Metabolic compartmentalization in neonatal swine myocytes

Area of Science:

• Biochemistry
• Cellular Physiology
• Cardiovascular Research

Background:

• Metabolite transport across mitochondrial membranes is crucial for cellular energy homeostasis.
• Mitochondrial membrane potential significantly influences metabolite distribution.
• Cardiac muscle cell energy status dictates cytosolic and mitochondrial metabolite concentrations.

Purpose of the Study:

• To investigate metabolic compartmentalization in ventricular myocytes from newborn swine hearts.
• To examine the impact of respiratory inhibition on these metabolic distribution patterns.

Main Methods:

• Isolation of ventricular myocytes from newborn swine hearts.
• Digitoxin fractionation to determine cytosolic and mitochondrial metabolite distribution.
• Measurement of adenine nucleotides (AN), pyridine nucleotides, ATP, and phosphocreatine.
• Assessment of mitochondrial NAD/NADH ratio.
• Use of 3H2O spaces to determine mitochondrial matrix volume.

Main Results:

• Isolated myocytes showed high cytosolic ATP (95%) and AN (86%), with >50% pyridine nucleotides in mitochondria.
• Rotenone treatment maintained ATP levels but decreased phosphocreatine by 50% and mitochondrial NAD/NADH ratio significantly.
• Cytosolic pyridine nucleotides remained highly oxidized despite rotenone.
• Total nucleotide content and compartmentalization were unaffected by respiratory inhibition.
• Mitochondria constitute approximately 30% of total myocyte protein and 29% of the aqueous matrix volume.

Conclusions:

• Newborn swine ventricular myocytes exhibit distinct cytosolic and mitochondrial metabolite compartmentalization.
• Metabolite compartmentalization is resilient to acute respiratory inhibition, suggesting robust regulatory mechanisms.
• Mitochondrial volume and protein content are consistent with values from other species and age groups.