| Being an important componet of plasma membrane, unsaturated fatty acids can not only keep plasma membrane fluidity and stability, but also affect cell functions through modulating some signal transduction. Unsaturated fatty acids include ployunsaturated fatty aicds and monounsaturated fatty acids. Arachidonic acid (AA) and linoleic acid (LA) are to -6 polyunsaturated fatty acids, while oleic acid (OA) is to -9 monounsaturated acid. The modulation of these unsaturated fatty aicds on ion channels is complicated. They can affect ion channels via both the interaction between fatty acids and ion channels protein or the interference with plasma membrane and their cycooxygenase, lipoxygenase, epoxygenase metabolites or cellular signal transduction pathways. In our previous study, we have reported that AA and other unsaturated fatty acids directly inhibited calcium current (ICa), Cl- current (ICl) and muscarinic current (ICCh). However, the effect of unsaturated on calcium-activated potassium current and the mechanism are not clear.In this study, the effect of unsaturated fatty acids on calcium-activated potassium current and its mechanism were investigated in gastric antral circular myocytes of guinea pig. The results are as below:1. Under the whole cell configuration, the membrane potential was clamped at -60 mV. When pipette solution contained egtazic acid 0.1 mmol L-1, IK(Ca) was elicited by step voltage command pulse from -40 mV to +100mV for 440ms with a 20mV increment at 10 sec intervals. An unsaturated fatty acid, arachidonic acid (AA, with 4 double bonds) significantly increased IK(Ca) in a dose-dependant manner. AA increased IK(Ca) by 15.9 3.6%, 31.9 + 7.0%, 46.3 + 10.4% at 2, 5, and 10 mol L-1 at +60 mV, respectively.2. Under the whole patch clamp mode and with the same pipette solution, the holding potential was clamped at -20 mV. The spontaneous transient outward currents (STOCs) was then recorded. 10 mol L-1 AA markedly increased STOCs.3. Another unsaturated fatty acid, linoleic acid (LA, with 2 double bonds) also increased IK(ca) by 27.8 4.8%, 37.9 13.9% , 70.8 + 19.9% at the concentration of 5, 10, and 20 mol L-1 at +60 mV, respectively.4. To determine the inhibitory potency of unsaturated fatty acids, the effects of different unsaturated fatty acids on IK(Ca) were compared. Under the whole-cell configuration, the same concertration (10 mol L"1) of AA, LA, and oleic acid (OA, one double bond) increased /K(ca) by 46.3 10.4%, 37.9+ 13.9% and 13.5 + 5.1% at +60mV, respectively . The increased potency sequence was AA (C20: 4, cis-5, 8, 11, U)>LA (CIS: 2, cis-9, ]2)>OA (C18: 1, cis-9).5. In the presence of H-7 (protein phosphorylation C inhibitor, 10 fimol L"1) 10 Hmol/L AA still increased /K(Ca> by 41.8 3.7 % at +60mV. There was no significant difference between two groups before and after pretreatment with H-7. H-7 also not blocked AA-induced increase of STOCs. In the presence of indomethacin (Indo, the cyclooxygenase inhibitor, 10 nmol L"1) and 17-octadecynoic acid (17-ODA, cytochrome P450 inhibitor, 10 |imol L"1), 10 \imol L"1 AA increased /K(ca) by 42.9 10.8 % and 40.8 6.8 % at +60mV.There was no significant difference between two groups before and after pretreatment with Indo or 17-ODA. However, in the presence of nordihydroguaiaretic acid(NDGA, the lipoxygenase inhibitor, 10 mol L"1), 10 mol L'1 AA increased /K(Ca) by 1 1.3 4.3% at +60mV. There was no significant difference between two groups before and after pretreatment with NDGA.The conclusion: 1) /K(Ca) was increased by unsaturated fatty acid in dose-dependant manner; 2) There was a correlation between the degree of cis unsaturation and the increasing potency of /K(Ca) by unsaturated fatty acids; 3) Unsaturated fatty acid-induced increase of /K(ca) was mediated by lipoxygenase metabolism pathway... |
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