Sodium-dependent potassium channels in leech P neurons

Area of Science:

• Neuroscience
• Cellular Physiology
• Ion Channel Function

Background:

• The Na(+)-K(+) pump is crucial for maintaining membrane potential and ion gradients.
• In leech P neurons, inhibiting the Na(+)-K(+) pump does not depolarize the membrane as expected, suggesting compensatory mechanisms.
• Previous studies indicated an increase in K(+) conductance stabilizes membrane potential despite altered ion gradients.

Purpose of the Study:

• To identify the specific ion channels responsible for the increased K(+) conductance in leech P neurons.
• To investigate the role of intracellular sodium concentration ([Na(+)](i)) in regulating membrane potential and input resistance.
• To characterize the properties of the identified channels, including their activation mechanism and potential physiological relevance.

Main Methods:

• Inhibition of the Na(+)-K(+) pump using ouabain and omission of bath K(+).
• Measurement of membrane potential, input resistance (R(in)), and membrane currents.
• Intracellular sodium concentration ([Na(+)](i)) manipulation and ion injection experiments (Na(+) and Li(+)).

Main Results:

• Inhibition of the Na(+)-K(+) pump led to membrane hyperpolarization and decreased R(in) correlating with increased [Na(+)](i).
• Data support the existence of Na(+)-activated K(+) (K(Na)) channels, with a proposed stoichiometry of three Na(+) ions per channel activation.
• K(Na) channels significantly reduced R(in) (over 90% at maximum activation) and were also activated by Li(+).

Conclusions:

• Na(+)-activated K(+) (K(Na)) channels are responsible for stabilizing membrane potential in leech P neurons under conditions of Na(+)-K(+) pump inhibition.
• These channels play a potentially significant role in the physiological function of leech neurons.
• K(Na) channels in these neurons exhibit cross-activation by both Na(+) and Li(+).