APPS November 2002 Meeting Abstract 1105

T.R. Moopanar, X-H. Xiao, D.G. Allen, Institute of Biomedical Research and Department of Physiology, University of Sydney, New South Wales 2006.

Activation of the myocardial Na⁺/H⁺ exchanger (NHE1) during ischemia and/or reperfusion causes an accumulation of intracellular sodium; this causes a calcium influx that is thought to contribute to ischemia and/or reperfusion injury.

There is dispute about the extent of NHE1 activation during ischemia as opposed to reperfusion¹. The objective of the present study was to show that AMP-activated protein kinase (AMPK) activation is involved in the inhibition of NHE1 during ischemia.

Intracellular pH (pH_i) was measured in single rat ventricular myocytes. NHE1 activity was estimated from the acid load caused by 20 mM NH₄Cl removal. When the adenosine analog 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) (0.5 mM), an activator of AMPK, was applied for 20min, we found that the rate of proton extrusion (J_H) was reduced ten-fold (J_H = 0.5 ± 1.8 mM/min) when compared to the control (J_H = 5.33 ± 0.69 mM/min). Furthermore, the effect of AICAR was reversed in the presence of a putative AMPK inhibitor adenine 9-beta-D-arabinofuranoside² (ara-A) (0.5 mM) (J_H = 5.38 ± 1.11 mM/min), when compared to the control (J_H = 4.83 ± 1.08 mM/min). Finally, we applied ara-A to cells undergoing hypoxic stress and found that the metabolic inhibition of NHE1 under hypoxic stress (J_H = 0.41 ± 1.22 mM/min) was reversed in the presence of ara-A (0.5 mM) (J_H = 4.79 ± 1.42 mM/min).

These results provide evidence that AMPK activation during metabolic stress leads to a reduction in NHE1 activity and supports the theory that NHE1 activity is reduced during ischemia.

(2) Musi N, Hayashi T, Fujii N, Hirshman MF, Witters LA, Goodyear LJ. American Journal of Physiology. Endocrinology and Metabolism 2001;280:E677-84.