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AIM: To investigate the effect of actin microfilament on potassium current and hyposmotic membrane stretch-induced increase of potassium current in gastric antral circular myocytes of guinea pig.METHODS: Whole-cell patch clamp technique was used to record potassium current in isolated gastric myocyes.RESULTS: When the membrane potential was clamped at-60 mV, an actin microfilament disruptor, cytochanlasin-B(Cyt-B, 20 μmol/L in pipette) increased calcium-activated potassium current (IK(Ca)) and delayed rectifier potassium current (IK(V))to 138.4±14.3% and 142.1±13.1%respectively at +60 mV. In the same condition, an actin microfilament stabilizer phalloidin(20 μmol/L in pipette)inhibited IK(Ca) and IK(V) to 74.2±7.1% and 75.4±9.9%respectively. At the holding potential of -60 mV, hyposmotic membrane stretch increased IK(Ca)and IK(V) by 50.6±9.7%and 24.9±3.3% at +60 mV respectively. In the presence of cytochalasin-B and phalloidin (20 μmol/L, in the pipette)condition, hyposmotic membrane stretch also increased IK(Ca)by 44.5±7.9% and 55.7±9.8% at +60 mV respectively. In the same condition, cytochalasin-B and phalloidin also increased IK(V) by 23.0±5.5% and 30.3±4.5% respectively. However,Cyt-B and phalloidin did not affect the amplitude of hyposmotic membrane stretch-induced increase of IK(Ca)and Ik(V).CONCLUSION: Actin microfilaments regulate the activities of potassium channels, but they are not involved in the process of hyposmotic membrane stretch-induced increase of potassium currents in gastric antral circular myocytes of guinea pig.