Cell Communication & Receptor Families

Cell Communication

Cell Communication Importance

• Essential for body function, environmental sensing, and response.
• Understanding it is crucial because:
  • Disorders can lead to diseases (e.g., nervous and endocrine system).
  • Most drugs act by modifying cell-to-cell communication.

Types of Cell Signaling

• Local Signaling:
  • Paracrine: signaling molecule acts on nearby cells (e.g., immune responses).
  • Synaptic: communication between neurons (e.g., thoughts and memories).
• Long Distance Signaling:
  • Endocrine: hormone released into bloodstream, travels to target cell (e.g., insulin).

Cell Signaling Stages

1. Reception: signaling molecule binds to receptor.
2. Transduction: signaling pathway initiated.
3. Response: cellular response activated (e.g., enzyme activation).

Receptors

• Proteins that bind to signaling molecules (ligands/agonists) to elicit a response.
• Hydrophilic molecule receptors are on the cell surface.
• Hydrophobic molecule receptors are intracellular.
• Transduction pathway and response depend on receptor type and cell type.

Receptor Families

1. Ligand-gated ion channels
2. G protein-coupled receptors
3. Tyrosine kinase receptors
4. Steroid receptors

Neurotransmission Receptors

1. Ligand-gated ion channels:
   • Fast, direct neurotransmission.
   • Ions flow into/out of cell, changing membrane voltage (IPSPs and EPSPs).
2. G protein-coupled receptors:
   • Slower, indirect neurotransmission.
   • Activation modifies depolarization or hyperpolarization.

G Protein-Coupled Receptors

• Large family; many drug targets.
• Activation causes a cascade of effects.
• Phosphorylation (addition of phosphate groups by kinases) controls protein activity.
• Dephosphorylation (removal of phosphate groups by phosphatases) also controls protein activity.
• Amplification enables pronounced cellular response from low neurotransmitter concentrations.

Neurotransmitters

• Effect depends on receptors expressed by the postsynaptic cell.

Tyrosine Kinase Receptors

• Membrane receptors responding to hormones.
• Important for metabolism and growth.
• Receptor dimerization leads to autophosphorylation and activation of other proteins.
• Often involves phosphorylation cascades leading to gene transcription.

Steroid Receptors

• Intracellular receptors for lipophilic hormones.
• Translocation to nucleus, triggers gene transcription (slow process).