ABSTRACT
AIM:To study the blocking effects of extracellular Cd2+ on the inward rectifier potassium channel (IRK1) expressed in the Xenopus oocytes. METHODS：Two-microelectrode voltage clamp (TEV) method was used. RESULTS：Cd2+ can concentration-, time- and voltage dependently block IRK1 instantaneous currents ( 1.5 ms after voltage applied ) when external Cd2+ concentration is 0, 0.1, 0.15, 0.3, 0.9, 2.7 or 5.4 mmol/L with K+ concentration fixed to 90 mmol/L. Cd2+ almost has no effect on the gating property and outward currents of IRK1. Cd2+ can concentration-dependently increase the normalized conductance of IRK1. IRK1 can not permeate Cd2+ because reverse potential did not change. Three exponential fitting analyze indicates that time constant is not changed with the change in Cd2+ concentration. This shows that the inhibitory effects of Cd2+ may be caused by surface potential or the blocking site of Cd2+ is at the surface of the channel. Because external Cd2+ can not inhibit IRK1 macroscopic currents more powerfully when external Cd2+ concentration is lower. These mean that external Cd2+ does not work through surface potential mechanism.CONCLUSION:Cd2+ is considered as one of the fast open channel blockers of IRK1 and its blocking site is at the surface of the channel.
ABSTRACT
Objective To investigate the effects of quiet respiratory intrathoracic pressure changes on ventricular dimensions and left ventricular systolic function,and to further verify our newly proposed hypothesis of the mechanism of respiratory effects on hemodynamics.Methods Twenty healthy volunteers aged 18 to 40 years average(24?7) years were included.The respiratory curve and electrocardiogram were simultaneously recorded.The interventricular septum movement,ventricular dimensions and ventricular systolic excursions were recorded by two-dimensional and M-mode echocardiography during quiet respiration.The respiratory variations of the above parameters were derived,and the parameters for assessing ventricular systolic function were calculated.Results With quiet respiration,the interventricular septum moved towards the left ventricle on inspiration,and then towards the right ventricle on expiration.The right ventricular diastolic dimension increased significantly on inspiration compared with those on expiration.The opposite changes occurred with left ventricular diastolic dimensions.The left ventricular posterior wall systolic excursion and the left ventricular stroke volume significantly increased during expiration compared with those during inspiration.No significant differences were found in left ventricular ejection fraction and fractional shortening between inspiration and expiration.Conclusions The respiratory intrathoracic pressure change is one of the factors influencing the reciprocal changes of the left and right ventricular parameters related to ventricular dimensions and systolic function.
ABSTRACT
AIM: To study the blocking effects of extracellular Cd 2+ on the inward rectifier potassium channel (IRK1) expressed in the Xenopus oocytes METHODS:Two-microelectrode voltage clamp (TEV) method was used RESULTS:Cd 2+ can concentration-, time- and voltage dependently block IRK1 instantaneous currents ( 1 5 ms after voltage applied ) when external Cd 2+ concentration is 0, 0 1, 0 15, 0 3, 0 9, 2 7 or 5 4 mmol/L with K + concentration fixed to 90 mmol/L Cd 2+ almost has no effect on the gating property and outward currents of IRK1 Cd 2+ can concentration-dependently increase the normalized conductance of IRK1 IRK1 can not permeate Cd 2+ because reverse potential did not change Three exponential fitting analyze indicates that time constant is not changed with the change in Cd 2+ concentration This shows that the inhibitory effects of Cd 2+ may be caused by surface potential or the blocking site of Cd 2+ is at the surface of the channel Because external Cd 2+ can not inhibit IRK1 macroscopic currents more powerfully when external Cd 2+ concentration is lower These mean that external Cd 2+ does not work through surface potential mechanism CONCLUSION: Cd 2+ is considered as one of the fast open channel blockers of IRK1 and its blocking site is at the surface of the channel
ABSTRACT
AIM To study the effect of CGRP on L-type calcium channel current in guinea pig ventricular myocytes under normal and imitating ischemia and hypoxia conditions. METHOD The whole-cell patch clamp recording technique was used. RESULTS When the ventricular cell was held at -40 mV and depolarized to 0 mV, 1?10 -9 、1?10 -8 and 1?10 -7 mol?L -1 CGRP increased I Ca-L from(1 26?0 18)nA ( n =8) to (1 87?0 25)nA ( P