Proton-dependent inhibition of the cardiac sodium channel Nav1.5 by ranolazine

Abstract

Ranolazine is clinically approved for treatment of angina pectoris and is a potential candidate for antiarrhythmic, antiepileptic, and analgesic applications. These therapeutic effects of ranolazine hinge on its ability to inhibit persistent or late Na+ currents in a variety of voltage-gated sodium channels. Extracellular acidosis, typical of ischemic events, may alter the efficiency of drug/channel interactions. In this study, we examined pH modulation of ranolazine's interaction with the cardiac sodium channel, Nav1.5. We performed whole-cell path clamp experiments at extracellular pH 7.4 and 6.0 on Nav1.5 transiently expressed in HEK293 cell line. Consistent with previous studies, we found that ranolazine induced a stable conformational state in the cardiac sodium channel with onset/recovery kinetics and voltage-dependence resembling intrinsic slow inactivation. This interaction diminished the availability of the channels in a voltage- and use-dependent manner. Low extracellular pH impaired inactivation states leading to an increase in late Na+ currents. Ranolazine interaction with the channel was also slowed 4–5 fold. However, ranolazine restored the voltage-dependent steady-state availability profile, thereby reducing window/persistent currents at pH 6.0 in a manner comparable to pH 7.4. These results suggest that ranolazine is effective at therapeutically relevant concentrations (10 μM), in acidic extracellular pH, where it compensates for impaired native slow inactivation.

Cationic Modulation of Voltage-Gated Sodium Channel (Nav1.5): Neonatal Versus Adult Splice Variants—1. Monovalent (H+) Ions

“…Acid block of I Na has been studied in native cardiomyocytes, neurons, skeletal muscle as well as recombinantly expressed VGSCs. 24,25,[29][30][31][38][39][40][41][42][43] Consistent with the results presented in this study, two distinct effects of extracellular acidosis on VGSCs have been routinely observed: reduction of G max and depolarization of voltage dependence of channel gating. In addition, effects on slow and use-dependent inactivation, not determined in this study, have been reported for Nav1.2/1.4/1.5.…”

Inhibitory effects of hesperetin on Nav1.5 channels stably expressed in HEK 293 cells and on the voltage-gated cardiac sodium current in human atrial myocytes

“…Frequency-dependent blockage is the most common type of use-dependent blockage reported to be induced by many drugs, such as A-803467 [5] , ranolazine [23] , mexiletine and propafenone [24] , all of which block open sodium channels. Hesperetin-mediated Nav1.5 channel blockage is also frequency-dependent, thus indicating that higher frequencies increase the total amount of time that Nav1.5 channels spend in their open state, in which they can be bound by hesperetin, thereby leading to enhanced blockage, and that hesperetin preferentially binds to Nav1.5 channels when they are in their open state, as do mexiletine and lidocaine [25] .…”

Mechanisms of Sudden Cardiac Death

“…Both reduced ATP and elevated phosphate levels can inhibit Na + /K + ATPase activity, 86, 87 leading to intracellular Na + accumulation. Increased late Na + -currents (late I Na ) also contributes to increased intracellular [Na + ] during myocardial ischemia 88–90 and heart failure. 91 Elevated intracellular [Na + ] leads to increased cytosolic [Ca 2+ ], at least in part, through decreased extrusion of Ca 2+ or through actual Ca 2+ entry with NCX activity in the reverse mode (Na + out and Ca 2+ in).…”

“…88 Myocardial acidosis during ischemia is also known to affect the inactivation states of Na + channel, leading to increased late I Na (Table 1 and Figure 4). 89, 90 Cardiac Na + channels are reported to be modulated by adenosine monophosphate-activated protein kinase (AMPK). AMPK is a serine/threonine kinase that is activated by increased cytosolic AMP/ATP ratio to increase ATP production and decrease ATP consumption, thereby functioning as a master metabolic regulator in cardiac myocytess.…”