The effects of paeoniflorin, a glycoside isolated from the root of Paeonia lactiflora, on ion currents in a mouse neuroblastoma and rat glioma hybrid cell line, NG108-15 were investigated. Paeoniflorin (1-300 μM) reversibly produced an inhibition of L-type voltage-dependent Ca2+ current (I Ca,L) in a concentration-dependent manner. Paeoniflorin caused no change in the overall shape of the current-voltage relationship of I Ca,L. The IC50 value of paeoniflorin-induced inhibition of ICa,L was 14 μM. However, neither adenosine deaminase (1 U/ml) nor 8-cyclopentyl-1, 3-dipropylxanthine (10 μM) could reverse the inhibition by paeoniflorin of ICa,L. Paeoniflorin (30 μM) shifted the steady-state inactivation curve of ICa,L to more negative membrane potentials by approximately - 10 mV. It also prolonged the recovery of I Ca,L. The inhibitory effect of paeoniflorin on ICa,L exhibited tonic and use-dependent characteristics. Paeoniflorin could effectively suppress ICa,L evoked by action potential waveforms. Paeoniflorin at a concentration of 30 μM produce a slight inhibition of voltage-dependent Na+ current and delayed rectifier K+ current. Under current-clamp configuration, unlike adenosine, this compound decreased the firing of action potentials. Taken together, this study indicates that paeoniflorin can block L-type Ca2+ channels in NG108-15 cells in a mechanism unlinked to the binding to adenosine receptors. The effects of paeoniflorin on ion currents may partly, if not entirely, contribute to the underlying mechanisms through which it affects neuronal or neuroendocrine function.
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