Activation of Na+/H+ Exchanger-directed Protein Kinases in the Ischemic and Ischemic-reperfused Rat Myocardium

Andrea N Moor,Xiaohong Tracey Gan,Morris Karmazyn,Larry Fliegel

doi:10.1074/jbc.m100519200

Andrea N Moor, Xiaohong Tracey Gan + Show 2 more

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https://doi.org/10.1074/jbc.m100519200

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Abstract

The activity of the Na(+)/H(+) exchanger has been implicated as an important contributing factor in damage to the myocardium that occurs during ischemia and reperfusion. We examined regulation of the protein in ischemic and reperfused isolated hearts and isolated ventricular myocytes. In isolated myocytes, extracellular signal-regulated kinases were important in regulating activity of the exchanger after recovery from ischemia. Ischemia followed by reperfusion caused a strong inhibitory effect on NHE1 activity that abated with continued reperfusion. Four major protein kinases of size 90, 55, 44, and 40 kDa phosphorylated the Na(+)/H(+) exchanger. The Na(+)/H(+) exchanger-directed kinases demonstrated dramatic increases in activity of 2-10-fold that was induced by 3 different models of ischemia and reperfusion in intact hearts and isolated myocytes. p90(rsk) was identified as the 90-kDa protein kinase activated by ischemia and reperfusion while ERK1/2 was identified as accounting for some of the 44-kDa protein kinase phosphorylating the Na(+)/H(+) exchanger. The results demonstrate that MAPK-dependent pathways including p90(rsk) and ERK1/2 and are important in regulating the Na(+)/H(+) exchanger and show their dramatic increase in activity toward the Na(+)/H(+) exchanger during ischemia and reperfusion of the myocardium. They also show that ischemia followed by reperfusion have important inhibitory effects on Na(+)/H(+) exchanger activity.

Highlights

The Naϩ/Hϩ exchanger isoform 1 (NHE1)1 is an integral membrane protein that exchanges one intracellular proton for one extracellular sodium ion in response to intracellular acidification, thereby regulating internal pH in most mammalian cells [1, 2]
We have shown that mitogen-activated protein kinase (MAPK) (ERKs) are involved in hormonal regulation of activity of the exchanger in skeletal muscle [9] and more recently we have shown that both MAPK (ERKs) and p90rsk are involved in regulation of exchanger activity in the healthy rat myocardium [10]
This indicated that a MAPK (ERK) pathway is partially responsible for facilitating Naϩ/Hϩ exchanger activity during ischemia reperfusion in neonatal ventricular myocytes

Summary

Introduction

The Naϩ/Hϩ exchanger isoform 1 (NHE1) is an integral membrane protein that exchanges one intracellular proton for one extracellular sodium ion in response to intracellular acidification, thereby regulating internal pH (pHi) in most mammalian cells [1, 2]. It is clearly possible that these signaling pathways may play one or more roles in regulation of the exchanger under ischemia and reperfusion conditions especially since MAPK-dependent pathways have been shown to be important in regulation of the Naϩ/Hϩ exchanger in the myocardium [10]. No studies have shown definitively which kinases from the ischemic and reperfused heart phosphorylate the distal amino acids in the carboxyl terminus of the Naϩ/Hϩ exchanger. We examined the ability of multiple protein kinases from ischemic and ischemia-reperfused myocardium to phosphorylate the cytoplasmic domain of the Naϩ/Hϩ exchanger. The results suggest that regulation of the myocardial Naϩ/Hϩ exchanger may be important in mitigating the damaging effects that ischemia and reperfusion have on the myocardium

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