Effects of polysaccharide from Portulaca oleracea L. on voltage-gated Na channel of INS-1 cells.

Our previous work showed that polysaccharide isolated from Portulaca oleracea L. (POP) has an insulinotropic effect. The voltage-gated Na channel (VGSC) in the excitement phase plays an important role. This work aims to study the effect of POP on the voltage-gated Na channel current (I) and its channel dynamic characteristics in insulin-secreting β-cell line (INS-1) cells of rat. Our results revealed that POP can inhibit the amplitude of I and improve cell survival in a concentration-dependent manner. POP concentration of 0.5 mg mL reduced the amplitude of I, suppressed the I of steady-state activation, shifted the steady-state inactivation curves of I to negative potentials, prolonged the time course of I recovery from inactivation, and enhanced the activity-dependent attenuation of I. Furthermore, 0.5 mg mL POP or low concentration of tetrodotoxin (TTX, a VGSC-specific blocker) partially inhibited I and also improved insulin synthesis and cell survival. Collectively, these results revealed that POP protects INS-1 cells and enhances the insulin synthesis in INS-1 cells, and the mechanism through the partial inhibition on I channel is strongly recommended.