cell communication

• Cell communication


  • Between cells (electrical, chemical)
  • Within cells
• Electrical transmission between cells

  1. Direct contact via gap junctions

  2. Gap junctions allow flow of current from cell-cell

  3. Rapid transmission in both directions

  4. Linked cells can act together as one unit (a 'syncytium')
• Electrical transmission between cellsexamples

  • Cardiac and some smooth muscle
• Chemical transmission between cells

  1. Cell → cell (synapse)

  2. Cell → several cells (paracrine)

  3. Many cells → many cells (endocrine)
• Chemical synapse


  • Cell → cell using chemical transmitter
  • Effect depends on transmitter and the receptor it acts on
  • One way transmission
  • Common in nervous system
• Sequence of events in chemical synapse

  1. Impulse arrives at terminal of presynaptic cell

  2. Transmitter released from storage vesicles

  3. Transmitter diffuses in synaptic cleft

  4. Transmitter binds to receptor on postsynaptic cell

  5. Alters postsynaptic cell (excitatory or inhibitory)
• Paracrine communication


  • One cell communicates with several cells locally
  • Often used by defence cells (inflammation)
  • Can be part of a 'cascade' of reactions
• Autocrine communication


  Where chemical acts on cell releasing it (feedback)
• Endocrine transmission


  • Chemical sent to all parts of the body via the blood stream
  • Hormone acts only on cells with the correct membrane receptor protein (target cells)
• Communication by nerves (neural)

  • Control of voluntary muscle contractions
  • Sensory systems
  • Salivary gland responses
  • Control of blood pressure
• Communication by hormones (humoral)

  • Gastro-intestinal gland responses
  • Control of metabolism and growth
  • Regulation of menstrual cycle
• Intracellular signalling


  • Various intracellular signalling molecules and pathways exist
  • Many act as 'second messengers'
  • 'First messenger' is the chemical transmitter which acts on a receptor protein
  • Some 'first messengers' can pass through the target cell membrane, and act on receptors inside the target cell
  • Other 'first messengers' cannot enter the cell
• Steroid transmitters


  • Steroids are lipids that can pass through the outer cell membrane
  • They act on receptors inside the target cell
  • The steroid-receptor complex acts on the DNA in the nucleus to initiate protein synthesis
  • The protein then alters cell function
  • These hormones have a delayed action
• Peptide transmitters


  • Peptide and other transmitters cannot pass through the cell membrane
  • They bind to plasma membrane receptors and set up a series of reactions controlled by 'G-proteins'
  • These in turn activate 2nd messenger systems such as: Cyclic AMP (cAMP), Calcium ions (Ca++)
• 1. protein and cyclic AMP


  1. Transmitter binds to a membrane receptor

  2. G-protein is activated by GTP

  3. ATP (in cytosol) is converted to cyclic AMP by the enzyme adenyl cyclase
• 1. protein and cyclic AMP (continued)


  1. cAMP activates an enzyme, called protein kinase

  2. This, in turn activates a specific enzyme which catalyses a chemical reaction

  3. Resulting in formation of molecule, e.g. protein
• Calcium as a 2nd messenger

  1. Transmitter binds to a membrane receptor

  2. This activates a G-protein, which activates an enzyme: phospholipase C

  3. This in turn causes opening of Ca2+ channels; Ca2+ enters by diffusion

  4. Ca2+ binds to a protein in the cytosol; here, it is calmodulin

  5. Ca2+-calmodulin complex acts as a 2nd messenger, then regulates an enzyme which regulates a chemical reaction