Chapter 6


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CHAPTER 6 CELL TO CELL COMMUNICATION PDBio 362 I. Three basic methods of cell-to-cell communication: A. Direct cytoplasmic transfer of electrical and chemical signals through gap junctions B. Local chemical communication: 1. paracrines, autocrines, neuromodulators C. Long distance communication: 1. Combination of electrical and chemical signals II. Gap Junctions A. Protein channels that create cytoplasmic connections between cells (Fig. 6-1a) 1. Transfer electrical and chemical signals a) Examples: heart muscle, smooth muscle of intestine III. Chemical signals secreted by cells A. Spread by diffusion 1. limits their use to local communication B. Paracrines (Fig. 6-1 c): 1. Chemical secreted by cell that acts on other cells a) Example: histamine C. Autocrines 1. Chemical secreted by cell that acts on same cell D. Some chemical signals act as both paracrines and autocrines IV. Long-Distance Communication A. Endocrine system communicates via hormones 1. Hormones secreted into blood stream; distributed throughout circulation 2. Only react with target cells bearing receptor (Fig. 6-2) B. Nervous system 1. Electrical signals: travel through neuron to terminal where transduced into chemical signal 2. Chemical signals: secreted at neuron end; may create electrical signal in adjoining neurons a) Neurotransmitters b) Neurohormones C. Cytokines 1. Can act in both local and long distance communication 2. Paracrines or autocrines 3. Involved in cell development and immune response V. SIGNAL PATHWAYS A. Target cell receptors are found in three locations (Fig. 6-4): 1. Nucleus 2. Cytosol 3. Cell membrane B. Lipophilic signal molecules can diffuse through the phospholipid bilayer and bind to cytosolic or nuclear receptors. 1. Receptor activation usually initiates transcription of genes 2. Because of transcription, this form of communication has slow response time C. Lipophobic signal molecules are unable to enter the cell, so they bind to receptors on target cell membranes. 1. Receptor activation leads to ion movement or signal transduction/amplification pathways 2. Relatively rapid response time D. Membrane receptors and effectors can be grouped into four major categories (Fig. 6-5): 1. Ligand-gated channels 2. Receptor-enzymes 3. G protein-coupled receptors 1
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4. Integrins linked to cytoskeleton VI. Ligand-gated ion channels are the simplest receptors, A. Particularly important in nerves & muscle 1. Signal binds → Channel gate opens/closes → Ion permeability changes → Change in membrane potential → Voltage-dependent cellular response a) Example: Acetylcholine-gated cation channel of skeletal muscle VII. Receptor-Enzymes A. Receptor-enzymes: Receptors on extracellular side; enzymes on the cytoplasmic side 1. Enzymes are either protein kinases or guanylyl cyclase (GTP →GDP) (Fig. 6 10-12)
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