MOLECULAR MECHANISM OF DRUG

ACTION

• Calcium &

Phosphatidyl-

inositol

• PRESENTED BY :

• SHAVYA SINGH

• M.PHARM 1ST YEAR

• (PHARMACOLOGY)

Calcium :

• Important messenger in all cells .

• Regulate diverse responses including gene

expression ,contraction, secretion, metabolism &

electrical activity.

• Calcium can enter cell through calcium channels

in plasma membrane or released by hormones or

growth factors from intracellular stores.

Types of calcium channels:

In the cell membranes their are three types of

calcium channels:

Voltage-dependent (L, N, P, Q,R, T)

Receptor operating.

Stretch activated.

Calcium channels

L-TYPE

HVA(high voltage activated)

Skeletal muscles ,smooth muscles,bone,dendrites .

P-TYPE

(HVA)

Purkinje neurons in cerebellum/cerebellar

granules cells

N-TYPE

(HVA)

Brain & peripheral nervous system

R-TYPE

Intermediate voltage activated

Cerebellar granule cells & other neurons

T-TYPE

Low voltage activated

Neurons & bones

Calcium channel blockers

• Block calcium channels (L-type) in heart and blood

vessels

• prolong depolarisation

• ↑QRS width

• block SA and AV node conduction

• heart block

• asystole

• vasodilators

• cerebral protection

Calcium channel blockers

• Hypotension

• peripheral vasodilatation and myocardial depression

• Bradycardia

• AV and SA node block

Calcium antagonists reduce coronary and

peripheral vascular resistance, decrease

blood pressure and myocardial oxygen

consumption.

Dihydro pyridines (nifedipine , amlodipine etc)

don’t have negative inotropic , chrono-

tropic and dromotropic effect in comparison to

verapamil and diltiazem, which increase

baroreflex sensibility.

Regulation of intra-cellular calcium

[Ca 2+]ext

(1000mM)

[Ca 2+]cyt

(0.1mM)

Ca 2+

ATPase

CaM

[H+]

[H+] [Na+]

[Na+]

ATPase

[K+]

[K+]

GLUCAGON

a2-ADRENERGIC

b-ADRENERGIC

VASOPRESSIN

-

[Ca 2+]m

( 0.1mM)[CaX]

( 100mmoles)

Pi

H+

[Ca 2+]er

(100mmoles)

Ca2+ATPase

REGULATION OF INTRACELLULAR CALCIUM

[Ca 2+]m [2H+]m

[2H+]c[2Na+]c

[2Na+]m

[Ca 2+]c

[Ca 2+]m

[Ca 2+]c

-180mV

DpH

0.1mM Ca2+

RUTHENIUM

RED

DILTIAZEM

MITOCHONDRIAL CALCIUM TRANSPORT

CYTOSOL

MATRIX

MATRIX CALCIUM PYRUVATE DEHYDROGENASE PHOSPHATASE

(0.8-1mM) ISOCITRATE DEHYDROGENASE

2-OXOGLUTARATE DEHYDROGENASE

PYRUVATE OXIDATION AND TCA CYCLE ACTIVITY

PYROPHOSPHATASE ACTIVITY

INCREASED PYROPHOSPHATE LEADS TO SWELLING, ACTIVATION OF

RESPIRATORY CHAIN, INCREASED ADENINE NUCLEOTIDE CONTENT AND

INCREASED ATP/ADP RATIO.

ELECTROGENICELECTRO-

NEUTRAL0.5mM

CONTROL OF CALCIUM ENTRY INTO CELLS

RYANODINE

RECEPTORS

TRP FAMILY

OF PROTEINS

(Ca2+ CHANNEL)

CIF (IP4?)

The Structure and Function of the

Calcium-Calmodulin Complex

Kinases

Phosphatases

CachannelsCa(intracellular)

Ca -calmodulin complex

Calmodulin

ATP

cAMP

MLCK*MLCK-(PO

Myosin light chain (Myosin-LC)

Myosin-LC- PO Myosin-LC

Actin

Vascular smooth muscle

Contraction Relaxation

Myosin-LC kinase (MLCK)

b agonists

Proteinkinase A

Phosphatidyl inositol

• Phosphatidyl inositol is a negatively

charged phospholipid and a minor component in the

cytosolic side of eukaryotic cell membranes.

• The inositol can be phosphorylated to form phosphatidyl

inositol phosphate (PIP), phosphatidyl inositol bi-

phosphate (PIP2) and phosphatidyl inositol tri-

phosphate (PIP3).

• PIP, PIP2 and PIP3 are collectively called

phosphoinositides.

LOCATION :

• Phosphatidylinositol is especially abundant in brain

tissue, where it can amount to 10% of the phospholipids,

but it is present in all tissues and cell types.

BIOSYNTHESIS :

• PI is formed biosynthetically from precursor cytidine

diphosphate diacylglycerol by reaction with inositol and catalysed

by the enzyme CDP-diacylglycerol inositol phosphatidyl transferase

(phosphatidyl inositol synthase )

• the other product of the reaction is cytidine mono-phosphate (CMP).

• The enzyme is located in the endoplasmic reticulum mainly,

although it may also occur in the plasma membrane in yeasts, and

almost entirely on the cytosolic side of the bilayer.

• PI is then delivered to other membranes either by vesicular transport

or via the agency of specific transfer proteins.

Types of phosphatidyl-inositol

PI-MONOPHOSPHATE

• Phosphatidylinositol 3-phosphate

• Phosphatidylinositol 4-phosphate

• Phosphatidylinositol 5-phosphate

PI-BIPHOSPHATE

• Phosphatidylinositol 3,4-bisphosphate

• Phosphatidylinositol 3,5-bisphosphate

• Phosphatidylinositol 4,5-bisphosphate

PI-TRIPHOSPHATE

• Phosphatidylinositol 3,4,5-triphosphate

Three Types of Inositol phospholipids

PI, PI(4)P, PI(4,5)P2

Phospholipase C-b

(PLC-b) Produces

DAG

(diacylglycerol) and

IP3 (inositol 1,4,5-

trisphosphate (IP3))

Gq->PLC-b

PKCACTIVE

b

g

GTP

H

PHOSPHO-

LIPASE Cb

Active

aq

P

P PIP2

P OH

PHOSPHATIDYL

INOSITOL 4,5-

BISPHOSPHATE

1,2-DIACYL

GLYCEROL

P

P IP3

P

Ca2+

ENDOPLASMIC

RETICULUM

IP3-DEPENDENT

Ca2+ CHANNEL

Ca2+

E + Cal2 + 4Ca2+ ECal2(Ca2+)4

PHYSIOLOGICAL RESPONSE

Ca2+

Ca2+

ARACHIDONIC

ACID

PHOSPHOLIPASE Cb ACTIVATION

OO P1,2-DIACYLGLYCEROL

O

O-PHOSPHATIDYLINOSITOLRAPID BREAKDOWN

FOLLWED BY RESYNTHESIS

OO P1,2-DIACYLGLYCEROL

O

O-

PHOSPHATIDYLINOSITOL-

4 PHOSPHATE

OPO32-

OO P1,2-DIACYLGLYCEROL

O

O-PHOSPHATIDYLINOSITOL-

4,5 BISPHOSPHATE1-2% OF TOTAL INOSITOL

LIPIDS

OPO32-

OPO32-

OH

OH

OHOHOH

OH

OHOHOH

OHOH

OH

SITE OF HYDROLYSIS

HYDROLYSIS OF PHOSPHATIDYL INOSITOL

4,5 BISPHOSPHATE

METABOLISM OF PHOSPHATIDYL INOSITOL

4,5 BISPHOSPHATE

OO P

O

O- OHOHOH

R1

R2OPO3

2-

OPO32-

OHOHOH

OPO32-

OPO32-

2-O3PO

OHOH

OPO32-

OPO32-

2-O3PO

OPO32-

PHOSPHOLIPASE C

PI 4,5P2

Ins (1,4,5)P3

Ins (1,3,4,5)P4

Ca2+-DEPENDENT

KINASE

R1

R2*OH

DIACYLGLYCEROL

*ARACHIDONIC

ACID

OHOHOH

OH

OPO32-

2-O3PO

Ins (1,4,)P2

OHOH

OH

OPO32-

2-O3PO

OPO32-

Ins (1,3,4)P3

PHOSPHATASE

PHOSPHATASE

PtdINS 4,5P2

(RAPID DEPLETION)

Ins 1,4,5 P3

(RAPID ACCUMULATION)

Ins 1,4 P2

(ACCUMULATION)

Ins 1 P(ACCUMULATION)

INOSITOL(SLOW ACCUMULATION)

1,2 DIACYLGLYCEROL(RAPID ACCUMULATION)

PHOSPHATIDATES(ACCUMULATES,

STIMULATED 32P

LABELLING)

PHOSPHATIDYL-CMP

Ptd INOSITOL(DEPLETED, STIMULATED32P LABELLING)

PtdINS 4,P(RAPID DEPLETION)

32P-ATP

RECEPTOR-STIMULATED BREAKDOWN

OF PHOSPHATIDYL INOSITOL 4,5 BISPHOSPHATE

STIMULUS

Ca2+ INDEPENDENTGTP

INHIBITED BY Li+

CALCIUM RELEASE BY INSOSITOL PHOSPHATES

RELEASE OF CALCIUM REQUIRES THE 4,5 PHOSPHATE

GROUPS IN THE MOLECULE

Ins1,4P2 IS INEFFECTIVE

Ins4,5P2 IS WEAK

Ins2,4,5P3 IS EFFECTIVE BUT LESS SO THAN Ins1,4,5P3

HORMONAL STIMULATION RESULTS IN THE PRODUICTION

OF TWO INOSITOL TRIS PHOSPHATES Ins1,4,5 P3 AND

Ins1,3,4 P3