| Examples of intracellular receptor ligands (these cross membranes): | These ligands are cholesterol-derived hormones and include androgens (testosterone), glucocorticoids (cortisol), estrogens, mineralcorticoid (aldosterone), progesterone. An example of a non-steroid hormone example is vitamin D3. |
| Examples of intracellular receptor ligands across membranes and tend to be small, signaling molecules: | Thyroxine (T4), triiodothyronine (T3), retinoic acid |
| Examples of intracellular receptor ligands that affect ion channels: | Nucleotides, some neurotransmitters, ions |
| Examples of cell surface receptor ligands which stay in/at membrane surfaces and are stimulatory: | Polypeptide hormones mediating effects through Gs receptors: adrenocorticotropic hormone, antidiuretic hormone (ADHR vasopressin in kidney), epinephrine (ß-adrenergic) corticotrophin--releasing hormone, calcitonin, follicle--stimulating hormone, glucagon, parathyroid hormone, lutenizing hormone, thyroid-stimulating hormone, prostaglandins-activation results in increased cAMP levels. |
| Examples of ligands acting at cell surface receptors (in/at membrane locations)-these ligands mediate effects through the Gq system: | Polypeptide hormones mediating effects through the Gq system: epinephrine (alpha 1--adrenergic), angiotensin II, ADH (arterioles), thyrotropin-releasing hormone, gonadotropin-releasing hormone-The mechanism involves an increase in IP3/Calcium ions and diacylglycerol (via phospholipase C). |
| Cell surface receptor ligands (receptor system remains membrane associated)-polypeptide hormone effects mediated via Gi receptor system: | Epinephrine (alpha-2 adrenergic), somatostatin-System activation results in reduced cAMP levels. |
| Cell surface receptor ligand system that involves integral receptor tyrosine kinase enzyme activity primarily,, although some may depend on G13 receptor system: | Epidermal growth factor, insulin, insulin-like growth factor I, fibroblast growth factor, platelet-derived growth factor as well as other cytokines and growth factors.--Autophosphorylation at certain, specific receptor residues causes activation of other signaling pathways such as phospholipase C and MAP kinases. (MAP = mitogen-activated protein) |
| This receptor system depends on soluble receptor-associated tyrosine kinase, for example Janus kinase activity- some examples include: | Growth hormone, leptin, prolactin, a variety of cytokines e.g. interferon-gamma,, colony-stimulating factor. Here receptor autophosphorylation results in activation of transcription factors. |
| This receptor system depends on membrane integrated guanylyl cyclase activity: | The ligand example here is atrial natriuretic peptide, the activation of which increases cGMP through activation of guanylyl cyclase |
| Soluble receptor-associated tyrosine kinases: | Receptor tyrosine kinases, integral guanyl cyclase a.k.a. guanylyl or guanylate cyclase, Janus kinases. |
| cAMP, when acting in the role of intracellular second messenger, mediates the is hormonal responses: | Water retention by renal mechanisms through vasopressin activity, calcium regulation through parathyroid hormone activity, cardiac chronotropic (rate) and inotropic (contractile force) of heart muscle through ß-adrenergic receptor activation, making available stored energy through promoting hepatic carbohydrate catabolism and/or catabolism of fat cell triglycerides by means of ß-adrenergic receptor activation. Other regulatory sites and activities include smooth muscle relaxation, adrenal and sex steroid regulation and other endocrine and neural activities. |
| Two major functions served by second messenger reversible phosphorylation: | flexible regulation and amplification |
| Flexible regulation: | In this case the distinct specificities of protein kinases for different substrates resulting branch points in signaling pathways, thus allowing for independent regulation |
| Amplification via phosphorylation: | Phosphorylation of a serine (or threonine or tyrosine) residue is a relatively long-lasting enhancement of the regulatory activation signal. A separate enzymatic step, dephosphorylation is required to reverse the amplification step.. |
| Activity of the antibody drug: trastuzumab (Herceptin): | Growth factor receptor signaling antagonism; may be useful in breast cancer management. |
| Excitatory neurotransmitters that function by ion channel activation following their binding to a specific region in the channel protein: | Acetylcholine, glutamate; agonists include AMPA and NMDA |
| Inhibitory neurotransmitters that function by ion channel activation following their binding to a specific region in the channel protein: | Glycine or GABA (gamma-aminobutyric acid). |
| Localization sites for the nicotinic acetylcholine receptor, an example of a ligand-gated ion channel receptor: | CNS, autonomic ganglia, neuromuscular junction |
| The principal excitatory CNS transmitter: | Glutamate |
| Number of ionotropic glutamate receptors: | Three (AMPA, NMDA and kainate, which are ligands that selectively activate these types.) |