Inhibition of Na+/H+ exchange preserves viability, restores mechanical function, and prevents the pH paradox in reperfusion injury to rat neonatal myocytes.

Abstract

Rat neonatal myocytes exposed to 2.5 mM CaCN and 20 mM 2-deoxyglucose at pH 6.2 (chemical hypoxia) quickly lose viability when pH is increased to 7.4, with or without washout of inhibitors--a 'pH paradox'. In this study, we evaluated the effect of two Na+/H+ exchange inhibitors (dimethylamiloride and HOE694) and a Na+/Ca2+ exchange inhibitor (dichlorobenzamil) on pH-dependent reperfusion injury. Intracellular free Ca2+ and electrical potential were monitored by laser scanning confocal microscopy of rat neonatal cardiac myocytes grown on coverslips and co-loaded with Fluo-3 and tetramethylrhodamine methylester. After 30-60 min of chemical hypoxia at pH 6.2, mitochondria depolarized and Ca2+ began to increase uniformly throughout the cell. Free Ca2+ reached levels estimated to exceed 2 microM by 4 h. Washout of inhibitors at pH 7.4 (reperfusion), with or without dichlorobenzamil, killed most cells within 60 min, despite a marked reduction of Ca2+ in dichlorobenzamil-treated cells. Reperfusion at pH 7.4 in the presence of 75 microM dimethylamiloride or 20 microM HOE694, or at pH 6.2, prevented cell death. HOE694-treated cells placed into culture medium recovered mitochondrial membrane potential. In most cells, this occurred before normal Ca2+ was restored. Contracted myocytes re-extended over a 24-h-period. By 48 hours, most cells contracted spontaneously and showed normal Ca2+ transients. Our results indicate that Na+/H+ exchange inhibition protects against pH-dependent reperfusion injury and facilitates full recovery of cell function.

• Authors: I S Harper, J M Bond, E Chacon, J M Reece, B Herman, J J Lemasters
• Journal: Basic research in cardiology (Basic Res Cardiol) 1993 Sep-Oct Vol. 88 Issue 5 Pg. 430-42 ISSN: 0300-8428 [Print] Germany
• PMID: 8117249 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S., Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Aniline Compounds
• Carrier Proteins
• Guanidines
• Sodium-Calcium Exchanger
• Sodium-Hydrogen Exchangers
• Sulfones
• Xanthenes
• 3',4'-dichlorobenzamil
• 3-methylsulfonyl-4-piperidinobenzoyl guanidine
• Fluo-3
• 5-dimethylamiloride
• Amiloride
• DNA
• Calcium

Topics

• Amiloride (analogs & derivatives, pharmacology)
• Aniline Compounds
• Animals
• Animals, Newborn
• Calcium (metabolism)
• Carrier Proteins (antagonists & inhibitors, metabolism)
• Cell Survival
• DNA (pharmacology)
• Electrophysiology
• Guanidines (pharmacology)
• Hydrogen-Ion Concentration
• Hypoxia (metabolism)
• Myocardial Ischemia (metabolism, pathology, physiopathology)
• Myocardial Reperfusion Injury (metabolism, pathology)
• Myocardium (metabolism, pathology)
• Rats
• Sodium-Calcium Exchanger
• Sodium-Hydrogen Exchangers (antagonists & inhibitors, metabolism)
• Sulfones (pharmacology)
• Xanthenes