Modulation of voltage‐gated channel currents by harmaline and harmane

Abstract

1 Harmala alkaloids are endogenous substances, which are involved in neurodegenerative disorders such as M. Parkinson, but some of them also have neuroprotective effects in the nervous system. 2 While several sites of action at the cellular level (e.g. benzodiazepine receptors, 5-HT and GABA A receptors) have been identified, there is no report on how harmala alkaloids interact with voltagegated membrane channels. 3 The aim of this study was to investigate the effects of harmaline and harmane on voltage-activated calcium-(I Ca(V) ), sodium-(I Na(V) ) and potassium (I K(V) )-channel currents, using the whole-cell patchclamp method with cultured dorsal root ganglion neurones of 3-week-old rats. Currents were elicited by voltage steps from the holding potential to different command potentials. 4 Harmaline and harmane reduced I Ca(V) , I Na(V) and I K(V) concentration-dependent (10-500 mM) over the voltage range tested. I Ca(V) was reduced with an IC 50 of 100.6 mM for harmaline and by a significantly lower concentration of 75.8 mM (Po0.001, t-test) for harmane. The Hill coefficient was close to 1. Threshold concentration was around 10 mM for both substances. 5 The steady state of inhibition of I Ca(V) by harmaline or harmane was reached within several minutes. The action was not use dependent and at least partly reversible. 6 It was mainly due to a reduction in the sustained calcium channel current (I Ca (L þ N) ), while the transient voltage-gated calcium channel current (I Ca(T) ) was only partially affected. 7 We conclude that harmaline and harmane are modulators of I Ca(V) in vitro. This might be related to their neuroprotective effects.

Ca V 3.1 is a tremor rhythm pacemaker in the inferior olive

“…S6). To avoid indirect effects that could result from the nonspecific binding of harmaline on other ion channels (23) or an incomplete integrity of patch clamping due to well-developed electrical synapses of IO neurons (22), we measured I T in HEK cells, which express Ca V 3.1 channels (HEK-Ca V 3.1). Consistently, HEK-Ca V 3.1 cells showed reduced I T in the presence of harmaline, although the inhibitory effect was smaller when compared with that found in IO neurons (Fig.…”

Toxic effects of metals: modulation of intracellular calcium homeostasis

“…This is not a general mechanism! We have also shown, that an application of cis-platin to the same cell line (HeLa S3 cells) results in a clear increase of the intracellular calcium concentration even with very low concentrations (1 nM; Splettstoesser and Büsselberg, 2005). But with this metal compound the calcium increase completely depends on the extracellular calcium concentration.…”

“…Recently we also found evidence, that an increase of the intracellular calcium after the application of cis-platin in HeLa-S3 cells is followed by an increase of the calcium level in the stores (Splettstoesser and Büsselberg, 2005) before the total calcium level in the cells decreases during application. This could be interpreted as a clear indication, that the calcium (re-)uptake mechanism -at least at the concentrations used (up to 10 lM cis-platin) were not significantly impaired.…”

Prevention of cell death by the zinc ion chelating agent TPEN in cultured PC12 cells exposed to Oxygen–Glucose Deprivation (OGD)

“…However, more experiments are needed to fully clarify how Zn 2+ influences glutamate signaling pathway and the voltage-dependent outward potassium ion currents related with neuronal death under hypoxic-ischemic condition. In present study, we have used PC12 cells as model of neuronal cells, which have been used extensively as an experimental A c c e p t e d M a n u s c r i p t 4 system to study various aspects of neurons [21][22][23][24]. We first mimicked the hypoxic-ischemic condition of neuron by Oxygen-Glucose Deprivation (OGD) exposure, and then treated the cells with N, N, N', N'-tetrakis (2-pyridylmethy1) ethylenediamine (TPEN), a specific Zn 2+ chelating agent [25].…”