Receptors

Receptor is defined as a specific binding site with functional correlates. Receptors form the sensing elements in the system of chemical communications that coordinates that function of all the different cells in the body, the chemical messengers being hormones, transmitter substances or other mediators, such as cytokines and growth factors.

Receptors elicit many different types of cellular effects:
a)Rapid – milliseconds – synaptic transmission
b)Intermediate- seconds – action of catecholamines
c)Slow – hours/days – thyroid hormone or various steroid hormones

Many different types of linkages between the receptor occupation and the ensuing response are involved.

In terms of both molecular structure and the nature of the transduction mechanism, 4 receptor types/superfamilies are distinguished:
a)Channel linked receptors – membrane proteins. Eg. GABA nAChR receptors.
b)G protein coupled receptors – membrane proteins. Eg. mAChR Adrenoreceptors.
c)Kinase linked receptors – membrane proteins. Eg. Insulin receptors, Growth factors and cytokine receptors.
d)Receptors that regulate gene transcription – soluble cytosolic/intranuclear proteins. Eg. Steroid/Thyroid receptors.

References:
•Pharmacology by H.P.Rang, M.M.Dale and J.M.Ritter.
•Essentials of Medical Pharmacology by K.D.Tripathi