Nitroglycerin-induced desensitization of vascular smooth muscle may be mediated through cyclic GMP-disinhibition of phosphatidylinositol hydrolysis

The purpose of this study was to investigate the hypothesis that nitroglycerin-induced desensitization of vascular smooth muscle is mediated through cyclic GMP-disinhibition of phosphatidylinositol hydrolysis. Norepinephrine-induced contraction and increased levels of inositol monophosphate, a measure of phosphatidylinositol hydrolysis, in rat aorta. Prior treatment with nitroglycerin inhibited both the norepinephrine-induced contraction and the elevated levels of inositol monophosphate to the same relative magnitude. The nitroglycerin-induced inhibition of contraction and inositol monophosphate formation were prevented in tissues desensitized with nitroglycerin. These results suggest that: nitroglycerin may inhibit vascular smooth muscle contraction through cyclic GMP-inhibition of phosphatidylinositol hydrolysis and desensitization to the relaxant effects of nitroglycerin may be due to disinhibition of the hydrolysis.     

Vitamins and other metabolites in various sera commonly used for cell culturing

Many cell culture media use different sera to enhance growth. We assayed vitamins and some related metabolites in different sera and identified the concentration of: thiamin, biotin, folates, riboflavin, pantothenates, nicotinates, vitamins B6, B12, A, E, C, and carotenes and some related metabolites: biopterins, free inositol, free and total choline, total carnitines in chicken, horse, rabbit, goat, pig, calf, newborn calf, fetal calf and human sera. Results indicate that vitamin and metabolite content of different sera vary. Such variations could produce fluctuant effects on cell culturings if the metabolite content of the serum is not documented.     

Serotonin-stimulated protein phosphorylation in aortic smooth muscle cells

The effects of serotonin on the formation of inositol phosphates and protein phosphorylation were examined in cultured smooth muscle cells. Serotonin stimulated the formation of [3H]inositol monophosphate, [3H]inositol bisphosphate and [3H]inositol trisphosphate. This effect was prevented by 5-HT2 specific antagonist, 6-methyl-1-(1-methylethyl)ergoline-8-carboxylic acid, 2-hydroxy-1-methylpropyl ester [Z]-2-butenedioate (LY53857). Serotonin stimulated the phosphorylation of many polypeptides, among which a 20 kDa polypeptide was the most prominent. The phosphorylation was also inhibited by LY53857. LY53857 alone produced no effects on protein phosphorylation. The 20 kDa polypeptides were also phosphorylated by the addition of 12-O-tetradecanoylphorbol-13-acetate. These results suggest that serotonin stimulates protein phosphorylation through 5-HT2 receptors and possibly activates protein kinase C in intact vascular smooth muscle cells.     

On the phospholipids of adultAncylostoma caninum

Summary The phospholipid composition ofAncylostoma caninum has been examined. Phospholipids amounted to 0.9% of the wet weight of the parasite. Ethanolamine and choline containing lipids comprised about 76% of the total phospholipids. Lysolecithin, sphingomyelin, phosphatidyl inositol and phosphatidyl serine were present in minor amounts. Cerebrosides and sulfatides were also identified.Acknowledgements. We wish to acknowledge the contributions of Mr Ashok Chopra in the initial part of this work. Thanks are due to Mr Adarsh Kumar for skilled assistance.     

Nitroglycerin-induced desensitization of vascular smooth muscle may be mediated through cyclic GMP-disinhibition of phosphatidylinositol hydrolysis

Summary The purpose of this study was to investigate the hypothesis that nitroglycerin-induced desensitization of vascular smooth muscle is mediated through cyclic GMP-disinhibition of phosphatidylinositol hydrolysis. Norepinephrine-induced contraction and increased levels of inositol monophosphate, a measure of phosphatidylinositol hydrolysis, in rat aorta. Prior treatment with nitroglycerin inhibited both the norepinephrine-induced contraction and the elevated levels of inositol monophosphate to the same relative magnitude. The nitroglycerin-induced inhibition of contraction and inositol monophosphate formation were prevented in tissues desensitized with nitroglycerin. These results suggest that: 1) nitroglycerin may inhibit vascular smooth muscle contraction through cyclic GMP-inhibition of phosphatidylinositol hydrolysis and 2) desensitization to the relaxant effects of nitroglycerin may be due to disinhibition of the hydrolysis.Acknowledgments. This work was supported by grants from the Veterans Administration, American Heart Association Southwestern Ohio Chapter, and BRSG 507 RR05-408-24 and RO1 HL 34895 from the National Institutes of Health to RMR. JKC is a recipient of a Key Pharmaceutical Company Predoctoral Fellowship. Address all correspondence to R. M. Rapoport.     

Phenytoin-induced DNA synthesis and inositol 1,4,5-trisphosphate formation in L-929 fibroblasts

Culture of L-929 fibroblasts in the presence of phenytoin (2.5-5.0 micrograms/ml) increased DNA synthesis, as indicated by increased [3H]thymidine uptake, while a higher dose (20 micrograms/ml) inhibited DNA synthesis. In like manner, a low dose of phenytoin (5.0 micrograms/ml) was effective in increasing inositol 1,4,5-trisphosphate formation while a higher dose (10 micrograms/ml) tended to inhibit this activity. These data suggest that the formation of inositol phosphate second messengers may play a role in phenytoin-induced fibroblast proliferation and connective tissue growth.     

Serotonin-stimulated protein phosphorylation in aortic smooth muscle cells

Summary The effects of serotonin on the formation of inositol phosphates and protein phosphorylation were examined in cultured smooth muscle cells. Serotonin stimulated the formation of [³H]inositol monophosphate, [³H]inositol bisphosphate and [³H]inositol trisphosphate. This effect was prevented by 5-HT₂ specific antagonist, 6-methyl-1-(1-methylethyl)ergoline-8-carboxylic acid, 2-hydroxy-1-methylpropyl ester [Z]-2-butenedioate (LY53857). Serotonin stimulated the phosphorylation of many polypeptides, among which a 20 kDa polypeptide was the most prominent. The phosphorylation was also inhibited by LY53857. LY53857 alone produced no effects on protein phosphorylation. The 20 kDa polypeptides were also phosphorylated by the addition of 12-O-tetradecanoylphorbol-13-acetate. These results suggest that serotonin stimulates protein phosphorylation through 5-HT₂ receptors and possibly activates protein kinase C in intact vascular smooth muscle cells.Part of the data contained in this paper was presented at the 74th local meeting of the Japanese Society of Pharmacology at Kanagawa.     

Phospholipid metabolism in pancreatic islets

Conclusions The secretion of insulin can be elicited by a wide spectrum of stimuli including nutrients, hormones and neurotransmitters as well as a large number of pharmacological agents such as tumor-promoters and sulphonylureas. The diversity of these secretagogues suggests that islets may be activated through a number of distinct biochemical mechanisms. The work discussed in this review suggests that certain of the above-mentioned secretagogues, especially nutrient and neurotransmitter stimuli, may induce insulin secretion by a mechanism involving enhanced metabolism of inositol-containing lipids. The way in which this process is coupled to secretion is not known, although several possibilities exist. The hydrolysis of phosphoinositides and release of inositol phosphates may result, respectively in altered calcium permeability of the plasma membrane and mobilization of calcium from intracellular sources. The accompanying production of diacylglycerol might also influence membrane permeability and fluidity and also lead to activation of protein kinase C. Diacylglycerol can be phosphorylated to form phosphatidic acid which may play a role as an endogenous ionophore. Finally, inositol lipid breakdown could lead, through diacylglycerol and/or phosphatidic intermediates, to the liberation of arachidonic acid and subsequent conversion to active metabolites of the cyclo-oxygenase and lipoxygenase pathways. Thus, enhanced phospholipid metabolism in islets could, theoretically, result in the generation of a range of intracellular signals which mediate or modulate insulin secretion during stimulation by certain types of secretagogues. Continued investigation is clearly neccessary in order to elucidate the mechanisms by which such secretagogues provoke increased phospholipid metabolism and to understand the role(s) of this process in the regulation of islet function.     

Suspension culture ofNigella sativa

Summary In suspension culture 91% free cells ofNigella sativa was obtained inWhite's medium supplemented with casein hydrolysate, inositol and adenine. Ploidy distribution pattern was similar in cell clumps of different sizes and free cells. Chromosomal irregularities were more in free cells. A number of globular embryoid were formed when casein hydrolysate, inositol and adenine were added in the medium after subsequent omission of auxin and coconut milk.