MOLECULAR MECHANISM OF DRUG ACTION

CELLULAR SIGNALLING

What is cell signalling Cell signalling within, between & among the cell & their classification

A. EXTRACELLULAR- protein, peptides, AA, hormones, PG, Steroids, etc 1) Intracrine – signal produced & stayed in target cell itself

2) Autocrine – target cell, are secreted and effects on target cell via receptor

3) Paracrine - target cell in viscinity,,,eg NeurotransmitterLocal chemical mediators- GF, PG

4) Endocrine- duct, hormone,distant cell-- insulin, thyroxine, adrenaline

5) Juxtracrine- signal targets adjascent cell

6) Gaseous- NO, CO 7) Neuronal- synapses

B. INTRACELLULAR

• Ca2+ : ions• DG, ceramide : lipid derivatives• IP3 : carbohydrate derivatives• cAMP cGMP : nucleotides• Ras, JAK, Raf : proteins

SECOND MESSENGER Ca2+,DAG, Ceramide, IP3, cAMP, cGMP

THIRD MESSENGER- transmit signal from outside to inside or inside to outside of nucleus/ DNA binding protein

MOLECULAR MECHANISM OF DRUG ACTION

RECEPTOR OCCUPANCY :- The receptor concept Nature of drug receptor interaction 1.Receptor occupancy model-

Law of mass action More receptor occupied more effect at equilibrium

2.two state receptor model- inactive and active 3.ternary complex model- ligand,receptors and G-protein 4. competitive inhibitory model.

TRANSDUCER MECHANISM

What are receptors ? Able to recognize and bind to corresponding ligand molecules, become

activated, and transduce signal to next signaling molecules.

Glycoprotein / lippoprotein 1. G-Protein coupled receptors 2. ligand gated Ion channel receptors 3. Enzyme linked receptor 4. Nuclear/Steroidal receptor

LIGAND GATED ION CHANNEL RECEPTORS

LIGAND GATED ION CHANNEL RECEPTORS

Nicotinic acetylcholine receptor NMDA- type glutamate receptor Glycine receptor GABAA receptor Serotonin receptor (5-HT3)

NMDA- type glutamate receptors

ENZYME LINKED RECEPTORS

1. Intrinsic tyrosine kinase receptors

2. JAK-STAT kinase binding receptors

NUCLEAR RECEPTORS

SteroidsHormonesPituetory hormones

CYCLIC NUCLEOTIDES

cAMP - 3’5’-cyclic adenosine monophosphate, cGMP- 3’5’-cyclic guanosine monophosphate, cCMP- cytidine 3',5'-monophosphate, and cUMP- uridine 2',3'-cyclic phosphate.

cyclic nucleotide Known binding proteins Pathway/Biological association

cAMP

1.protein kinase A2.cyclic nucleotide-gated ion channels3.Epac4.Catabolite Activator Protein (CAP)

1.smooth muscle relaxation[14]

2.photo/olfactory receptors[3]

3.glucagon production in pancreatic beta cells[15]

4.lac operon regulation in E. coli[16][17]

cGMP

1.cGMP-dependent protein kinase

 (PKG)2.cyclic nucleotide-gated ion channels

1.smooth muscle relaxation[14]

2.photo/olfactory receptors[3]

cCMP 1.cGMP kinase I2.protein kinase A

1.smooth muscle relaxation[12]

[18]

CYCLIC NUCLEOTIDE PATHWAYS

CALCIUM

Calcium- major intracellular cationCalcium – heart (ion channel)As second messenger

Role of Calcium at –

Skeletal Muscleneurone

MECHANISM OF ACTION

IP3 AND DAG

IP3-DAG PATHWAY

ION CHANNELS AND THEIR MODULATORS

Sodium Calcium Potassium Types – voltage gated or ligand gated

Modulators-

1. SODIUM ION- a) Voltage Gated b) Ligand gated - Role in Action potential

SODIUM CHANNELS

Structure-

DIVERSITY-

Subunits- a) alpha subunit b) Beta subunit

Sr.no

Protein name

gene Expression profile associated

1 Nav 1.1 SCN 1A Central & peripheral neuron, myocytes

Febrile epilepsy

2 Nav 1.1 SCN 2A -’’- Inherited seizures

3 Nav 1.3 SCN 3A -”- ------

4 Nav 1.4 SCN 4A -”- Paralysis,myotonia

5 Nav 1.5 SCN 5A Cardiac myocytes, central neuron

Long QT syndromes

Sr.no Protein name

gene Expression profile

Associated

6 Nav 1.6 SCN 8A Skeletal muscle Epilepsy

7 Nav 1.7 SCN 9A DRG Fibromyalgia

8 Nav 1.8 SCN 10A DRG ------------

9 Nav 1.9 SCN 11A DRG -------------

10 Nax SCN 7A Heart,uterus,SM ----------------

β-subunitNav β1-- Nav β4

PHARMACOLOGICAL MODULATION

Activators-AconitineBatracotoxinBrevetoxinCiguatoxinVeratridine

Gating modifiers-Peptide based toxin-µ-conotoxinΔ-atracotoxinScorpian venum

Blocker-Class-1A- Quinidine, procainamideB- LidocaineC- propafenone

CALCIUM CHANNEL

Structure

VOLTAGE GATED CALCIUM CHANNEL

type voltage Αlpha 1-subunit

Genes occurance

L-type High volt. Activated(HVA)

α2, δ,β,γ Cav 1.1-1.4

SM, dendrites & spines

P-typeOrQ-type

HVA α2, δ,β Cav2.1 Purkinje neurones,cerebellar granules

N-type HVA α2, δ/β, β3,β4

Cav2.2 Trough out brain

R-type Intermidiate voltage

α2, δ,β Cav2.3 Cerebellar granule cells

T-type Low voltage ----------- Cav3.1-3.3 Bones, neuronal cell having pacemaker activity

Sr no.

type Gated by gene location Function

1 IP3 IP3 ITPR1-3 ER/SR Release ca+

2 Rynodine receptor

DHPR,in T-tubule

RyR1-3 ER/SR Release in myocytes

3 Two pore channel

------- ---------------------

------------- -------

4 Store operated

Indirectly by ER/SR depletion of ca+

ORAI1-3 Plasma membrane

--------

LIGAND GATED CALCIUM CHANNEL

PHARMACOLOGY OF CALCIUM CHANNEL

Calcium channel blockers-1. L-type- DHPD, phenylalkylamines, benzothiazepines.2. P/Q – type- ω-Agatotoxin 3. N- type- ω-conotoxin4. R-type-SNX 4825. t-type- ethosuccimide

Activators– GPCR , Calcium etc.(may be)

POTASSIUM CHANNEL

Structure and types:-

a.2T1P, b.6T1P, c.8T2P, d.4T2P

K CHANNEL

K CHANNEL

class subclass function blocker ActivatorsCa+ Activated 6T&1P

BK

Sk

Decrease then increase intracellular calciumCellular calcium

Charybdotoxin

apamin

1-EBIONS309

CYPPA

Inwardly rectifying2T&1P

ROMK

GPCR regulated KirATP sensing

Recification& secretion of KMediate or inhibit effects of GPCRClose when high ATP

--

Ifenprodil

Tolbutamide etc

----

GPCR agonist

pinacidil

Tandem pre domain4T&2P

TWICKTREKTASKTALK 1&2THICK & TESK

Resting mem. Pot. bupivacaine Halothane

Voltage gated 6T&2P

hERG(Kv11.1)

Kv LQT(7.1)

Repolarisation

Limits freq. of AP

Tetraethyl ammonium4-aminopyridine

Ritagabine

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