ABSTRACT
Objective: α-asarone is a major effective component that can be isolated from Acorus tatarinowii Schott,a Chinese herbal medicine. Clinical investigations have shown that α-asarone has strong sedative and anti-convulsive action in the central nervous system. In recent years, several medicines containing a-asarone were applied in treatment of asthma, bronchitis, expectorant, or epilepsy. However, the underlying cellular mechanism of ct-asarone is still unknown. Here the authors considered EAAC1, the transporter for the excitatory glutamate, as a possible target. Methods: Supercritical CO2 fluid extraction and silica gel column chromatography were used to obtain ct-asarone from the rhizomes of Acorus tatarinowii Schott. Xenopus oocytes with heterologously expressed EAAC 1 were used as a model system. Rate of glutamate uptake was measured by means of isotopic tracer technique. Glutamate-induced current was recorded under two-electrode voltage clamp. 40μg/mL of ct-asarone was used for testing its effect on EAAC1 activity. Results: ct-asarone induced a slight, but still significant stimulation of rate of glutamate uptake by 15%. In contrast, EAACl-mediated current became reduced (by 30% at -100 mV). Since EAAC 1 can operate in transport and also in an ion-channel mode, the result indicates strong inhibition of the channel mode. This inhibition is voltage-dependent becoming larger at more negative potentials. Conclusion: The stimulation of glutamate uptake reduces glutamate concentration in the synaptic cleft and, hence, reduces excitatory synaptic activity. The inhibition on the ion-channel mode stabilizes the membrane potential, and therefore, also contributes to reduced excitatory activity.
ABSTRACT
Objective: To investigate the possible mechanisms in acupuncture analgesia by interaction of &opioid receptor with neurotransmitter transport proteins or the Na+-K+pump. Methods: Microinjection of respective heterologous cRNA into the Xenopus oocytes as a model system, and measurement of steady-state currents under two-electrode voltage clamp. Results: The co-expression of the δ-opioid receptor with GAT1, EAAC1 or the sodium pump resulted in reducing activity of the respective transporter. Opioid receptor activation affected transporter activity in different ways: 1) GAT1 was further inhibited; 2) EAAC1 was stimulated; 3) Na+-K+ pump activity interfered with agonist sensitivity of DOR. Pump inhibition led to higher sensitivity for DPDPE. Conclusion: GABA transporter inhibition and glutamate transporter stimulation may counteract pain sensation by affecting the neurotransmitter concentration in the synaptic cleft and, therefore, may contribute synergistically to pain suppression by acupuncture. Sodium pump inhibition by endogenous ouabain may amplify these effects. These synergistic effects may be the molecular mechanism of inhibiting pain sense and/or acupuncture analgesia.