the therapeutic effects of calcium-channel blockers on hepatic fibrosis]

Changes in serum procollagen-III-peptide (PIIIP) and intravenous tryptophan tolerance test (ITT) were studied in 121 patients with liver cirrhosis during a follow-up period of up to 18 months. The patients received either nifedipine (31 cases, 60 mg/day), verapamil (28 cases, 120 mg/day), cinnarizine (29 cases, 150 mg/day) or tetrandrine (33 cases, 150 mg/day). The significant changes were found in ITT in any of the four drugs administrated for over three months. Serum PIIIP concentration decreased significantly in patients under tetrandrine therapy for 18 months (12.06 +/- 3.91 ng/ml vs 16.57 +/- 5.69 ng/ml before treatment). These data suggest that tetrandrine therapy may have favourable effects on hepatic fibrosis and improvement of liver function in liver cirrhosis.

Recombination between satellite RNAs of turnip crinkle virus

Turnip crinkle virus (TCV) is associated with satellite (sat) RNAs (sat-RNA D, sat-RNA F), defective interfering (DI) RNAs (DI RNA G, DI1 RNA), and one RNA with properties of both sat-RNAs and DI RNAs (sat-RNA C). When plants were inoculated with TCV, sat-RNA D and in vitro sat-RNA C transcripts containing non-viable mutations in the 5' domain, recombinant sat-RNAs were recovered. These recombinants were composed of sat-RNA D at the 5' end and sat-RNA C sequences at the 3' end. Analysis of 20 independent recombination junctions revealed that unequal crossing-over had occurred in planta in a region of sequence similarity between the two sat-RNAs which resulted in the duplication of 3-16 nucleotides. Thirty percent of the sat-RNA recombinants also had one to three additional nucleotides inserted at the crossover junctions which did not correspond to either sat-RNA C or sat-RNA D sequence. The right side of the recombination junctions always began with one of three consecutive nucleotides of sat-RNA C. Based on the similarity between this sequence of sat-RNA C, the right side junction of DI RNA G and the 5' end of TCV, as well as the sequence similarity between right side junctions of DI1 RNA and sat-RNA C and the 5' end of the sat-RNAs, a replicase-driven copy choice mechanism is proposed.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of phosphoinositide metabolism in rat brain slices by excitatory amino acids, arachidonic acid, and GABA

In rat brain slices the synthesis of [3H]phosphoinositides and the production of [3H]inositol monophosphate (IP1) induced by norepinephrine (NE) were inhibited by glutamate. Calcium concentrations were varied to test if these inhibitory effects of glutamate were mediated by a calcium-dependent process. Although reducing calcium or addition of the calcium antagonist verpamil reduced the inhibitory effects of glutamate, these results were equivocal because reduced calcium directly decreased agonist-induced [3H]phosphoinositide synthesis. The inhibitory effects of glutamate were mimicked by quisqualate in a dose-dependent manner, but none of a variety of excitatory amino acid receptor antagonists modified the inhibition caused by quisqualate. It is suggested that glutamate activates a quisqualate-sensitive receptor (for which an antagonist is not available) and causes inhibition of phosphoinositide hydrolysis mediated in part by a direct or indirect inhibitory effect of calcium on phosphoinositide synthesis. Modulatory effects of arachidonic acid were examined because glutamate and calcium can activate phospholipase A2. Arachidonic acid caused a rapid and dose-dependent inhibition of [3H]phosphoinositide synthesis and of NE-stimulated [3H]IP1 production. A similar inhibition of the response to carbachol also occurred. The inhibition caused by arachidonic acid was unchanged by addition of inhibitors of cyclooxygenase or lipoxygenase. Activation of phospholipase A2 with melittin caused inhibitory effects similar to those of arachidonic acid. Inhibitors of phospholipase A2 were found to impair phosphoinositide metabolism, likely due to their lack of specificity for phospholipase A2. Further studies were carried out in slices that were prelabelled with [3H]inositol in an attempt to separate modulatory effects on [3H]phosphoinositide synthesis and agonist-stimulated [3H]IP1 production. Several excitatory amino acid agonists inhibited NE-stimulated [3H]IP1 production. This inhibitory interaction could be due to impaired synthesis of [3H]phosphoinositides because, even though the slices were prelabeled, addition of unlabelled inositol reduced NE-stimulated [3H]IP1 production, indicating that continuous regeneration of [3H]phosphoinositides is required. In contrast to the inhibitory effects of the excitatory amino acids, gamma-aminobutyric acid (GABA) enhanced the response to NE in cortical and hippocampal slices. GABA also enhanced the response to carbachol in hippocampal and striatal slices and to ibotenic acid in hippocampal slices. Baclofen potentiated the response to NE similarly to the effect of GABA and baclofen partially blocked the inhibitory effect of arachidonic acid but did not alter that of quisqualate.

Turnip crinkle virus defective interfering RNAs intensify viral symptoms and are generated de novo

Defective interfering (DI) RNAs have been isolated from a broad spectrum of animal viruses and have recently been identified in plant virus infections. Because of their ubiquitous nature, DIs are thought to play an important role in virus replication and yields. DI RNAs have now been found in association with a natural isolate of turnip crinkle virus (TCV-B) and are generated de novo after inoculation of turnip with virus derived from cloned transcripts. DI RNA G, naturally found in the TCV-B isolate, is a mosaic molecule with 5' and 3' viral segments and a repeat of 36 nucleotides at the beginning of the 3' segment. The 5'-terminal 21 nucleotides of DI RNA G were not similar to genomic TCV sequences but did resemble sequences found at the 5' end of other small RNAs associated with TCV (satellite RNAs). DI RNA G interferes with the accumulation of TCV genomic RNA and, unlike other DI RNAs, intensifies the symptoms of its helper virus. Infection of turnip with virus derived from cloned transcripts of TCV-B resulted in de novo generation of a DI RNA, DI1 RNA. DI1 RNA differed from DI RNA G by containing exact 5' and 3' ends of TCV as well as an internal virus segment.

Structural characterization of the manganese(IV) Schiff-base complex MnIV(5-Cl-SALAHP)2

Bis[3-(5-chlorosalicylideneamino)propanolato-O,N,O']manganes e(IV) methanol solvate, [Mn(C10H10ClNO2)2].CH3OH, Mr = 510.3, monoclinic, P2(1)/c, a = 11.949 (2), b = 7.530 (2), c = 25.777 (6) A, beta = 105.75 (2) degrees, V = 2232.4 (8) A3, Z = 4, Dx = 1.518 g cm-3, lambda(Mo K alpha) = 0.7107 A, mu = 7.98 cm-1, F(000) = 1502, T = 300 K, R = 0.0343, wR = 0.032 for 2113 unique reflections with (I) greater than 3 sigma(I). The title complex MnIV(5-Cl-SALAHP)2 [5-Cl-SALAHP = 3-(5-chlorosalicylideneamino)propanolato] displays a regular octahedral geometry. The 5-Cl-SALAHP ligand is tridentate, forming a meridional chelate with one phenolato oxygen (Mn-Oavg = 1.90 A), one alkoxide oxygen (Mn-Oavg = 1.85 A) and one imine nitrogen (Mn-Navg = 2.02 A) coordinated to the metal. Important angles described by the six atoms bound to manganese are all very close to either 180 or 90 degrees except the N-Mn-N angle which is 174.7 degrees. Previous studies have shown that MnIV(5-Cl-SALAHP)2 displays a rhombic EPR spectrum with well-resolved 55Mn hyperfine structure on gx, gy and gz. In contrast, Mn(SALADHP)2 [SALADHP = 2-methyl-2-(salicylideneamino)-1,3-propanediolato] shows a broad, ill-defined signal at g = 5.15 and a weak g = 2 component. The different spectral forms result from the extent of distortion of the MnIV octahedron. The reported structure is of potential importance to the understanding of the photosynthetic water-oxidizing system.

[Relationship between blood glucose and serum lipoproteins in alloxan diabetic rabbit]

Blood glucose levels in rabbits were raised and lowered by injections of alloxan and insulin. The relationship between blood glucose and alpha-lipoprotein or beta-lipoprotein were thus examined. The results showed that blood glucose is positively correlated to beta-lipoprotein and negatively correlated to alpha-lipoprotein, and that there exists a definite relation between diabetes mellitus and atherosclerosis. The mechanism remains to be further studied.

Inhibition of receptor-coupled phosphoinositide hydrolysis by sulfur-containing amino acids in rat brain slices

Sulfur-containing amino acids were found to inhibit norepinephrine-stimulated [3H]phosphoinositide hydrolysis in rat cortical slices. Of the amino acids tested, L-cysteine was the most potent, inhibiting the response by 42 and 85% at concentrations of 50 and 500 microM respectively. L-Cystine and L-serine-O-sulfate also inhibited the response to norepinephrine, but to a lesser degree than did L-cysteine. L-Homocysteic acid slightly potentiated phosphoinositide hydrolysis at a concentration of 100 microM, but caused inhibition at 500 microM. L-Cysteine sulfinate produced effects intermediate to those of L-cysteine and L-homocysteic acid, having no effect on the response to norepinephrine at 50 microM, but causing 84% inhibition at 500 microM. The D-isomers of cysteine and homocysteic acid were much less potent than were the L-isomers. Examination of the time course of the inhibition of norepinephrine-stimulated [3H]phosphoinositide hydrolysis by L-cysteine showed that it was inhibited almost completely after 15, 30, 45 and 60 min of incubation. L-Cysteine and L-homocysteic acid caused similarly strong inhibitions of the production of [3H]inositol monophosphate, [3H]inositol bisphosphate and [3H]inositol trisphosphate. The hydrolysis of [3H]phosphoinositides stimulated by norepinephrine in slices from rat hippocampus and striatum were inhibited by L-cysteine to an extent similar to that occurring in cortical slices. These results demonstrate that several sulfur-containing amino acids, some of which have been proposed to be endogenous excitatory amino acid neurotransmitters, effectively modulate the response to norepinephrine of the phosphoinositide second messenger system in rat brain.

Aluminum increases agonist-stimulated cyclic AMP production in rat cerebral cortical slices

The effects of AlCl3 on basal and stimulated cyclic AMP production in rat cerebral cortical slices were studied. AlCl3 (10-250 microM) had no effect on the cyclic AMP concentration in the absence of drugs that stimulate the synthesis of cyclic AMP. 2-Chloroadenosine (25-200 microM) significantly stimulated the synthesis of cyclic AMP in a concentration-dependent manner, and AlCl3 significantly potentiated this response at 50 and 100 microM 2-chloroadenosine. This effect of AlCl3 was dependent on preexposure of the slices to AlCl3 before addition of the agonist. The potentiation by AlCl3 of the 2-chloroadenosine-induced increase in cyclic AMP level was concentration dependent, with significant enhancement by 100 (142% of the control) and 250 (150% of the control) microM AlCl3. Lower concentrations of AlCl3 had no significant effect on the production of cyclic AMP stimulated by 2-chloroadenosine. AlCl3 also potentiated the isoproterenol-induced increase in cyclic AMP production. Forskolin-induced production of cyclic AMP was unaltered by the presence of AlCl3. These results demonstrate that AlCl3 can potentiate agonist-stimulated cyclic AMP production in a whole-cell brain preparation without the addition of fluoride. This may account for the previously reported aluminum-induced increase in cyclic AMP concentrations in rat brain in vivo.

Growth response of B16 melanoma to in vivo treatment with 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) at the initial stage after tumor transplantation

The changes of implanted B16 melanoma fragments in situ following early treatment with 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) were studied by quantitative histopathologic methods from Day 1 to Day 7 and at Day 14 after transplantation. During the first 3-day period there were no apparent differences between the two groups in all the parameters studied. The most striking differences were observed on Day 5 after implantation, when the drug-treated tumor showed the lowest number of morphologically intact tumor cells and the lowest level of proliferative capacity, with a high proportion of melanotic cells. The late infiltration of host macrophages was more abundant in drug-treated tumors than in controls due to an enhanced production and liberation of melanin granules. The results suggest that a 7-day growth delay of drug-treated tumors is characterized not only by a reduced number (one order of magnitude) of intact tumor cells but also by a severely suppressed proliferative capacity.

Plantlet regeneration from mesophyll protoplasts of Digitalis lanata Ehrh

Protoplasts were isolated from the mesophyll of Digitalis lanata enzymatically and cultured in a liquid regeneration medium (D2a). Protoplast division occurred at a rate of approximately 30%. Mature cell colonies were transferred onto agar medium (D2b)where they developed into cell clusters with a diameter of about 4-5 mm. After transfer onto MS medium, these calli differentiated leaves and shoots which could be rooted on MS medium containing a low hormone concentration.