The Plasma Membrane Cell-Environment Interactions.

The Plasma Membrane

Cell-Environment Interactions

Goals

• Describe the Role of the glycocalyx when the cells interact with their environment

Goals

• Describe the Role of the glycocalyx when the cells interact with their environment

• Describe the roles of the membrane receptor and voltage sensitive membrane channel proteins

Interactions

• The cell can interact directly with other cells by direct contact.

• Or indirectly through chemicals such as hormones and neurotransmitters

Interactions

• The glycocalyx is involved in these interactions

Interactions

• The glycocalyx is involved in these interactions• To accomplish this, glycocalyx molecules fall

into two broad categories– Cell adhesion molecules &

Interactions

• The glycocalyx is involved in these interactions• To accomplish this, glycocalyx molecules fall

into two broad categories– Cell adhesion molecules &– Plasma membrane receptors

Role of Cell Adhesion Molecules(CAM)

• Every cell has thousands of CAM proteins.

• CAM’s are classified as– Cadherins &– Integrins

Role of Cell Adhesion Molecules(CAM)

They act as :• Molecular Velcro such as the

desmosomes and other cell attachment points

Role of Cell Adhesion Molecules(CAM)

They act as :• Molecular Velcro such as the

desmosomes• The arms of migrating cells, that

allow cells to pull past each other

Role of Cell Adhesion Molecules(CAM)

They act as :• Molecular Velcro such as the

desmosomes• The arms of migrating cells that

allow cells to pull past each other• SOS signals for broken blood vessels

that attract white blood cells

Role of Cell Adhesion Molecules(CAM)

They act as :• Molecular Velcro such as the

desmosomes• The arms of migrating cells• SOS signals for broken blood vessels that

attract white blood cells• Mechanical stressors that respond to

local tension on the cell surface stimulating or degrading membrane components

Role of Cell Adhesion Molecules(CAM)

They act as :• Molecular Velcro such as the desmosomes• The arms of migrating cells• SOS signals for broken blood vessels that

attract white blood cells• Mechanical stressors that respond to local

tension on the cell surface stimulating or degrading membrane components

• Transmitters of intracellular signals that direct cell migration and proliferation

Role of Membrane Receptors

Glycoproteins can serve as membrane receptors.

There are several types:– Contact signaling receptors– Chemical Signaling receptors – G protein receptors

Role of Membrane Receptors

Contact Signaling Receptors occur when cells come into contact with each other. This is important in normal development and immunity. For example, the histocompatibility markers used in organ tansplants

Role of Membrane Receptors

Chemical signaling represents the most common group.

Ligands, the signaling molecule, binds to a membrane receptor. Examples of ligands include neurotransmitters and hormones.

Role of Membrane Receptors

• Different cells can respond differently to the same ligand

• For example, the neurotransmitter, norepinephrine contracts the smooth muscle in the arteries and dilates the smooth muscle in the bronchi

Role of Membrane Receptors

This is due to how the internal machinery of the cell is attached to the receptor.

This can be accomplished several ways:

Role of Membrane Receptors

This can be accomplished several ways:• By the receptor acting as an enzyme

Role of Membrane Receptors

This can be accomplished several ways:• By the receptor acting as an enzyme• By being a chemically gated channel

where ion gates are open or closed briefly

Role of Membrane Receptors

This can be accomplished several ways:• By the receptor acting as an enzyme• By being a chemically gated channel

where ion gates are open or closed briefly

• Others are coupled to a regulatory molecule called the G protein

The G Protein

The G protein acts as a relay between the receptor and its effector (enzyme or channel)A second messenger is generated to accomplish this.Two major second messengers are cyclic AMP and Ca+2

The G Protein

These second messengers activate protein kinases which go on and activate other enzymes amplifying the effect on the receptor stimulation.

The G Protein

Brugada Syndrome

Brugada Syndrome

• Brugada is a genetic disease characterized by an abnormal EKG that carries an increased risk of sudden death.

• It is a cause of Sudden Adult Death Syndrome (SADS)

• It has been associated with a defect in the sodium ion channel. This can lead to potentially fatal cardiac arrhythmias

Brugada Syndrome

• Warning Signs of SADS• family history of unexpected, unexplained

sudden death under age 40• fainting or seizure during exercise,

excitement or startle• consistent or unusual chest pain and/or

shortness of breath during exercise.

Brugada Syndrome

• It is estimated that over half of the 4,000 SADS deaths each year of children, teens, or young adults have one of the top two warning signs: 1) family history – of a SADS diagnosis or sudden unexplained death (usually undiagnosed and untreated) of a family member, or 2) fainting.