Changes in extracellular calcium activity in cerebral ischaemia

Area of Science:

• Neuroscience
• Physiology
• Biochemistry

Background:

• Ischemia, a condition of reduced blood flow, significantly impacts brain tissue function.
• Maintaining extracellular ion homeostasis is crucial for neuronal activity and survival.
• Previous studies have indicated potential ionic shifts during ischemic events, but precise mechanisms remain under investigation.

Purpose of the Study:

• To investigate the dynamic changes in extracellular potassium (Ke) and calcium (Cae) activities during partial cerebral ischemia in primates.
• To correlate these ion changes with local cerebral blood flow (CBF) and identify thresholds for ionic disturbance.
• To elucidate the relationship between altered ion concentrations and potential underlying mechanisms like membrane permeability changes.

Main Methods:

• Utilized triple-barreled, double-ion-sensitive microelectrodes for simultaneous measurement of Ke and Cae.
• Monitored ion activities in the cerebral cortex of alpha-chloralose-anesthetized primates undergoing induced partial ischemia.
• Correlated measured ion concentrations with local cerebral blood flow (CBF) data.

Main Results:

• Identified a critical CBF threshold of approximately 10 ml/100g/min below which ion homeostasis is disturbed.
• Observed a dramatic increase in extracellular potassium (Ke) and a significant decrease in extracellular calcium (Cae) in ischemic tissue.
• Demonstrated that the fall in Cae closely follows and is associated with the rise in Ke, occurring after Ke reaches approximately 13.4 mM.

Conclusions:

• Partial cerebral ischemia disrupts extracellular ion balance, characterized by elevated Ke and reduced Cae.
• The observed ionic shifts are closely linked to reduced CBF and a critical threshold, suggesting a loss of ion homeostasis.
• The decrease in Cae is likely mediated by increased neuronal membrane permeability, potentially due to depolarization or depleted cellular energy reserves.