| Role of unsaturated fatty acid in stretch-enhanced muscarinic current in guinea-pig gastric myocytesPlasma membrane is a complex excessive molecule style. Since Nicolson mentioned "Fluid mosaic theory" in 1972 and it was confirmed from many aspect, its basic viewpoint is that membrane protein mounts in the membrane lipid, and they have mutual action. As a ingredient of membrane lipid fatty acids have effect on membrane protein and modulate its construction and function. Unsaturated fatty acids include type n-3 and type n-6, among of them the representative fatty acids are arachidonic acid (AA), linoleic acid (LA) and oleic acid (OA) so on. Many investigation demonstrated that unsaturated fatty acids either active or inhibit ion channels. The effect of fatty acids on ion channel are complicated: fatty acid regulation of ion channels is either direct or indirect. The direct modulation changes the conformation of ion channel protein by the interaction between fatty acid and the protein, or through the interference with cell membranes around channels. The indirect influence of arachidonic acid upon channels results from its metabolites caused by cylccoxygenase and lipooxygenase, protein kinase C (PKC)and intracellular calcium. More recently, mechanical stretch could regulate numerous ion channels function had been confirmationed by many scholar. The mechanical stretch could active numerous intracellular signal pathway, but it is quite difficult to make definite, on earth which signal transduction pathways may couple mechanical stress. The mechanism is more complicated how mechanical stress may be sensed and changed it to biochemistry signal. Mechanical stress may be coupled to intracellular signals via integrins and the cytoskeleton or via sarcolemmal proteins, such as phospholipases, ion channels and ion exchangers, finally, increase intracellular Ca2+ concentration. But stress signal may be directly change the ion channel function via the cytoskeleton without the involvement of signal transduction pathways.In this paper we investigated the effect of AA on muscarinic current and its mechanism, also observed whether exogenous unsaturated fatty acid participated in the hyposmotic membrane stretch induced-increase of muscarinic current (ICCh) in gastric antral circular myocytes of guinea-pig.1. Effect of unsaturated fatty acid on muscarinc current(ICCh)Under the whole-cell configuration, the membrane potential was clamped at -20.0mV, and sodium chloride in external solution and potassium chloride in1.1 the pipette solution were replaced by CsCl to block potassium channel, and ICCh was elicited by 50μmol?L-1 Carbachol. AA, an unsaturated fatty acid (with four double bonds) significantly inhibited ICCh in a dose-dependant manner. AA respectively inhibited ICCh to 46%±8%, 23%±5% and 3.8%±0.9% at concentration of 1, 3 and 5 μmol?L-1.1.2 And under the same condition, another unsaturated fatty acids, linoleic acid(LA) also inhibited ICCh in a dose-dependant manner, LA respectively inhibited to 69.17%±0.45%, 35.2%±0.79% and 7.41%±0.15% at 1, 5 and 10?mol?L-1.1.3 Under the whole-cell configuration, same concentration (5μmol?L-1) of AA, LA and OA (with one double bond) inhibited ICCh to 3.76%±0.64%, 35.2±0.79% and 66.62%±0.61% respectively. Compared both of them mutually, the inhibitory potency sequence was AA (C20: 4, cis-5, 8, 11, 14)>LA (C18: 2, cis-9, 12)>OA (C18: 1, cis-9).To determine whether the inhibitory effects of unsaturated fatty acids on ICCh is direct or indirect, the effect of AA on ICCh was observed after pretreated with indomethacin and H-7 aboout10-15 minutes. In the presence of 100?mol?L-1 H-7(protein phosphorylation C inhibitor) and 10?mol?L-1 indomethacin (cyclooxygenase inhibitor), AA still inhibited ICCh to 5.5%±1.4 0.2% and 3.04%±0.5% respectively. Each of them compared with the effect of AA on ICCh, there were no significant difference in the inhibitory effect of AA on ICCh before pretreatment with H-7 and indomethacin and that o... |
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