A decrease of both [Ca2+]e and [H+]e produces cell damage in the perfused rat heart

Area of Science:

• Cardiovascular Physiology
• Cellular Biology
• Biochemistry

Background:

• Cell damage in isolated hearts is influenced by extracellular ion concentrations.
• Understanding the mechanisms of cell injury is crucial for cardiac protection.

Purpose of the Study:

• To investigate the role of extracellular calcium ([Ca2+]e) and pH (pHe) in causing cell damage in Langendorff-perfused rat hearts.
• To elucidate the involvement of gap junctions in this process.

Main Methods:

• Langendorff-perfused rat heart model.
• Measurement of lactate dehydrogenase (LDH) release as an indicator of cell damage.
• Perfusion with varying [Ca2+]e and pHe.
• Use of gap junction blockers (heptanol) and polyethylene glycol (PEG6000).
• Intracellular ion concentration ([Ca2+]i, [Na+]i) and pH (pHi) measurements.

Main Results:

• Reduced [Ca2+]e (0.1-0.4 mmol/l) at alkaline pHe (7.7) induced LDH release.
• Normalizing pHe abolished LDH release.
• Heptanol reduced enzyme release, while PEG6000 prevented cell damage.
• Increased buffer capacity or perfusion flow exacerbated cell damage.
• Marked increases in [Ca2+]i and [Na+]i were observed in non-lysed cells under damaging conditions.
• Isolated cardiomyocytes showed decreased [Ca2+]i and negligible LDH release under similar conditions.

Conclusions:

• Cell damage at low [Ca2+]e and alkaline pHe is mediated by Ca2+ overload.
• This overload occurs via Ca2+ influx through gap junctional leaks.
• The intact myocardium environment is critical for observing this phenomenon, unlike isolated cardiomyocytes.