Na⁺/H⁺ exchanger inhibitor cariporide attenuates the mitochondrial Ca²⁺ overload and PTP opening

Abstract

The Na(+)/H(+) exchanger (NHE) inhibitor cariporide has a cardioprotective effect in various animal models of myocardial ischemia-reperfusion. Recent studies have suggested that cariporide interacts with mitochondrial Ca(2+) overload and the mitochondrial permeability transition (MPT); however, the precise mechanisms remain unclear. Therefore, we examined whether cariporide affects mitochondrial Ca(2+) overload and MPT. Isolated adult rat ventricular myocytes were used to study the effects of cariporide on hypercontracture induced by ouabain or phenylarsine oxide (PAO). Mitochondrial Ca(2+) concentration ([Ca(2+)](m)) and the mitochondrial membrane potential (DeltaPsi(m)) were measured by loading myocytes with rhod-2 and JC-1, respectively. We also examined the effect of cariporide on the MPT using tetramethylrhodamine methyl ester (TMRM) and oxidative stress generated by laser illumination. Cariporide (1 microM) prevented ouabain-induced hypercontracture (from 40 +/- 2 to 24 +/- 2%, P < 0.05) and significantly attenuated ouabain-induced [Ca(2+)](m) overload (from 149 +/- 6 to 121 +/- 5% of the baseline value, P < 0.05) but did not affect DeltaPsi(m). These results indicate that cariporide attenuates the [Ca(2+)](m) overload without the accompanying depolarization of DeltaPsi(m). Moreover, cariporide increased the time taken to induce the MPT (from 79 +/- 11 to 137 +/- 20 s, P < 0.05) and also attenuated PAO-induced hypercontracture (from 59 +/- 3 to 50 +/- 4%, P < 0.05). Our data indicate that cariporide attenuates [Ca(2+)](m) overload and MPT. Thus these effects might potentially contribute to the mechanisms of cardioprotection afforded by NHE inhibitors.

Excessive Na+/H+ Exchange in Disruption of Dendritic Na+ and Ca2+ Homeostasis and Mitochondrial Dysfunction following in Vitro Ischemia

“…Interestingly, when either NHE-1, p90 RSK , or NCX rev was inhibited during 60-min REOX, loss of ⌿ m and Ca 2ϩ m accumulation in dendrites was significantly reduced. This finding is consistent with the earlier reports on NHE-1 inhibition-induced attenuation of the mitochondrial Ca 2ϩ overload and mitochondrial permeability transition pore opening in cardiomyocytes and in ischemic/reperfused rat hearts (43)(44)(45). Taken together, these studies demonstrate a conserved role of the NHE-1 signaling mechanism in ischemic reperfusion injury among multiple cell types.…”

Amiloride attenuates lipopolysaccharide-accelerated atherosclerosis via inhibition of NHE1-dependent endothelial cell apoptosis

“…The activation of NHE1 increases Na + i , which leads to intracellular Ca 2+ overload via the Na + /Ca 2+ exchanger and plays a crucial role in many diseases, including ischemia [21] and atherosclerosis [22] . We further investigated whether the activation of NHE1 by LPS resulted in increased intracellular calcium levels.…”

Na+/H+exchange inhibitor cariporide attenuates skeletal muscle infarction when administered before ischemia or reperfusion

“…Specifically, in sustained ischemia, mitochondrial ATP synthesis ceases and glycolysis ensues, resulting in a net breakdown of ATP and an accumulation of lactate and intracellular H ϩ (9 (11,16,51,52,63). If these events continue, the cytosolic Ca 2ϩ will be overloaded, and significant uptake of Ca 2ϩ from the cytosol to the mitochondria will occur, resulting in [Ca 2ϩ ] m overload (55), which can cause cell necrosis (37). However, within 10 -20 min of ischemia, the NHE-1 is inhibited (48) because the extracellular acidosis is more pronounced than the intracellular acidosis (20).…”

“…4). At reperfusion, the rapid washout of extracellular H ϩ after restoration of blood supply may reactivate NHE-1 and further result in accumulation of intracellular Na ϩ and Ca 2ϩ ion influx through reversal of NHE-1, causing intracellular and mitochondrial Ca 2ϩ overload (11,16,51,52,63), which impairs ATP synthesis at the early stage of reperfusion (37,55). Indeed, there are publications that demonstrate effective cardioprotection in the pig (44), dog (19,20), and rabbit (5, 36) when NHE-1 inhibitor is administered intravenously at the onset of ischemia or reperfusion.…”

“…At reperfusion, the rapid washout of the extracellular H ϩ reactivates the NHE-1, resulting in further accumulation of intracellular Na ϩ , causing cytosolic Ca 2ϩ overload through the Na ϩ /Ca 2ϩ activity (12,51). Cytosolic Ca 2ϩ overload is believed to cause mitochondrial Ca 2ϩ overload, which impairs ATP synthesis (37,55). Based on the above sequence of events, it can be speculated that the NHE-1 plays a pivotal role in the pathogenesis of I/R injury.…”