Transmembrane resting potential

Inward Rectifier Potassium Channels or Kir Channels are a class of potassium channels generated by tetra-meiic arrangement of one-pore/two-transmembrane helix (1P/2TM) protein subunits, often associated with additional beta-subunits. Kir channels modulate cell excitability, being involved in repolarization of action potentials (see Fig. 1), setting the resting potential (see Fig. 1) of the cell, and contributing to potassium homeostasis. 

The transient change in the transmembrane potential upon excitation. An action potential cycle consists of a transient depolarization of the cell membrane of an excitable cell (such as a neuron) as a result of increased permeability of ions across the membrane, followed by repolarization, hyperpolarization, and finally a return to the resting potential. This cycle typically lasts 1-2 milliseconds and travels along the axon from the cell body (or, axon hillock) to the axonal terminus at a rate of 1-100 meters per second. See Membrane Potential... 

Thus, a 10 1 transmembrane gradient of a single monovalent ion, say potassium, will generate a membrane potential of 58 mV. See Resting Potential Action Potential Depolarization Threshold Potential Nernst Equation Goldman Equation Patch-Clamp Technique... 

Channel activity is best studied electrochemically as charged species cross a cell membrane or artificial lipid bilayer. There is a difference in electrical potential between the interior and exterior of a cell leading to the membrane itself having a resting potential between -50 and -100 mV. This can be determined by placing a microelectrode inside the cell and measuring the potential difference between it and a reference electrode placed in the extracellular solution. Subsequent changes in electrical current or capacitance are indicative of a transmembrane flux of ions. 

The normal cardiac cell at rest maintains a transmembrane potential 80—90 mV negative to the exterior this gradient is established by pumps, especially the Na, K —ATPase, and fixed anionic charges within cells. At rest, the normal cardiac cell is permeable to (because inward rectifier channels are open) and [K] is the major determinant of resting potential. 

Plateau phase, characterized by low membrane conductance and the activation of a slow inward Ca current. Phase 3. Repolarization to resting potential results from outward K current. Phase 4. Outward K current is deactivated and an inward Na+ current reduces transmembrane potential. 

Depolarization Depolarization is a process that is said to occur whenever the transmembrane potential becomes more positive than some resting potential. 

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