ABSTRACT
AIM: To investigate the effect of Ginkgolide B (GB) on action potential (AP), delayed rectifier potassium current (IK), and L-type calcium current (I(Ca-L)) in guinea pig ventricular myocytes. METHODS: Single ventricular myocytes were isolated by an enzymatic dissociation method. AP, IK, I(Ca-L) were recorded by whole-cell patch-clamp technique in either current or voltage clamp mode. RESULTS: GB shortened APD in a concentration-dependent manner. GB 0.1, 1, and 10 micromol/L shortened APD50 by 7.9% (n=5, P>0.05), 18.4% (n=5, P<0.01), and 28.9% (n=6, P<0.01), respectively; APD90 by 12.4% (n=5, P>0.05), 17.6% (n=5, P<0.01), 26.4% (n=5, P<0.01), respectively. GB increased IK in a concentration-dependent manner. GB 0.1, 1, and 10 micromol/L increased IK by 20.1% (n=6, P<0.05), 43.1% (n=6, P<0.01), 55.6% (n=6, P<0.05); increased IK tail by 10.7% (n=6, P<0.05), 25.1% (n=6, P<0.05), and 37.7% (n=6, P<0.05), respectively at testing potential of +50 mV and shift the I-V curve of IK upward. But GB had no significant effect on I(Ca-L) at above concentrations. CONCLUSION: GB significantly shortened APD in a concentration-dependent manner which mainly due to increase of IK.
Subject(s)
Calcium Channels, L-Type/drug effects , Calcium/metabolism , Diterpenes/pharmacology , Lactones/pharmacology , Myocytes, Cardiac/metabolism , Potassium Channels, Voltage-Gated , Potassium Channels/drug effects , Action Potentials/drug effects , Animals , Delayed Rectifier Potassium Channels , Diterpenes/isolation & purification , Ginkgo biloba/chemistry , Ginkgolides , Guinea Pigs , Heart Ventricles/cytology , Lactones/isolation & purification , Male , Myocytes, Cardiac/physiology , Patch-Clamp Techniques , Plants, Medicinal/chemistryABSTRACT
AIM: To observe the effect of LPC on the pacemaker current I(f) in ischemic myocardium and if the effect could be reversed by ISO. METHODS: By using two microelectrode voltage clamp technique to measure and compare the amplitude of I(f) of ischemic myocardium in the presence of LPC and LPC add ISO. RESULTS: Ischemia decreased the amplitude of I(f) at all membrane potential levels. Adding LPC 2 x 10(-5) mol/L to the ischemia-like solution, the amplitude of I(f) decreased further (n = 5, P < 0.05), it means that LPC aggravated the inhibitory effect of "ischemia" on the pacemaker activity. Adding LPC 2 x 10(-5) mol/L and ISO 1 x 10(-6) mol/L together to the ischemia-like solution, the amplitude of I(f) increased significantly at membrane potential -90 mV to - 120 mV (n = 8, P < 0.05) compared with ischemia condition, but still did not reach the levels before ischemia. CONCLUSION: In acute myocardial ischemia condition, toxic metabolite LPC accentuated its inhibitory effect on pacemaker current I(f), a local release and accumulation of catecholamine could not completely reverse their inhibitory effect.
Subject(s)
Isoproterenol/metabolism , Lysophosphatidylcholines/pharmacology , Membrane Potentials/drug effects , Myocardial Ischemia/physiopathology , Animals , Microelectrodes , Myocardial Ischemia/metabolism , Myocardium , Patch-Clamp Techniques , SheepABSTRACT
AIM: To study the effect of ginkgolide B from Ginkgo leave on action potential (AP), L-type calcium current (I(Ca) - L) and delayed rectifier potassium current (I(K)) in normal and ischemic guinea pig ventricular myocytes. METHODS: With the standard microelectrode technique to record action potential and whole-cell variant patch-clamp technique to record calcium and potassium current. RESULTS: (1) Under normal condition, ginkgolide B shortened APD and had no effect on RP, AP and V(max). Ginkgolide B also increased I(K) in a concentration dependent manner and had no significant effect on I(Ca) - L (2) Under ischemia condition, it was observed that shortening of APD, APA, decrease V(max) and depolarization of RP was induced by ischemia, but ginkgolide B could attenuate above--mentioned changes. (3) Under ischemia condition, I(Ca) - L and I(K) were inhibited, perfusion with ischemia solution containing ginkgolide B could reverse the decrease of I(Ca) - L and I(K). CONCLUSION: Ginkgolide B had protective effect on ischemic myocardium to prevent ischemic arrhythmia.
Subject(s)
Action Potentials/drug effects , Ginkgolides/pharmacology , Lactones/pharmacology , Myocardial Ischemia/metabolism , Myocytes, Cardiac/drug effects , Animals , Calcium Channels, L-Type/drug effects , Delayed Rectifier Potassium Channels/drug effects , Guinea Pigs , Heart Ventricles/drug effects , Myocytes, Cardiac/metabolism , Patch-Clamp TechniquesABSTRACT
With whole-cell variant patch-clamp and laser scanning confocal microscope technique, we examined the effect of ginkgolide B (GB) from ginkgo leaves on L-type calcium current and cytosolic [Ca(2+)](i) in guinea pig ischemic ventricular myocytes. The results showed that under normal conditions, at a test voltage of 0 mV, GB had no significant effect on I(Ca,L); and during ischemia, the peak Ca(2+) current reduced by 37.71%, and the I-V curve of I(Ca,L) was shifted upward. 1 micromol/L GB reversed the change induced by ischemia, a result being significantly different from those of the ishemia group (P<0.05).Under control condition, 0.1,1,10 micromol/L GB decreased intracellular calcium concentration by 10.58%, 17.27% and 16.35% (n=12, 12, 10, P<0.01-0.001), respectively. With perfusion of ischemic solution for 12 min, intracellular calcium concentration increased by 20.15%. After a 12 min-perfusion of ischemic solution containing 1 micromol/L nifedipine or 5 mmol/L NiCl2, intracellular calcium concentration increased by 18.18% (P>0.05 vs ischemia) and 11% (P<0.05 vs ischemia), respectively. After 12 min of perfusion with ischemic solution containing 1 micromol/L GB, intracellular calcium concentration increased by 9.6% (P<0.05 vs ischemia). It is shown that GB could reverse the decrease of I(Ca,L) and partially inhibit calcium overload during ischemia.
