Inward current activated during hyperpolarization in the rabbit sinoatrial node cell

Area of Science:

• Electrophysiology
• Cellular Neuroscience
• Ion Channel Physiology

Background:

• The inward current activated by hyperpolarization (ih) is a key determinant of cellular excitability.
• Distinguishing ih from other currents, like K-current, is essential for understanding its specific physiological roles.

Purpose of the Study:

• To isolate and characterize the properties of the inward current activated by hyperpolarization (ih).
• To elucidate the kinetic properties and voltage dependence of ih.
• To determine the functional significance of ih in pacemaker cells.

Main Methods:

• Electrophysiological recordings to isolate ih from K-current using voltage-clamp techniques.
• Application of Ba2+ to selectively block K-current.
• Analysis of current-voltage relationships and kinetic properties (time constants).
• Modeling the current using Hodgkin-Huxley type kinetics.

Main Results:

• The ih current was successfully isolated and characterized by its unique activation voltage range and Ba2+ sensitivity.
• The reversal potential for ih was determined to be -25 mV.
• Kinetic analysis revealed time constants ranging from 2-4 s at -70 mV, shortening at -10 mV.
• Activation occurred at -50 mV, saturating at -100 mV, with no rectification observed in the fully activated current-voltage relation.
• The current system was well-described by Hodgkin-Huxley type kinetics.

Conclusions:

• The inward current activated by hyperpolarization (ih) exhibits distinct electrophysiological properties, including a specific voltage-dependent activation and reversal potential.
• Hodgkin-Huxley type kinetics accurately describe the behavior of ih.
• While having a minor role in typical action potentials, ih is vital for maintaining the resting membrane potential in pacemaker cells.