Chloride distribution and exchange in rat ventricle

Area of Science:

• Physiology
• Cardiovascular Research
• Ion Transport

Background:

• Accurate measurement of cellular chloride ([Cl]cell) is crucial for understanding cardiac electrophysiology.
• Previous estimates of myocardial [Cl]cell may have been overestimated due to analytical errors.

Purpose of the Study:

• To accurately determine the cellular chloride content and concentration in the rat left ventricle in vivo.
• To quantify the cellular uptake and efflux of 36Cl in myocardial tissue.
• To characterize the kinetics and temperature dependence of chloride exchange flux in the heart.

Main Methods:

• In vivo measurement of cellular chloride content and 36Cl uptake in rat left ventricles.
• In vitro measurement of 36Cl efflux from perfused, contracting rat ventricles at varying temperatures (22, 30, 38°C).
• Calculation of chloride equilibrium potential and analysis of chloride exchange flux kinetics.

Main Results:

• Cellular chloride concentration ([Cl]cell) was determined to be 8.2 ± 0.5 mmol/kg cell water, lower than prior estimates.
• The calculated chloride equilibrium potential ranged from -70 to -80 mV.
• Chloride exchange flux at 38°C was measured at 31.2 µmol/(g dry ventricle·min), with an apparent activation energy of 10.4 kcal/mol; no dependence on contraction frequency was observed at 22°C.

Conclusions:

• The study provides a more accurate measurement of myocardial cellular chloride concentration.
• The determined chloride flux is among the fastest known ion transport processes in the myocardium.
• These findings have implications for understanding chloride's role in cardiac electrophysiology and potential disease states.