Effect of menthol on two types of Ca currents in cultured sensory neurons of vertebrates

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Abstract
The effect of menthol on voltage-dependent Ca currents was investigated in cultured dorsal root ganglion cells from chick and rat embryos. Bath application of menthol (0.1–1 mM) had different effects on the various Ca currents present in these neurons. Below −20 mV, the low threshold Ca currents were reduced in amplitude in a dose-dependent manner by menthol with little changes of their activation kinetics. In contrast to this, the time course of inactivation of the high-threshold Ca currents, activated above −20 mV from a holding potential of −80 mV, was drastically accelerated by external menthol. The action of menthol was unchanged with more positive holding potentials (−50 mV). Thus, a proposed third type of Ca current with transient activation and complete deactivation below −50 mV was either not present or not affected by menthol. Menthol exerted its action only when applied from the outside. Its effect was completely reversible within 15–20 min of wash-out. Our findings are consistent with the idea that menthol acts on two types of Ca channels coexisting on the membrane of cultured sensory neurons. Menthol blocks currents through the low voltage-activated Ca channel, and facilitates inactivation gating of the classical high voltage-activated Ca channel.