Tetrandrine inhibits Ca2+-activated chloride channel in cultured human umbilical vein endothelial cells.

AIM: To characterize the electrophysiological and kinetic properties of Ca2+-activated chloride channel (CaCC) in cultured human umbilical vein endothelial cell line (HUVEC), and test the inhibitory effects of tetrandrine (Tet) on CaCC. METHODS: Ca2+-activated Cl- currents (I(Cl,Ca)) were recorded by patch-clamp whole cell configurations. [Ca2+]i was measured via intracellular Fura-2 fluorescence intensities. RESULTS: I(Cl,Ca) was activated by increasing [Ca2+]i via direct elevation of intracellular calcium. I(Cl,Ca) showed an apparent outward rectification properties, and it was activated in a voltage- and calcium-dependent mode. Tet dose-dependently inhibited I(Cl,Ca), the IC50 was (5.2+/-0.4) micromol/L (n=8 cells). Tet suppressed both voltage-dependent and calcium-dependent activation of I(Cl,Ca). The activation time constant was (326+/-12) ms [in the presence of 10 micromol/L Tet, compared to control (175+/-17) ms, at +100 mV], and Ca2+ concentration for half maximal activation was (387+/-61) nmol/L for Tet (compared to control (287+/-36) nmol/L. CONCLUSIONS: Tet effectively blocked I(Cl,Ca), and such effects might be due to its inhibitory effects on the activation process of Ca2+-activated chloride channel.

Inhibitory effects of DDPH on two components of delayed rectifier potassium current in guinea pig ventricular cells.

AIM: To study the effects of 1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxy-phenyl-ethylamino) propane hydro-chloride (DDPH) on the rapidly activating component (I(Kr)), and the slowly activating component (I(Ks)) of the delayed rectifier potassium current (I(K)) in guinea pig ventricular myocytes. METHODS: Whole-cell patch clamp recording techniques. RESULTS: DDPH (0.1-100 micromol/L) blocked the I(Kr) in a concentration-dependent manner. The IC50 (micromol/L) was 6.1 (95 % confidence limits: 2.8-13.5). IC50 (micromol/L) of DDPH blocking I(Ks) was 12.5 (95 % confidence limits: 4.8-32.2). DDPH (10 micromol/L) did not affect activation time constants and the voltage-dependent activation of both I(Kr) and I(Ks), the half-activation voltage (V1/2, mV) and slope factor (k, mV) were I(Kr): -23.5+/-2.4 and 8.1+/-2.2 [in presence of DDPH, P >0.05, compared with control, V1/2 (-21.7+/-0.8) and k (5.9+/-0.8)]; I(Ks): 27.1+/-0.7 and 16.6+/-0.8 [in presence of DDPH, P >0.05, compared with control, V1/2 (27.0+/-0.8) and k (14.9+/-0.9)]. DDPH slightly increased the deactivation time-constant of I(Kr) ( r) and I(Ks) ( s) at low concentration (<10 micromol/L). The inactivation of I(Kr) was significantly accelerated by DDPH. CONCLUSIONS: DDPH inhibited both I(Kr) and I(Ks). The blockade was not due to its influence on activation, but the process of deactivation. The blocking of I(Kr) by DDPH was further associated with its acceleration the channel inactivation.

Myocardial capillary angiogenesis and coronary flow in ischemia tolerance rat by adaptation to intermittent high altitude hypoxia.

AIM: To determine the effects of simulated intermittent high altitude hypoxia adaptation (IHA) on coronary capillary and coronary flow (CF) in rat hearts. METHODS: Model of Langendorf-perfused isolated rat hearts were used to measure CF during ischemia-reperfusion, and immunoperoxidase staining assay and computer-aid morphometry analysis were conducted to determine the myocardial capillary densities. Cyclic GMP (cGMP) level in myocardium was measured by radio-immunoassay. RESULTS: Pre-ischemia level of CF in IHA rats was higher (IHA28 13.4 mL/min+/-1.5 mL/min, IHA42 15.4 mL/min+/-2.0 mL/min, P < 0.01) than that of normoxic rats (11.0+/-0.8) mL/min, and the recovery of CF after ischemia-reperfusion was better in IHA rats. As an adaptive result, the myocardial capillary densities of the left ventricular myocardium in IHA rats were 1.5 times of those in normoxic control rats, but there was no apparent ventricular hypertrophy in IHA rats. Myocardial cGMP content (1.8+/-0.7) nmol/g in IHA rats were increased significantly compared with control rats (1.1+/-0.4) nmol/g, but cGMP level was not altered before and after ischemia-reperfusion in either group. It was also revealed that in isolated rat hearts perfused, myocardial function recovered better in IHA rats than that in normoxic control rats. CONCLUSION: IHA adaptation increased the tolerance of rat hearts against subsequent ischemia-reperfusion injury, and increase in coronary circulation and angiogenesis might be the mechanisms of myocardium protected by IHA.