What are the mechanisms by which cells send and receive signals?

1. What are the mechanisms by which cells send and receive signals?

2. Cell to Cell Communication Fig. 1-34 Ganong • via direct contact • surface contact • gap junctions • indirect contact via chemical messengers • synaptic transmission • autacoid (paracrine/autocrine) transmission • endocrine transmission

3. Surface Contacts • important in the regulation of cell behavior • examples • antigen presentation • contact inhibition of movement • contact inhibition of growth • mechanisms beyond the scope of this course

4. cardiac myocyte Fawcett , Histology Gap Junctions gap junction • gap junction / nexus • direct connection between the cytosol of two cells via connexons (transmembrane channels) • Connexons allow small substances (ions, small molecules) to pass between cells. • electrical coupling • e.g., between cardiac and visceral smooth muscle cells • chemical coupling • e.g., between liver cells cytosol: cell A intercellular space cytosol: cell B Fig. 5.28 cytosol: cell A Fig. 1-13 Ganong cytosol cell B

5. Synaptic Transmission Fig. 1-34 Ganong • synapse: a junction between two excitable cells • chemical synapse: typical synapse (cf. electrical synapse: gap junction) • electrical signal (sending cell)  chemical signal (from sending to receiving cell via synaptic cleft)  electrical signal (receiving cell) • precise delivery of chemical signal due to synaptic anatomy • rapid delivery of signal (msecs) • brief response by receiving cell

6. Fig. 1-34 Ganong Paracrine Transmission • sending cell  extracellular fluid  receiving cell • e.g., mast cell release of histamine • localized response • less precise and less rapid delivery than synaptic transmission • autocrine transmission: The receiving cell is the same as the sending cell. • Chemical signals that typically work via paracrine and autocrine transmission (e.g. cytokines, prostaglandins, histamine) are called autacoids. • The term autacoids distinguishes these agents from endocrine signals, known as hormones.

7. Endocrine Transmission Fig. 1-34 Ganong • chemical signal (hormone) transmitted to target cells via the blood • sending cell  extracellular fluid  blood  extracellular fluid  receiving cells (target cells) • no anatomical precision • precision due to specificity of receptors on target cells • slow delivery and slow response • most hormones: seconds to minutes • steroid and thyroid hormones: response time in hours to days

8. Cellular Receptors for Chemical Signals Fig. 1-34 Ganong • In cell to cell communication via chemical signals, specificity depends on receptors. - Target cells have receptors that are specific for the chemical signal.

9. Receptors(of chemical signals) • The binding of the ligand to the receptor is specific. • One ligand can have different effects on different tissues due to • different receptor types • different intracellular mechanisms nicotinic cholinergic receptor muscarinic cholinergic receptor Fig. 15-9, Alberts et al., Molecular Biology of the Cell

10. Receptors(of chemical signals) (including prostaglandins, see Fig. 17.26) • Receptor location varies • cell surface • intracellular • cytosol • nucleus e.g., steroid and thyroid hormones Fig. 17.20

11. Receptor TheoryIntracellular Receptors • Intracellular receptors work by altering gene expression. • e.g., thyroxine • slow response • hours to days Fig. 17.21

12. Receptor TheoryCell Surface Receptors • Cell surface receptors (transmembrane proteins) • channel-linked receptors (ligand-gated channels) • non channel-linked receptors • G-protein systems • enzyme-linked receptors Fig. 15-15, Alberts et al., Molecular Biology of the Cell