Ca-activated potassium current in vertebrate sympathetic neurons

Area of Science:

• Neuroscience
• Electrophysiology
• Ion Channels

Background:

• Sympathetic neurons possess calcium-activated potassium currents (IC).
• These currents are influenced by intracellular calcium levels and voltage changes.

Purpose of the Study:

• To characterize the biophysical properties of calcium-activated potassium currents (IC) in sympathetic neurons.
• To investigate the voltage-dependence and kinetics of IC.
• To explore the functional role of IC in neuronal excitability.

Main Methods:

• Intracellular calcium injection and activation of voltage-gated calcium channels (ICa) to trigger IC.
• Voltage-clamp recordings to measure IC.
• Relaxation, fluctuation, and single-channel analysis.
• Blockade with tetraethylammonium (TEA).

Main Results:

• IC is strongly voltage-dependent, with a peak slope of 11 mV/e-fold depolarization above -50 mV.
• Channel opening and closing rates are voltage-dependent, with time constants around 15 msec near 0 mV.
• Single channel conductance is approximately 100 pS.
• IC activates rapidly (≤ 5 msec) and can be transient.
• TEA effectively blocks IC.
• Spontaneous miniature ICs were observed, likely due to localized calcium release.

Conclusions:

• IC in sympathetic neurons exhibits distinct voltage-dependent properties and rapid kinetics.
• These currents are crucial for regulating sympathetic neuronal activity, contributing to spike repolarization and after-hyperpolarization.
• The findings provide insights into the physiological roles of IC in neuronal function.