Comparative studies on fresh and postmortem isolated synaptosomes: ATPase activities and ouabain binding.

Area of Science:

• Neuroscience
• Biochemistry
• Cell Biology

Background:

• Previous studies confirmed functional and morphological integrity of rat cortical synaptosomes up to 2 hours postmortem.
• This research extends the investigation into the viability of synaptosomes during extended postmortem periods.

Purpose of the Study:

• To assess the functional activity of Na-K-ATPase and Mg-dependent ATPase in postmortem rat cortical synaptosomes.
• To evaluate the binding of ouabain to synaptosomes after prolonged postmortem storage.
• To investigate oxygen consumption patterns in postmortem synaptosomes and their response to metabolic modulators.

Main Methods:

• Isolation of rat cortical synaptosomes at various postmortem time points (up to 6 hours).
• Assay of Na-K- and Mg-dependent ATPase activity.
• Ouabain binding assays.
• Measurement of oxygen consumption, with and without uncouplers like DNP and veratrine.

Main Results:

• Key enzymatic functions, including Na-K-ATPase and Mg-dependent ATPase activities and ouabain binding, remained largely unaltered in synaptosomes stored for up to 6 hours postmortem.
• Oxygen consumption in 6-hour postmortem synaptosomes was significantly reduced and unresponsive to DNP and veratrine.
• A discrepancy was observed between the actual and potential activity of Na-K-ATPase, calculated via oxygen consumption versus phosphate splitting.

Conclusions:

• Rat cortical synaptosomes maintain critical enzymatic functions for at least 6 hours postmortem.
• Extended postmortem storage impacts mitochondrial respiration, leading to decreased and unresponsive oxygen consumption.
• The study highlights a potential limitation in using oxygen consumption alone to fully assess Na-K-ATPase activity in aged synaptosomes.