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 (INa) 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 INa and improve cell survival in a concentration-dependent manner. POP concentration of 0.5 mg mL−1 reduced the amplitude of INa, suppressed the INa of steady-state activation, shifted the steady-state inactivation curves of INa to negative potentials, prolonged the time course of INa recovery from inactivation, and enhanced the activity-dependent attenuation of INa. Furthermore, 0.5 mg mL−1 POP or low concentration of tetrodotoxin (TTX, a VGSC-specific blocker) partially inhibited INa 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 INa channel is strongly recommended.