Endothelin-1 Stimulates the Na ⁺ /Ca ²⁺ Exchanger Reverse Mode Through Intracellular Na ⁺ (Na ⁺ _i )–Dependent and Na ⁺ _i -Independent Pathways

Abstract

Abstract-This study aimed to explore the signaling pathways involved in the positive inotropic effect (PIE) of low doses of endothelin-1 (ET-1). Cat papillary muscles were used for force and intracellular Na ϩ concentration (Na ϩ i ) measurements, and isolated cat ventricular myocytes for patch-clamp experiments. ET-1 (5 nmol/L) induced a PIE and an associated increase in Na ϩ i that were abolished by Na ϩ /H ϩ exchanger (NHE) inhibition with HOE642. Reverse-mode Na ϩ /Ca 2ϩ exchanger (NCX) blockade with KB-R7943 reversed the ET-1-induced PIE. These results suggest that the ET-1-induced PIE is totally attributable to the NHE-mediated Na ϩ i increase. However, an additional direct stimulating effect of ET-1 on NCX after the necessary increase in Na ϩ i could occur. Thus, the ET-1-induced increase in Na ϩ i and contractility was compared with that induced by partial inhibition of the Na ϩ /K ϩ ATPase by lowering extracellular KIn the presence of HOE642 and after increasing contractility and Na ϩ i by low K ϩ o , ET-1 induced an additional PIE that was reversed by KB-R7943 or the protein kinase C (PKC) inhibitor chelerythrine. ET-1 increased the NCX current and negatively shifted the NCX reversal potential (E NCX ). HOE642 attenuated the increase in NCX outward current and abolished the E NCX shift. These results indicate that whereas the NHE-mediated ET-1-induced increase in Na ϩ i seems to be mandatory to drive NCX in reverse and enhance contractility, Na ϩ i -independent and PKC-dependent NCX stimulation appears to additionally contribute to the PIE. However, it is important to stress that the latter can only occur after the primary participation of the former. Key Words: contraction Ⅲ ion channels Ⅲ endothelin E ndothelin-1 (ET-1) is a powerful inotropic agent that induces this effect acting through different intracellular signaling pathways. 1-4 However, at doses that increase contractility by Ϸ20%, the positive inotropic effect (PIE) is entirely attributable to activation of the reverse mode of the Na ϩ /Ca 2ϩ exchanger (NCX). 5 This increase in contractility is similar in magnitude to that detected during the slow force response of myocardial stretch. 6 -8 A sustained increase in intracellular Ca 2ϩ through the NCX reverse mode induced by an increase in intracellular Na ϩ (Na ϩ i ) produced by the activation of the Na ϩ /H ϩ exchanger (NHE) may represent the signaling link between this transporter and cardiac hypertrophy. 9 -11 In fact, we demonstrated recently that this mechanism is responsible for the increase in contractility induced by ET-1. 5 We proposed that ET-1 activates the NHE, which increases Na ϩ i and shifts the NCX reversal potential (E NCX ) to a more negative voltage. These changes give more time for NCX to operate in reverse mode during the action potential and promote Ca 2ϩ influx to the cell, determining the increase in force. 5 It is well known that activation of protein kinase C (PKC) is a downstream pathway of ET-1 receptor binding. 4 Consistently, it has been shown that PKC phosphoryl...

Phospholipase C-dependent control of cardiac calcium homeostasis involves a TRPC3-NCX1 signaling complex

“…PLC-dependent regulation of the cardiac NCX has previously been reported and attributed to Na + /H + exchanger (NHE1) activity [6]. Indeed, we observed a modest inhibitory effect of the NHE inhibitor Hoechst 943 on reverse mode NCX-mediated Ca 2+ signals (data not shown).…”

“…Ca entry via reverse mode NCX increases substantially when intracellular Na + rises. This may occur as a result of Na + /K + ATPase inhibition [5] or sodium hydrogen exchanger (NHE) mediated Na + increase [6]. Promotion of reverse mode NCX has been suggested for pathophysiological situations such as heart failure [7] or ischemia which are typically associated with increases in intracellular Na + levels [8].…”

The interdependence of endothelin-1 and calcium: a review

“…ET-1 suppresses plasma membrane Calcium-ATPase function and expression in hepatic sinusoidal endothelial fenestrae, leading to contraction [98]. ET-1 also causes the sodium/calcium exchanger (NCX) in the plasma membrane of ventricular myocytes to operate in reverse mode, whereby NCX become calcium influx pumps instead of acting as calcium efflux pumps [99]. Future research is needed to elucidate the physiological effects which can be attributed to prolonged increases in [Ca 2+ ] i by ET-1.…”

The cardiac electrogenic sodium/bicarbonate cotransporter (NBCe1) is activated by aldosterone through the G protein-coupled receptor 30 (GPR 30)

“…4,[21][22][23] The increase in [Na C ] i is crucial for cardiac pathophysiology because, as it is well-known, it decreases the driving force of the forward mode (extruding Ca 2C mode) of the Na C /Ca 2C exchanger (NCXf) or even favors the reverse mode of this transporter (NCXr), leading to an increase in [Ca 2C ] i . [24][25][26] Due to its stoichiometry, the NBCe1 acts as a Na C -sparing transporter, because it needs half amount of Na C to mediate the influx of the same amount of HCO 3 ¡ than the NBCn1. Thus, it could be possible to speculate that the activation of NBCe1 through GPR30 results in a decreased Na C uptake upon defending the cell against intracellular acidosis, explaining at least in part the cardioprotective properties of G1 commented above.…”