The effects of Securidaca longepedunculata root extract on ionic currents and contraction of cultured rat skeletal muscle cells.

The effects of the primary extract roots of Securidaca longepedunculata were tested on sodium, calcium and potassium currents in rat skeletal muscle cells developed in culture. In addition, they were tested on depolarisation-induced contraction and resting intracellular calcium levels. S. longepedunculata extract (10(-6) g/l) increases sodium current at all potentials. No clear effect was observed on calcium current except for a slight increase at negative potentials (-30, -10 mV) revealing a 5 mV shift towards negative potentials of the I(Ca)/V curve, as with potassium current. In contrast, at the same concentration, S. longepedunculata enhanced the contractile response elicited by durable depolarisation. This was not attributable to the slight increase in resting intracellular free calcium concentration which did not change during and following S. longepedunculata application. These results strongly suggest that S. longepedunculata root extract contains one or more components acting on the voltage-sensor of excitation-contraction coupling (dihydropyridine receptors), regardless of its implication as a calcium channel.