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

Abstract

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

Keywords: Enzyme-linked immunosorbent assay; Insulin-secreting β-cell line cells; Polysaccharide; Tetrodotoxin; Voltage-gated Na(+) channel.