[Show abstract][Hide abstract]ABSTRACT: To study effects of arachidonic acid (AA) and its metabolites on the hyposmotic membrane stretch-induced increase in calcium-activated potassium currents (I(KCa)) in gastric myocytes.
Membrane currents were recorded by using a conventional whole cell patch-clamp technique in gastric myocytes isolated with collagenase.
Hyposmotic membrane stretch and AA increased both I(K(Ca))) and spontaneous transient outward currents significantly. Exogenous AA could potentiate the hyposmotic membrane stretch-induced increase in I(K(Ca)). The hyposmotic membrane stretch-induced increase in I(K(Ca)) was significantly suppressed by dimethyleicosadienoic acid (100 micromol/L in pipette solution), an inhibitor of phospholipase A2. Nordihydroguaiaretic acid, a lipoxygenase inhibitor, significantly suppressed AA and hyposmotic membrane stretch-induced increases in I(K(Ca)). External calcium-free or gadolinium chloride, a blocker of stretch-activated channels, blocked the AA-induced increase in I(K(Ca)) significantly, but it was not blocked by nicardipine, an L-type calcium channel blocker. Ryanodine, a calcium-induced calcium release agonist, completely blocked the AA-induced increase in I(K(Ca)); however, heparin, a potent inhibitor of inositol triphosphate receptor, did not block the AA-induced increase in I(K(Ca)).
Hyposmotic membrane stretch may activate phospholipase A2, which hydrolyzes membrane phospholipids to ultimately produce AA; AA as a second messenger mediates Ca(2+) influx, which triggers Ca(2+)-induced Ca(2+) release and elicits activation of I(K(Ca)) in gastric antral circular myocytes of the guinea pig.
Full-text · Article · Nov 2005 · Acta Pharmacologica Sinica
[Show abstract][Hide abstract]ABSTRACT: To investigate the effects of exogenous unsaturated fatty acids on calcium-activated potassium current (I(K(Ca))) in gastric antral circular myocytes of guinea pigs.
Gastric myocytes were isolated by collagenase from the antral circular layer of guinea pig stomach. The whole-cell patch clamp technique was used to record I(K(Ca)) in the isolated single smooth muscle cells with or without different concentrations of arachidonic acid (AA), linoleic acid (LA), and oleic acid (OA).
AA at concentrations of 2,5 and 10 micromol/L markedly increased I(K(ca)) in a dose-dependent manner. LA at concentrations of 5, 10 and 20 micromol/L also enhanced I(K(Ca)) in a dose-dependent manner. The increasing potency of AA, LA, and oleic acid (OA) on I(K(Ca)) at the same concentration (10 micromol/L) was in the order of AA>LA>OA. AA (10 micromol/L)-induced increase of I(K(ca)) was not blocked by H-7 (10 micromol/L), an inhibitor of protein kinase C (PKC), or indomethacin (10 micromol/L), an inhibitor of the cyclooxygenase pathway, and 17-octadecynoic acid (10 micromol/L), an inhibitor of the cytochrome P450 pathway, but weakened by nordihydroguaiaretic acid (10 micromol/L), an inhibitor of the lipoxygenase pathway.
Unsaturated fatty acids markedly increase I(K(ca)), and the enhancing potencies are related to the number of double bonds in the fatty acid chain. The lipoxygenase pathway of unsaturated fatty acid metabolism is involved in the unsaturated fatty acid-induced increase of I(K(ca)) in gastric antral circular myocytes of guinea pigs.
Preview · Article · Mar 2005 · World Journal of Gastroenterology