Cell Cell Communication and Signalling

Calcium binding calmodulin Autocrine pathway Activation of adenylate cyclase in a stimulatory G - protein pathway IP3

Cells Respond to Hormonal Signals

  1. Endodrine Signals
    1. Secreted from distant cells
    2. Long lasting in the blood stream
    3. Chemical class
      1. Amino acid derivitives
        1. thyroid
        2. adrenal medulla
        3. lipid insoluble; need receptors in cell membrane
      2. Peptides
        1. posterior pituitary
        2. lipid insoluble; need receptors in cell membrane
      3. Proteins
        1. anterior pituitary
        2. pancreas
        3. lipid insoluble; need receptors in cell membrane
      4. Steroids
        1. secreted by cells derived from mesenchymal layer during embryonic development
        2. lipid soluble
  2. Paracrine
    1. fast acting and work in immediate area (localized)
    2. Chemical class
      1. Amino acid derivitives
      2. Arachadonic acid derivitives
  3. Autocrine
    1. cells respond to their own secretions
  4. Synaptic
    1. across nerve synapses

Receptors

Lipid insoluable signals must bind to external receptor --> elicit intracellular response
  1. G - protein linked
    1. Seven pass membrane proteins
    2. Guanyl nucleotide binding protein
    3. Alpha, beta, and gamma subunits of G - protein
      1. alpha subunit is the most important because it bind to GTP
    4. Receptor --> G - protein (GDP/GTP) --> alpha subunit binds to adenylate cyclase (ATP --> CAMP)
      1. adenylate cyclase can either be inhibited or stimulated, it has two receptor sites for alpha-GTP
    5. CAMP can activate Protein Kinase A
  2. Channel linked
    1. transient opening of channel when ligand binds to the receptor
  3. Enzyme linked

Phosphatidyl Inositol Cascade

Activates phospholipase C (instead of adenylate cyclase)
  1. Cleaves PIP2: and creates two second messengers
    1. DAG and IP3: causes Ca2+ release into the cytoplasm
      1. DAG activates protein kinase C
      2. Ca2+ acts as a second messenger when cytoplasmic [Ca2+] increases
      3. Calcium binds to calcium binding proteins such as calmodulin (tissue specific binding protein)