Cell Communication

Direct contact between cells

Through extracellular chemical messengers

Local Regulators

Gap junctions

Cell-to-cell recognition

• cells are connected by tunnels formed by connexons

  • Allows ions and small water soluble chemicals to pass between cells

  • Cardiac and smooth muscle

• interaction of cell-surface molecules

• Immune cells – recognize self vs. non-self

• Receptors meet glycocalyx

• Cells release ligands that bind to receptors on target cells to initiate a desired cellular response

• Local regulators vs. Long distance regulators

Paracrine

Autocrine

Ex: histamine, cytokines, prostaglandins

through diffusion, ligands affect cells in the local vicinity

chemicals act on the cell that produced it

• secreted by neurons

  • Diffuse across the synaptic cleft and target the adjacent cell (neuron, gland, muscle)

  • Short-lived

Hormones

Neurohormones

secreted into the blood by endocrine glands to travel to distant target cells

neurons secretes hormones into the blood

• Activate or inhibit enzymes

• Direct protein synthesis through activation of transcription factors

• Stimulate cell division

• Alter membrane permeability – membrane potential or opening/closing of ion channels

• chemical substances that travel through the blood to a target cell

• Target cells must have specific receptors to which the hormone binds

• These receptors may be intracellular or located on the plasma membrane

• They trigger a change in cellular activity

Amines – amino acid derivatives

Peptides – proteins

Steroids – cholesterol based

Eicosanoids –derived from arachidonic acid (lipid)

Hydrophilic (water-soluble) hormones – dissolve in the plasma

Lipophilic (lipid-soluble) hormones – circulate bound to plasma proteins such as albumin

Lipid soluble hormones

Water soluble hormones

• Move through the plasma membrane and bind to an intracellular receptor in the nucleus

• Binding of the HRC to the DNA triggers transcription of a specific gene and the synthesis of a protein that initiates a cellular response

• utilize a membrane bound receptor

• Binding of hormone causes a conformational change in the receptor

Triggers the opening or closing of ion channels or transfers the signal to a secondary messenger within the cell which triggers a cascade of biochemical events

Ligand gated channel

Receptor enzyme

G protein coupled receptor

Integrin

Open or close the channel

Ligand binding to a receptor enzyme activates an intracellular enzyme

Ligand binding to a G protein-coupled receptor opens an ion channel or alters enzyme activity

Ligand binding to integrin receptors alters the cytoskeleton

• Amplifier enzyme activates several more molecules.

• Protein Kinase transfers phosphate from ATP to protein.

• Ca2+ binds to protein and alters the protein function.

G-protein linked receptor

G proteins

• spans the membrane and is associated with a G protein on the cytoplasmic side

  • Ligand binds to the receptor

  • Receptor then activates a G protein

relay proteins that cycle between an inactive and active form

1. G protein activates the enzyme adenylate cyclase (amplifier)

2. Converts ATP to cyclic AMP

3. Activates protein kinase A which phosphorylates other proteins

4. Trigger cellular responses

1. Binding of ligand to a G protein linked receptor or a tyrosine kinase receptor

2.  Activates phospholipase C (amplifier) which cuts PIP2(phospholipid) to DAG and IP3

3. DAG will activate protein kinase C in another signaling pathway

4. IP3 binds to calcium channels triggering the release of calcium from the SER into the cytoplasm

5. Calcium binds to and activates calmodulin (protein) which can alter other proteins to bring about a cellular response