Abstract

The effect of the natural bioflavonoid quercetin on voltage operated calcium channels was investigated in American cockroach (Periplaneta americana) fast depressor motoneuron (Df) using electrophysiological and pharmacological methods. For blockade of outward potassium currents, tetraethylammonium and cesium leakage from microelectrode tip was used. Under this condition and application of command potentials, current-potential relationship was obtained in the absence and presence of quercetin (10 µM). Meanwhile, frequency and amplitude of action potentials (calcium spikes) under current clamp were also determined. In the presence of quercetin, inward calcium current showed a significant increase (p<0.05-0.01) in the potential range of -40 to 0 mV as compared to vehicle. Meanwhile, the frequency of calcium spikes in the presence of quercetin significantly increased relative to vehicle (p<0.01) and quercetin did not significantly change their amplitude. On the other hand, it caused a significant reduction of afterhyperpolarization (AHP) (p<0.05). Quercetin also shifted the voltage dependence of the inactivation and activation curves to more negative potentials and caused a signicant increase in the slope of activation, which reflects a yield of more current for a given potential. Quercetin through augmentation of inward calcium currents (Ica, L), increasing frequency of calcium spikes, and reduction of AHP amplitude could increase excitability and firing of Df motoneurons and this may be of benefit in those brain diseases in which neuronal excitability is depressed.

Key words: Quercetin, calcium channel, electrophysiology, Periplaneta americana.