Intracellular pH regulation during prolonged hypoxia in rats

Area of Science:

• Physiology
• Cardiovascular Physiology
• Respiratory Physiology

Background:

• Cellular pH homeostasis is critical for organ function.
• Hypoxia and altered PCO2 challenge acid-base balance.
• Skeletal and cardiac muscles exhibit distinct buffering capacities.

Purpose of the Study:

• To investigate the impact of prolonged hypoxia on intracellular pH (pHi) regulation in rat skeletal and cardiac muscles.
• To determine the role of renal compensation in mediating these effects.
• To compare the buffering responses between different tissues under hypoxic conditions.

Main Methods:

• Rats were exposed to prolonged hypoxia (PB 370-380 Torr, PIO2 68-70 Torr) or normoxia.
• Intracellular pH was measured using the DMO distribution method in ventricle and skeletal muscles.
• Apparent non-bicarbonate buffer value (beta app) was calculated.
• Bilateral nephrectomy was performed in a subset of hypoxic rats.

Main Results:

• Hypoxia significantly increased beta app in plasma and skeletal muscles (tibialis anterior, quadriceps, diaphragm), but not in cardiac ventricles.
• Bilateral nephrectomy in hypoxic rats attenuated the increase in beta app in plasma and skeletal muscles, indicating a renal contribution.
• Ventricular beta app remained unchanged by hypoxia or nephrectomy.

Conclusions:

• Prolonged hypoxia enhances intracellular pH regulation in skeletal muscles, primarily through improved non-bicarbonate buffering and effective renal compensation.
• Cardiac muscle exhibits intrinsic mechanisms for pH regulation that are not influenced by prolonged hypoxia.
• Renal function plays a significant role in adapting skeletal muscle acid-base balance to chronic hypoxic conditions.