Electrogenesis from an ATPase-ATP-sodium pseudo pump

Area of Science:

• Biochemistry
• Membrane Biophysics
• Cellular Physiology

Background:

• Membrane ATPase, particularly Na-K-ATPase, is known to function as a sodium pump, generating electrical responses.
• These responses, including short circuit current and open circuit voltage, are crucial for cellular ion transport and energy transduction.

Purpose of the Study:

• To investigate the electrogenic potential of membranes in response to Adenosine Triphosphate (ATP).
• To determine if electrogenesis can occur independently of ATP hydrolysis, challenging existing models of ATPase function.
• To explore the role of phospholipids in mediating ATP-induced membrane electrical responses.

Main Methods:

• Reconstituting ATPase into artificial lipid membranes.
• Forming membranes solely from phospholipids found in ATPase.
• Measuring short circuit current and open circuit voltage responses to ATP in these reconstituted and phospholipid-only membranes.
• Comparing responses across different acidic phospholipids, notably cardiolipin.

Main Results:

• Electrogenesis (electrical response) was reproduced in lipid membranes containing solubilized ATPase and in membranes composed of ATPase-derived phospholipids.
• The greatest response was observed with cardiolipin, but other acidic phospholipids also elicited a response.
• Electrogenesis occurred without detectable ATP hydrolysis, indicating a surface phenomenon.

Conclusions:

• ATP-induced electrogenesis in membranes can occur independently of ATP hydrolysis.
• This phenomenon is likely a surface effect driven by the alignment of ATP on phospholipids via ion association.
• The findings necessitate caution when interpreting studies on membrane Na-K-ATPase and its incorporation into artificial systems.
• The presence of necessary substances and the observed orientation of ATP on phospholipids in vitro suggest a role for ion association in Na-K-ATPase function within the mitochondrial membrane.