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(I_(K(Ca)))and delayed rectifier potassium current(I_(K(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 I_(K(Ca))and I_(K(V))to 74.2±7.1% and 75.4±9.9% respectively.At the holding potential of-60 mV,hyposmotic membrane stretch increased I_(K(Ca))and I_(K(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 I_(K(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 I_(K(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 I_(K(Ca))and I_(K(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. 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 (I_ (K (Ca) rectifier potassium current (I_ (K (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 I_ (K (K (V)) to 74.2 ± 7.1% and 75.4 ± 9.9% respectively. The holding potential of -60 mV, hyposmotic membrane stretch increased I_ (K (Ca)) and I_ (K )) 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, hyposmoti Cytochalasin-B and phalloidin also increased I_ (K (V)) by 44.0 ± 7.9% and 55.7 ± 9.8% at + 60 mV respectively. In the same condition, cytochalasin-B and phalloidin also increased I_ 5.5% and 30.3 ± 4.5% respectively. Although Cyt-B and phalloidin did not affect the amplitude of hyposmotic membrane stretch-induced increase of I_ (K (Ca)) and I_ (K (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.