NHE-1 and NBC during pseudo-ischemia/reperfusion in rabbit ventricular myocytes

• Published in: Journal of molecular and cellular cardiology Vol. 37; no. 2; pp. 567 - 577
• Main Authors: van Borren, Marcel M.G.J, Baartscheer, Antonius, Wilders, Ronald, Ravesloot, Jan H
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-08-2004
• Subjects: Animals; Heart Ventricles - cytology; Hydrogen - metabolism; In Vitro Techniques; Ischemia; Myocardial Reperfusion Injury - metabolism; Myocytes; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - metabolism; Na+- HCO3- cotransport; Na/H exchanger; Rabbits; Reperfusion; Sodium - metabolism; Sodium Cyanide - pharmacology; Sodium-Bicarbonate Symporters - metabolism; Sodium-Hydrogen Exchangers - metabolism; Reperfusion; Myocytes; Ischemia; Na/H exchanger; Na +- HCO 3 - cotransport
• ISSN: 0022-2828; 1095-8584
• DOI: 10.1016/j.yjmcc.2004.05.017

Despite many studies into the pathophysiology of cardiac ischemia–reperfusion injury, a number of key details are as yet undisclosed. These include the timing and magnitude of the changes in both Na
+/H
+ exchange (NHE-1) and
Na
+-
HCO
3
--cotransport (NBC) transport rates. We fluorimetrically measured
H
i
+ fluxes (
J
NHE-1 and
J
NBC) and
Na
i
+ fluxes in single contracting rabbit ventricular myocytes subjected to metabolic inhibition, pseudo-ischemia (i.e. metabolic inhibition and extracellular acidosis of 6.4), and pseudo-reperfusion. Metabolic inhibition and pseudo-ischemia inhibited NHE-1 by 43 ± 3.1% and 91 ± 3.6%, and NBC by 66 ± 5.4% and 100%, respectively. Inhibition was due to both an acidic shift of the pH
i at which NHE-1 and NBC become quiescent (set-point pH
i) and a reduction of the steepness of the
pH
i
-
H
i
+ flux profiles. NHE-1 and NBC did not contribute to
Na
i
+ loading during metabolic inhibition (
Na
i
+ 18 ± 1.7 mM) or pseudo-ischemia (
Na
i
+ 21 ± 1.7 mM), because pH
i acidified less than set-point pH
i's. Upon pseudo-reperfusion NBC recovered to 54 ± 7.3% but NHE-1 to 193 ± 11% of aerobic control flux, and set-point pH
i's returned to near neutral values. Metabolic inhibition and reperfusion caused an acid load of 18 ± 3.2 mM H
+ 94% of which were extruded by the hyperactive NHE-1. At pseudo-reperfusion
Na
i
+ rose sharply to 31 ± 5.8 mM within 1.5 min and that coincided with hypercontracture. Cariporide not only prevented the
Na
i
+ transient, but also inhibited pH
i recovery and prevented hypercontracture. Our results are consistent with the view that NHE-1 is active during metabolic inhibition if, like in whole hearts, pH
i is driven more acidic than NHE-1 set-point pH
i. Furthermore, either an acidic pH
i or absence of additional
Na
i
+ loading during reperfusion, or both, limit ischemia–reperfusion injury.