Effects of veratrine and paeoniflorin on isolated mouse vas deferens

In vivo microdialysis and in vitro HPLC analysis of the impact of paeoniflorin on the monoamine levels and their metabolites in the rodent brain

Background: Paeoniflorin (PF) possesses several effects such as analgesic, the anti-spasmodic effect on smooth muscle. It protects the cardiovascular system and reveals the neuroprotective effect on cerebral ischemia. Monoamine system has been identified to have complex regulatory effects in pain signaling. There are no reports regarding the impact of PF on monoamine levels in the rodent brain by microdialysis. In this study, the effects of PF on monoamines and their metabolites in the rodent brain using in vivo microdialysis and in vitro high performance liquid chromatography (HPLC) analysis.

Methods: Male S.D. rats were anesthetized, fixed onto the stereotaxic instrument to identify the positions of corpus striatum and cerebral cortex. Drilled a hole in the skull of anesthetic rats and proceeded microdialysis, and gave PF (100 μg, i.c.v.). Collected the dialysate and the concentration of monoamines and their metabolites in dialysate and analyzed with HPLC-ECD. Male ICR mice were administered with PF (96 μg, i.c.v.) and with Ringer solution as a control. After 20 mins of administration, the mice were cut off the brain immediately and separated into eight regions according to the method of Glowinski. Added extraction solution to each region, homogenized and extracted for further procedure. The extract was centrifuged, sucked the transparent layer and centrifuged once more. The transparent layer was filtered with a 0.22 μm nylon filter and analyzed with HPLC-ECD (electrochemical detection).

Results: PF increased the content of DOPAC and NE in the cortex, and increased the content of NE and decreased the content of 5-HT in the medulla of the homogenized mice brain tissue. By microdialysis, PF increased the content of DOPAC and 5-HIAA in anesthetic rat cortex and expanded the content of DOPAC, HVA, and 5-HIAA in anesthetic rat striatum.

Conclusions: It reveals that PF could activate the release of monoamines and increase their metabolites in the rodent brain.

Actions of veratridine on tetrodotoxin-sensitive voltage-gated Na currents, Na1.6, in murine vas deferens myocytes

BACKGROUND AND PURPOSE

The effects of veratridine, an alkaloid found in Liliaceae plants, on tetrodotoxin (TTX)-sensitive voltage-gated Na(+) channels were investigated in mouse vas deferens.

EXPERIMENTAL APPROACH

Effects of veratridine on TTX-sensitive Na(+) currents (I(Na)) in vas deferens myocytes dispersed from BALB/c mice, homozygous mice with a null allele of Na(V)1.6 (Na(V)1.6(-/-)) and wild-type mice (Na(V)1.6(+/+)) were studied using patch-clamp techniques. Tension measurements were also performed to compare the effects of veratridine on phasic contractions in intact tissues.

KEY RESULTS

In whole-cell configuration, veratridine had a concentration-dependent dual action on the peak amplitude of I(Na): I(Na) was enhanced by veratridine (1-10 microM), while higher concentrations (> or =30 microM) inhibited I(Na). Additionally, two membrane current components were evoked by veratridine, namely a sustained inward current during the duration of the depolarizing rectangular pulse and a tail current at the repolarization. Although veratridine caused little shift of the voltage dependence of the steady-state inactivation curve and the activation curve for I(Na), veratridine enhanced a non-inactivating component of I(Na). Veratridine caused no detectable contractions in vas deferens from Na(V)1.6(-/-) mice, although in tissues from Na(V)1.6(+/+) mice, veratridine (> or =3 microM) induced TTX-sensitive contractions. Similarly, no detectable inward currents were evoked by veratridine in Na(V)1.6(-/-) vas deferens myocytes, while veratridine elicited both the sustained and tail currents in cells taken from Na(V)1.6(+/+) mice.

CONCLUSIONS AND IMPLICATIONS

These results suggest that veratridine possesses a dual action on I(Na) and that the veratridine-induced activation of contraction is induced by the activation of Na(V)1.6 channels.

Inhibitory action of L-type Ca2+ current by paeoniflorin, a major constituent of peony root, in NG108-15 neuronal cells

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 microM) 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 I(Ca,L) was 14 microM. However, neither adenosine deaminase (1 U/ml) nor 8-cyclopentyl-1, 3-dipropylxanthine (10 microM) could reverse the inhibition by paeoniflorin of I(Ca,L). Paeoniflorin (30 microM) shifted the steady-state inactivation curve of I(Ca,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 I(Ca,L) exhibited tonic and use-dependent characteristics. Paeoniflorin could effectively suppress I(Ca,L) evoked by action potential waveforms. Paeoniflorin at a concentration of 30 microM 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.