receptors families

Receptor families:
1- ligand gate ion channel:
Regulate the flow Of ions Across cell membrane , the ligand has binding site
( receptor) on channels , very rapid time scale is millisecond.
Eg/Ach bind to nicotinic receptor and increase Na+ influx leading to depolarization and sk. M

Diazepam increase Cl- influx producing hyperpolarization.

2- G-protein coupled R
The ligand bind to receptor , conformational changes occur that lead to activation of G- pr. in cell mem (consist of ? subunit( the large subunit bind with GDP) , ? and ? ) the ? subunit will separate from other and GDP convert to GTP that activate enzymes in cell mem
1- adenylyl cyclase cAMP (second messenger)
2- guanylyl cyclase cGMP ( in intestinal mucosa and vascular sm)
They regulate protein phosphorylation)
3- phospholipase C IP3 and DAG they regulate intracellular Ca++

Eg/ Neurotransmitter (As epinephrine )
Histamine
Serotonin
Ach on muscarinic R
Time scale seconds – miniutes

3- Enzyme linked R
Have cytosolic enzyme activity after auto-phosphorylation
Eg/ insulin , epidermal growth factor, platelet derived growth factor
Time scale minutes – hours

D+R=conformational changes active kinase autophosphorylation
Phosphorylate tyrosin on specific pr activate other cellular effect

4- intracellular Pr.
The ligand must be lipophilic so can diffuse through cell mem and bind to intracellular R forming ligand-R complex by specific factor the complex transported into nucleus regulating gene expression and synthesis of new pr

Time scale: hours

Drug combination:
1- synergistic 1+1=4
2-potentiation 0+2=3
3-addative 1+1=2
4- antagonist 1-1=0