Blockade of L-type calcium channel in myocardium and calcium-induced contractions of vascular smooth muscle by CPU 86017.

AIM: To assess the blockade by CPU 86017 on the L-type calcium channels in the myocardium and on the Ca(2+)-related contractions of vascular smooth muscle. METHODS: The whole-cell patch-clamp was applied to investigate the blocking effect of CPU 86017 on the L-type calcium current in isolated guinea pig myocytes and contractions by KCl or phenylephrine (Phe) of the isolated rat tail arteries were measured. RESULTS: Suppression of the L-type current of the isolated myocytes by CPU 86017 was moderate, in time- and concentration-dependent manner and with no influence on the activation and inactivation curves. The IC(50) was 11.5 micromol/L. Suppressive effect of CPU 86017 on vaso-contractions induced by KCl 100 mmol/L, phenylephrine 1 micromol/L in KH solution (phase 1), Ca(2+) free KH solution ( phase 2), and by addition of CaCl(2) into Ca(2+)-free KH solution (phase 3) were observed. The IC(50) to suppress vaso-contractions by calcium entry via the receptor operated channel (ROC) and voltage-dependent channel (VDC) was 0.324 micromol/L and 16.3 micromol/L, respectively. The relative potency of CPU 86017 to suppress vascular tone by Ca(2+) entry through ROC and VDC is 1/187 of prazosin and 1/37 of verapamil, respectively. CONCLUSION: The blocking effects of CPU 86017 on the L-type calcium channel of myocardium and vessel are moderate and non-selective. CPU 86017 is approximately 50 times more potent in inhibiting ROC than VDC.

Puerarin blocks Na+ current in rat ventricular myocytes.

AIM: To study the effect of puerarin (Pue) on Na+ channel in rat ventricular myocytes. METHODS: Whole-cell patch-clamp technique was applied on isolated cardiomyocytes from rats. RESULTS: Pue inhibited cardiac INa in a positive rate-dependent and dose-dependent manner, with an IC(50) of 349 micromol/L. The kinetics of blockage of cardiac sodium channel by Pue resembled the ClassIa/Ic of antiarrhythmic agents. Pue 300 micromol/L did not alter the shape of the I-V curve of INa, but markedly shifted the steady-state inactivation curve of INa towards more negative potential by 15.9 mV, and postponed the recovery of INa inactivation state from (21.9+/-1.6) ms to (54.4+/-3.4) ms (P<0.01). It demonstrated that the steady state of inactivation was affected by Pue significantly. CONCLUSION: Pue protected ventricular myocytes against cardiac damage and arrhythmias by inhibiting recovery from inactivation of cardiac Na+ channels.

Blockade of paeoniflorin on sodium current in mouse hippocampal CA1 neurons.

AIM: To study the blockade of paeoniflorin (Pae) on I(Na) in the acutely isolated hippocampus neurons of mice. METHODS: The whole-cell patch clamp technique was used. RESULTS: Pae inhibited I(Na) in frequency-dependent and concentration-dependent manners, with an IC50 of 271 micromol/L. Pae 0.3 mmol/L shifted the activation potential of the maximal I(Na) from -40 mV to -30 mV, shifted the steady-state activation and inactivation curves toward more positive and negative potentials by 10.8 mV, and 18.2 mV, respectively, and postponed the recovery of I(Na) inactivation state from (4.2+/-0.7) ms to (9.8+/-1.2) ms. CONCLUSION: Pae inhibited I(Na) in mouse hippocampus neurons.