Apocynum venetum leaf aqueous extract inhibits voltage-gated sodium channels of mouse neuroblastoma N2A cells

Ethnopharmacological relevance

Apocynum venetum Linn. (Apocynaceae family), also called Luobuma, is a shrub which grows widely in the Xinjiang Autonomous Region of China. Its leaves are used in herbal tea for the treatment of hypertension, anxiety and depression. Animal studies have also shown that Apocynum venetum leaf extract (AVLE) also exerts anti-depressant and anti-anxiety activities. The effects of AVLE on neuronal tissues in vitro are not fully understood.

Materials and methods

Using the whole-cell voltage-clamp method, we studied the effects of AVLE on ion channels in cultured mouse neuroblastoma N2A cells.

Results

AVLE inhibited voltage-gated inward Na⁺ current in a reversible and concentration-dependent manner (half-inhibitory concentration was 18 μg/ml and maximum inhibition at 100 μg/ml). AVLE specifically promoted steady-state inactivation of Na⁺ channels but did not affect voltage-dependence of activation. The inhibitory effect was not use-dependent and was not affected by 300 μM L-NAME, suggesting that NO was not involved in the action of AVLE in neuronal cells. AVLE also had a mild inhibitory effect on voltage-gated K⁺ channels, but did not affect ATP-sensitive K⁺ channels.

Conclusions

Since voltage-gated Na⁺ and K⁺ channels are associated with neuronal excitability and therefore affect neurotransmission, the modulation of neuronal ion channels by AVLE may exert neuropharmacological effects. In particular, the inhibition of voltage-gated Na⁺ currents by AVLE may in part account for the psychopharmacological effects of this herbal remedy.