Na⁺-K⁺ pump activation inhibits endothelium-dependent relaxation by activating the forward mode of Na⁺/Ca²⁺ exchanger in mouse aorta

Abstract

pump activation inhibits endothelium-dependent relaxation by activating the forward mode of Na ϩ /Ca 2ϩ exchanger in mouse aorta. Am J Physiol Heart Circ Physiol 289: H2020-H2029, 2005. First published July 1, 2005; doi:10.1152/ajpheart.00908.2004.-The effect of Na ϩ -K ϩ pump activation on endothelium-dependent relaxation (EDR) and on intracellular Ca 2ϩ concentration ([Ca 2ϩ ]i) was examined in mouse aorta and mouse aortic endothelial cells (MAECs). The Na ϩ -K ϩ pump was activated by increasing extracellular K ϩ concentration ([K ϩ ]o) from 6 to 12 mM. In aortic rings, the Na ϩ ionophore monensin evoked EDR, and this EDR was inhibited by the Na ϩ /Ca 2ϩ exchanger (NCX; reverse mode) inhibitor KB-R7943. Monensininduced Na ϩ loading or extracellular Na ϩ depletion (Na ϩ replaced by Li ϩ ) increased [Ca 2ϩ ]i in MAECs, and this increase was inhibited by KB-R7943. Na ϩ -K ϩ pump activation inhibited EDR and [Ca 2ϩ ]i increase (K ϩ -induced inhibition of EDR and [Ca 2ϩ ]i increase). The Na ϩ -K ϩ pump inhibitor ouabain inhibited K ϩ -induced inhibition of EDR. Monensin (Ͼ0.1 M) and the NCX (forward and reverse mode) inhibitors 2Ј4Ј-dichlorobenzamil (Ͼ10 M) or Ni 2ϩ (Ͼ100 M) inhibited K ϩ -induced inhibition of EDR and [Ca 2ϩ ]i increase. KB-R7943 did not inhibit K ϩ -induced inhibition at up to 10 M but did at 30 M. In current-clamped MAECs, an increase in [K ϩ ]o from 6 to 12 mM depolarized the membrane potential, which was inhibited by ouabain, Ni 2ϩ , or KB-R7943. In aortic rings, the concentration of cGMP was significantly increased by acetylcholine and decreased on increasing [K ϩ ]o from 6 to 12 mM. This decrease in cGMP was significantly inhibited by pretreating with ouabain (100 M), Ni 2ϩ (300 M), or KB-R7943 (30 M). These results suggest that activation of the forward mode of NCX after Na ϩ -K ϩ pump activation inhibits Ca 2ϩ mobilization in endothelial cells, thereby modulating vasomotor tone. extracellular potassium; sodium-potassium pump; forward mode of sodium/calcium exchanger; endothelial cells; intracellular calcium THE NA ϩ -K ϩ PUMP and the Na ϩ /Ca 2ϩ exchanger (NCX) have an important role in modulating vascular contractility. Na ϩ -K ϩ pump activation relaxes vascular smooth muscle by hyperpolarizing the membrane potential (19, 24), and Na ϩ -K ϩ pump inhibition contracts vascular smooth muscle through activating the reverse mode of NCX by Na ϩ accumulation in the myoplasm (9, 18).In endothelial cells, the roles of the Na ϩ -K ϩ pump and NCX are unclear and contradictory. It was reported that Na ϩ -K ϩ pump inhibition affects the synthesis or release of endothelium-derived relaxing factor(s) rather than its effector pathway (29). On the other hand, we previously reported that Na ϩ -K ϩ pump activation inhibits Ca 2ϩ mobilization in endothelial cells and thereby endothelium-dependent relaxation (EDR) (26). NCX is thought to contribute to endothelium-dependent control of vascular contractility (6,25,28). These results support the involvement of the reverse mode of NCX in Ca 2ϩ mobilization in e...

Nuclear Na,K-ATPase plays an active role in Nucleoplasmic Calcium Homeostasis*

“…KBR has also been shown to inhibit the forward mode of NCX1 completely at 30-50 mM (Iwamoto et al, 1996;Kim et al, 2005), which is relevant for the present study. We observed a significant decrease in the Ca 2+ transport into the NE lumen upon addition of 50 mM KBR to thapsigargin-pretreated nuclei (Fig.…”

“…Iwamoto et al (Iwamoto et al, 1996) have shown that KBR did not significantly influence the activities of Na + /K + -ATPase and other ion transporters. Although KBR is known to affect other ion pathways at these higher concentrations (Iwamoto et al, 1996;Kim et al, 2005), the simplest explanation for observations in this study is NCX inhibition.…”

Na+/Ca2+ Exchanger Inhibitor Restores Endothelium-dependent Relaxation in Diabetic Rat Aorta

“…Thereby, Na + /Ca 2 + exchanger contributes to local Ca 2 + homeostasis and cellular control of eNOS activity in the endothelium in rat aorta (Ogura et al, 2004). It was reported that Na + /Ca 2 + exchanger contributed to endothelium-dependent control of vascular contractility and Na + /Ca 2 + exchanger might mediate Ca 2 + influx and be involved in the enhanced [Ca 2 + ]i in the hyperglycemic condition (Kim et al, 2005). The present study demonstrated that the inhibition of EDR caused by high glucose was partially improved by KB-R7943 treatment.…”

Na+/Ca2+ EXCHANGER INHIBITOR AMELIORATES IMPAIRED ENDOTHELIUM‐DEPENDENT Na+ RELAXATION INDUCED BY HIGH GLUCOSE IN RAT AORTA

“…Thus, the Na + /Ca 2+ exchanger contributes to local Ca 2+ homeostasis and cellular control of eNOS activity in the endothelium in rat aorta 29 . It was reported that the Na + /Ca 2+ exchanger contributed to endothelium‐dependent control of vascular contractility 30 and that the Na + /Ca 2+ exchanger may mediate Ca 2+ influx and be involved in the enhanced [Ca 2+ ] i under hyperglycaemic conditions 9 …”