Ranolazine Effects on NaV1.2 and Modulation by pH

Abstract

Ranolazine is an anti-anginal drug previously shown to block persistent currents of the cardiac voltage gated sodium channel, NaV1.5. The effects of ranolazine, however, have not yet been described in all sodium channel isoforms. We studied the effects of ranolazine on the neuronal sodium channel isoform, NaV1.2, and its modulation by extracellular protons. Ionic currents were measured from Chinese Hamster Ovary (CHO) cells expressing the α-subunit of NaV1.2, using whole cell patch clamp techniques. Voltage protocols were run with extracellular solutions of pH 7.4 and pH 6.0 before and after the addition of ranolazine. The addition of 100 μM ranolazine at pH 7.4 led to a significant decrease in late sodium current, faster rate of open state fast inactivation, and slower recovery from inactivation. Similar trends were seen in preliminary experiments at 10 μM and 30 μM ranolazine. In addition, we observed a tonic block of peak current and an increase in total use-dependent block. Many of these effects were different at low pH. Low pH led to a significant depolarizing shift of the conductance curve, and slowed the onset of fast inactivation. Adding ranolazine at pH 6.0 significantly decreased the rate of fast inactivation recovery, and increased the total use-dependent block and rate of open state inactivation. Although directions of the effects were unchanged, the magnitude of these effects was significantly different between the two pH values. Our results suggest that ranolazine stabilizes fast inactivation at both pH 7.4, and pH 6.0. It is possible that ranolazine and protons may compete for a common binding site or indirectly interact leading to decreased ranolazine efficacy at low pH. (Supported by a research grant from Gilead Sciences, Inc. and an NSERC Discovery Grant to PCR, and an NSERC URSA to CHP.)