ABSTRACT
The phospholipase C-catalysed breakdown of inositol-containing phospholipids is an important source of diacylglycerol in cells stimulated by several agonists. However, recent experimental evidence suggests that major phospholipids such as phosphatidylcholine may also be substrates of the phosphodiesteratic hydrolysis activated by hormones, growth factors and oncogene products. We show here that stimulation of muscarinic agonists activates the release of phosphocholine, which, along with diacylglycerol, is a metabolic product of phospholipase C-mediated hydrolysis of phosphatidylcholine. Fluoroaluminates mimic this muscarinic effect, strongly suggesting that carbachol-activated release of phosphocholine may be mediated by a guanine-nucleotide-binding protein. Evidence for this was obtained from experiments using permeabilized cells in which non-hydrolysable analogues of GTP activated phosphocholine release synergistically with carbachol.
Subject(s)
Aluminum Compounds , Atropine/pharmacology , Carbachol/pharmacology , Phosphatidylcholines/metabolism , Receptors, Muscarinic/drug effects , Type C Phospholipases/metabolism , Aluminum/pharmacology , Aluminum Chloride , Animals , Cells, Cultured , Chlorides/pharmacology , Cyclic AMP/analysis , Fibroblasts/drug effects , Fibroblasts/enzymology , Hydrolysis , Mice , Parasympathomimetics/pharmacology , Sodium Fluoride/pharmacologyABSTRACT
The purification to homogeneity of a 60 kDa phosphoinositide-specific phospholipase C from bovine brain cytosol is reported here. This enzyme exhibits the same properties, in terms of response to Ca2+, as does the cytosolic activity in a variety of cell types. We show here that Ca2+ does not appear to modulate the binding of the enzyme to the substrate, but induces dramatic changes in its secondary structure. Therefore we suggest that a decrease in the alpha-helix content of this enzyme correlates with its ability to be activated by Ca2+.
Subject(s)
Brain/enzymology , Calcium/pharmacology , Phosphoric Diester Hydrolases/metabolism , Animals , Cattle , Cell Line , Cytosol/enzymology , Enzyme Activation/drug effects , Phosphatidylinositol Diacylglycerol-Lyase , Phosphoric Diester Hydrolases/isolation & purification , Protein Binding/drug effects , Protein Conformation/drug effectsSubject(s)
Gastric Mucosa/ultrastructure , Stomach Ulcer/metabolism , Animals , Female , Gastric Juice/metabolism , Gastric Mucosa/metabolism , Histamine/metabolism , Histidine Decarboxylase/metabolism , Male , Rats , Stomach Ulcer/enzymology , Stomach Ulcer/pathology , Stress, Physiological/complicationsSubject(s)
Adrenal Glands/metabolism , Hypothalamus/metabolism , Stomach Ulcer/metabolism , 17-Ketosteroids/urine , Animals , Catecholamines/metabolism , Female , Male , Pepsinogen A , Pepsinogens/urine , Rats , Restraint, Physical , Serotonin/metabolism , Stomach Ulcer/etiology , Stress, Physiological/complications , Vanilmandelic Acid/urineABSTRACT
The effects of continuous intravenous perfusion of somatostatin on the incidence of ulcers and the histamine and serotonin gastric mucosal content in rats subjected to 12 h of restraint were studied. 51 sets of Sprague-Dawley male rats (102 animals) were divided at random into two groups. Those in group I were immobilized and treated with an intravenous infusion of isotonic saline solution. Animals in group II were also immobilized and given intravenous cyclic somatostatin dissolved in isotonic saline solution; the initial dose was 25 microgram and a continuous infusion of 2.5 microgram/kg/h was administered thereafter. A decrease in the ulcer index was observed in the rats perfused with somatostatin (p less than 0.01) as well as a decrease in the histamine (p less than 0.001) and serotonin (p less than 0.01) gastric mucosal contents. These effects of somatostatin on restraint-induced stress ulcer in rats are probably to be explained by microcirculatory changes in the gastric mucosa determined by the vasoactive amines (histamine and serotonin). They constitute an important factor in the pathogenesis of these lesions.
