The Na+-K+ ATPase Pump

Cardiac glycosides:

plant and animal steroids Ouabain!

Digitalis!: increased Na+ conc inside heart leads to stimulation of Na+-Ca2+ exchanger, which extrudes sodium in exchange for inward movement of calcium. Increased intracellular Calcium stimulates muscle contraction.

The Na+-K+ ATPase Pump: Mechanism

Response of a human RBC to changes in osmolarityof the extracellular fluid

The Na+-K+ ATPase Pump is required to maintain Osmotic Balance and Stabilize Cell Volume

Sources of Intracellular Osmolarity:

large number of counterions (inorganic ions of opposite charge) that are attracted to large macromolecules (most are charged).

small metabolites (high concentration of small organic molecules, sugars, amino acids, nucleotides) and their counterions

Sources of Extracellular Osmolarity:

Due mainly to small inorganic ions - these leak slowly across the plasma membrane into the cell.

The problem:

Because of above factors, water moves into the cell by osmosis

The Solution: Na+-K+ ATPase Pump

In vitro Investigation of The Na+-K+ ATPase Pump

Control of acid secretion in the stomach

Potassium channel

The Potassium Channel

Hinge-bending Model for the opening of the Bacterial KcsA Channel.

The Structure of One subunit of a eukaryotic, Voltage Gated K+ Channel

(Drosophila Shaker K+ Channel)

3-D Structure of a Voltage Gated Mammalian K+ Channel

Conformational States of a Voltage Gated K+ Ion Channel

A typical ion channel fluctuates between open and closed states

The gating of ion channels

The technique of patch clamp recordingMeasuring Ion Channel Conductance

Patch Clamp Recording

Patch Clamp Recording

The ionic basis of membrane potential

The membrane potential in animal cells depends mainly on K+ Leak channels and

the K+ gradient across the plasma membrane

Gconc= -RT ln [Co] [Ci]

Gvolt=zFV

Gconc + Gvolt = 0

Ion distribution is at equilibrium across the membrane

The Nernst Equation and Ion Flow

V= RT ln Co zF Ci

The Resting Potential decays only slowly when the Na+ K+ Pump is stopped