1. Calcium as a Regulatory and
Signaling ion
Chiranjeevi Kumar
Tutor/Demonstrator
Dept of Physiology
AIIMS Bhopal

2.  Calcium facts
 Calcium history
 Plasma calcium levels
 Cellular Distribution
 Ca2+ channels
 Ca2+ binding proteins
 Role of calcium as a regulatory and signaling ion
 Calcium homeostatsis
 Research on Calcium
 Applied aspects
 Summary

3. Calcium facts
 2% of body weight
 99% in bones
 1% in body fluids
 Soft grey alkaline earth metal
 Occurs naturally in limestone, gypsum, and fluorite
 Symbol Ca & Single oxidation state +2
 Atomic Number 20 & Atomic weight 40 g/mol
 Group II element in Periodic table
 Divalent cation
 Fifth most abundant element in Earth´s crust & Essential for life.

4. Calcium history
 Latin calx or calcis meaning ”lime”
 Known as early as in first century when ancient Romans prepared lime as
calcium oxide
 Isolated in 1808 by Englishman Sir Humphrey Davy

 In 1883 Sydney Ringer demonstrated the biological significance of calcium
 Frog hearts needed the presence of calcium in the bathing solution in order
to continue beating
Sir Humphry Davy, 1st Baronet (17 December 1778 – 29 May 1829) was
a Cornish chemist and inventor. He is best remembered today for his discoveries of
several alkali and alkaline earth metals as well as contributions to the discoveries of
the elemental nature of chlorine and iodine.
He also electrolyzed a mixture of lime & mercuric acid

5. Plasma calcium levels
 In humans the concentration of calcium in the blood is – 9 - 11
mg/dL.
 Calcium in plasma or serum exists in three forms or fractions:
 1) Protein-bound calcium
 2) Ionized or free calcium
 3) Complexed or chelated calcium
Ionized or free calcium is the
physiologically active form
Complexed or chelated calcium
is bound to phosphate,
bicarbonate, sulfate, citrate,
and lactate
Protein-bound calcium cannot
diffuse through membranes
and thus is not usable by
tissues

6. Cellular Distribution
Ionic cytosol Ca is maintained at about
10-7 molar.
The differential electrical charges across
the cell plasma membrane creates an
electrical gradient that also favors Ca
entry.
Therefore, the major threat to cell
viability is excessive Ca influx from the
extracellular space along the
electrochemical gradients.
ECF Ca is 10-3 molar, the 1000-fold
chemical gradient favors Ca entry into
the cell
The defense against excess Ca influx into
cells includes

7. Ca2+ channels
 Ligand gated.
 Calcium channels opened after ligand binding to the receptor (e.g.
glutamate/NMDA receptor;ATP receptor; nicotinic ACh receptors ;
prostaglandin receptors
 Voltage gated.
 Action potental depolarizes plasma membrane, which results in the opening of
“voltage”dependent calcium channels
 Each channel protein has four homologous domains, each containing six
membrane spanning α-helices (the fourth one functions as the “voltage” sensor
 Transient.
 Long-lasting.
 Store operated calcium channels.
 Activated by emptying of intracellular stores, exact mechanism unknown

8. Type Properties Location/Function Blockers
L High activation
threshold;
slow inactivation
Plasma membrane of many
cells;
main Ca++ source for
contraction in
smooth and cardiac muscle
Dihydropyridine;
verapamil;
diltiazem
N Low activation
threshold;
slow inactivation
Main Ca++ source for
neurotransmitter
release by nerve terminals
ω-Conotoxin
(snail venom)
T Low activation
threshold;
fast inactivation
Widely distributed; important
in cardiac pacemaker and
Purkinje
cells
Mibefradil;
(verapamil;
diltiazem)

9. Ca2+ binding proteins
• Troponin.
• Calmodulin.
• Calbindin.
• Calexcitin
• Prothrombin.
• Phospholiphase A2
.
• Ca2+ ATPase.
• Calsequestrin.
• Synexin

10. Role of calcium as a regulatory and signaling ion
 Formation of bones and teeth
 As a cofactor for many enzymes and proteins
 As component in the blood clotting cascade
 In the relaxation and constriction of blood vessels
 In muscle protein degradation
 In secretion of hormones as insulin
 In nerve impulse transmission
 As a Second messenger.

11.  In Learning and memory.
 In Muscle contraction.
 In fertilization
 In immune response
 In Gene regulation
 In Cell injury
 In Modulation of ion channel activity
 In visual adaptation
Role of calcium as a regulatory and signaling ion

12. Formation of bones and teeth
Calcium is a major structural element in
bones and teeth.
Bone also acts as a store of calcium for
other body functions.
This complex provides the hard and rigid
structure of bone which is essential to its
function.
In bone calcium and phosphate combined
together in the crystalline complex;
hydroxyapatite [Ca10(PO4)6 (OH)2].
Bone is a dynamic tissue that is
'remodeled' throughout life due to
osteoclasts and osteoblasts

13. Calcium as a co-factor needed for the full activity of many enzymes, such
as nitric oxide synthase, protein phosphatases, and adenylate kinase, but calcium
activates these enzymes in allosteric regulation in a complex with calmodulin
catalyzing the production of nitric
oxide (NO) from L-arginine. NO is an
important cellular signaling molecule. It
helps modulate vascular tone, insulin
secretion, airway tone, and peristalsis
Protein kinases (PKs)
are the effectors of
phosphorylation
is a phosphotransferase enzyme that
catalyzes the interconversion of adenine
nucleotides, and plays an important role in
cellular energy homeostasis.
Calcium As A Cofactor For Many Enzymes

14. Intrinsic Pathway and
Protein Complex
Role of Calcium in Blood Coagulation

15. Extrinsic Pathway and
Protein Complex
Role of Calcium in Blood Coagulation

16. Role of Calcium in Blood Coagulation
Clotting factors (thrombin, VII, IX and X) contain a unique
modified glutamate residue, called carboxyglutamate (Gla).
This amino acid is a natural high affinity binder (or chelator)
of calcium ions, hence the designation of calcium as a co-
factor in the blood clotting cascade.
Synthesis of these Gla residues results from post-translational
modifications of the newly synthesized factors in the liver
endoplasmic reticulum by a vitamin K
Calcium - Gla-factors complex allow specific interactions
with acidic membrane lipids that ultimately lead to correct
tertiary and quaternary protein structures recognized by other
proteins in the pathway.

17. Role of calcium In the constriction and relaxation of
blood vessels

18. • Contraction in VSM can be initiated by
Passive stretching of VSM can cause contraction that originates from
the smooth muscle itself and is termed as a myogenic response
The mechanism of contraction involves different signal transduction pathways,
all of which converge to increase intracellular calcium.
chemical stimuli such as norepinephrin, vasopressin, endothelin-1,
angiotenisin 2 and thromboxane A2 can cause contraction
Electrical depolarization of the VSM cell membrane also
elicits contraction, most likely by opening voltage
dependent calcium channels (L-type calcium channels)
VSM relaxation occurs when there is reduced phosphorylation of MLC.
1) reduced release of calcium by the SR or reduced calcium entry into the cell,
2) inhibition of MLCK by increased intracellular concentration of cAMP, and
3) phosphatase-activated MLC dephosphorylation.

20. A calpain is a protein belonging to the family of calcium-dependent
nonlysosomal cysteiene proteases expressed ubiquitously in mammals
and many other organisms.
Although the physiological role of calpains is still poorly understood
but a transient and localized influx of calcium into the cell activates a
small local population of calpains close to Ca2+ channels
Calpains have been implicated
in apoptotic cell death, and appear to be
an essential component of necrosis.
Calpain
Role of calcium In muscle protein degradation
These calpains activates signal
transduction pathway and catalyzing the
controlled proteolysis of its target proteins

21. Role of Calcium In secretion of hormones as insulin

22. 22
Role Of Ca In Release Of Neurotransmitter

23. Role Of Ca In Release Of Neurotransmitter

24. Calcium influx is necessary for neurotransmitter release
and Post synaptic potentiation
Voltage-gated
calcium channels

25. Sutherland Second Messenger Hypothesis

26. First Messenger:
Neurotransmitters
(Receptor)
AGT, GnRH, GHRH
,Oxytocin, TRH
Epinephrine (α1)
Acetylcholine (M1, M3)
Signal Transducer
First Messenger:
Hormones
Primary effector Phospholipase C
GPCR/Gq
Catalyses PIP2
Secondary
effector
Second messenger
IP3; DAG; Ca2+PKC; CaM
Cellular Response
Calcium – A Versatile Second Messenger

29. Protein kinase C:
 Regulatory domain & catalytic
domain tethered together by a
hinge region
 C1 domain, present in all of the
isoforms of PKC has a binding site
for DAG
 C2 domain acts as a Ca2+ sensor
 Catalytic Region brings about
phosphorylation Ser/Thr a.a. of
proteins
 Upon activation, translocated to the
plasma membrane

30. Cell type Effects
Smooth muscle
(vascular)
Vasoconstriction
Smooth muscle
(GIT)
Contraction
Smooth muscle
(bronchi)
Bronchoconstriction
Smooth muscle
(ureter/ urinary bladder/ urethral
sphincter)
Contraction
Platelets Aggregation
Smooth muscle cells in
Ciliary muscle Contraction
Iris constrictor Constriction
Cellular responses of Protein kinase C

31. Cell type Effects
Cardiomyocytes Positive ionotropic effect
Hepatocyte Glycogenolysis,
Gluconeogenesis
Adipocyte Glycogenolysis,
Gluconeogenesis
Proximal Convoluted tubule Stimulate H+ secretion & Na+
reabsorption
Stimulate basolateral Na+-K+ ATPase
→Na+ reabsorption
neurons in CNS
neurons in autonomic ganglia
neuronal excitation
EPSP
sweat gland cells ↑secretion
ependymal cells (choroid plexus) ↑cerebrospinal fluid secretion
parietal cells ↑ gastric acid secretion

32. When calmodulin binds Ca2+, it is capable of activating five different
calmodulin-dependent kinases
One of the kinases is myosin light-chain kinase, which phosphorylates
myosin. This brings about contraction in smooth muscle
CaMKI is concerned with synaptic function
CaMKIII is concerned with protein synthesis
Another calmodulin-activated protein is calcineurin, a phosphatase that
dephosphorylates NFATC. It also plays a prominent role in activating T
cells.
Calmodulin-dependent Kinases
CaMKII is concerned with neurotransmitter secretion, transcription
factor regulation & glycogen metabolism

33. • LTP relies on calcium influx
at NMDA glutamate receptors
• Calcium channels controlled
by the NMDA receptor are
blocked by a magnesium ion
– Magnesium ion is ejected by:
1. simultaneous glutamate
binding AND
2. depolarization of the post-
synaptic cell (by activity at
AMPA receptors on the
membrane)
Role of Ca2+ in long term potentiation

34. Role of Ca2+ in long term potentiation

35. Role of Ca in Skeletal muscle contraction

36. Role of Ca in Skeletal muscle contractionRole of Ca in Skeletal muscle contraction

37. Role of Ca in Skeletal muscle contraction
Relaxation occurs when Ca 2+ is
reaccumulated in the sarcoplasmic
reticulum by the Ca 2+ ATPase of
the sarcoplasmic reticulum
membrane ( SERCA )

38. Role of Ca in Cardiac muscle contraction

39. Role of Ca in Smooth muscle contractionRole of Ca in smooth muscle contraction
Smooth muscle does not contain the
protein troponin;instead calmodulin, cal
desmon and calponin are significant
proteins expressed within smooth
muscle.
Caldesmon has been suggested to be
involved in tethering actin, myosin and
tropomyosin, and enhance the ability of
smooth muscle to maintain tension.
Calponin molecules may exist in equal
number as actin, and has been proposed
to be a load-bearing protein.

40. Role Of Calcium In Fertilization
During ovulation mammalian eggs are arrested at metaphase of their second
meiotic division and remain arrested until fertilized.
These ca2+ spikes can be termed as Ca2+ oscillations which switches on
calmodulin-dependent protein kinase II (CamKII), which phosphorylates the
egg-specific protein Emi2.
At the time of fertilisation sperm delivers phospholipase C into the egg
which triggers a series of Ca2+ spikes lasting several hours
These Ca2+ spikes are necessary for all the events of fertilization, including
exit from metaphase II arrest and extrusion of cortical granules that block
the entry of other sperm.

41. Role Of Calcium In Fertilization
To remain in metaphase II, arrested eggs must maintain high levels of
Maturation-Promoting Factor (MPF) activity, a heterodimer of CDK1
and cyclin B1.
Emi2 causes blocking of cyclin B1 results in degradation of MPF
CamKII also acts as the primary initiator in the extrusion of cortical granules.

42. Role of calcium in Immune response
TCR stimulation
[Ca++] increases
NFATc translocates to nucleus where it combines with NFATn and induces
transcription of IL-2 gene
Calcineurin: target of immunesuppressive drugs FK506 and
cyclosporine, which form a complex with immunophillins and
compete with Ca++/CaM for binding to calcineurin
dephosphorylates NFATc
Binds to Calmodulin and activates Calcineurin
T cell proliferation
no NFATc
activation

43. Role of calcium in Immune response

44. Role Of Calcium In Gene Expression
Hogan P G et al. Genes Dev. 2003;17:2205-2232
Cold Spring Harbor Laboratory Press

45. Role Of Calcium In Cell Injury
Causes of Cell Injury
Oxygen Deprivation (Anoxia)
Physical Agents
Chemical Agents
Infections Agents
Immunologic Reactions
Genetic Defects
Nutritional Imbalances
Injury mechanisms
Decreased Atp
Mitochondrial Damage
Increased Intracellular Calcium
Increased Free Radicals
Increased Cell Membrane Permeability

46. Role of calcium In Modulation of ion channel activity
• Calcium-activated potassium channels are divided into BK channels, IK
channels, and SK channels based on their conductance (big, intermediate,
and small conductance).
• This family of ion channels are activated by intracellular Ca2+.
• Calcium-activated chloride channels (CaCCs) play important roles in
cellular physiology, including
– epithelial secretion of electrolytes and water,
– sensory transduction,
– regulation of neuronal and cardiac excitability, and
– regulation of vascular tone.

47. Calcium-activated potassium channels
SK channels are activated by an increase in the concentration of intracellular calcium
through N-type calcium channels. Their activation limits the firing frequency of action
potentials and is important for regulating afterhyperpolarization in the neurons of
the central nervous system.
BK channels are essential for the regulation of contraction of smooth muscle and are
involved with the electrical tuning of hair cells in the cochlea.
IK channel is expressed mainly in peripheral tissues such as those of
the haematopoietic system, colon, placenta, lung andpancreas. The IK channel in red
blood cells was the first Ca2+–sensitive K+ channel to be identified

48. • Among all, large-conductance (BK) channels is much more sensitive to Ca2+
Each BK channel alpha subunit
consists of (from N- to C-terminal):
A voltage sensing domain (S1-S4).
A K+ channel pore domain (S5,
selectivity filter, and S6).
A cytoplasmic C-terminal domain
(CTD) consisting of a pair of RCK
(Regulator of Conductance of K+)
domains
Second RCK domain. contains four
primary binding sites for Ca2+, called
"calcium bowls"
Role of calcium In Modulation of ion channel activity

49. Phototransduction
•Starts with photon absorption by
rhodopsin
•Transducin binds to activated
rhodopsin , exchanges GTP for GDP
•Activated transducin dissociates into
 and  subunits
•The  subunit binds to, and
activates, phosphodiesterase
•Intracellular cGMP concentration
decreases
•Reduction in cGMP closes cGMP-
gated cation channels in the plasma
membrane
•Membrane potential hyperpolarizes
•Closing of cGMP-gated channel
reduces intracellular calcium
•Reduced calcium counteracts the
effects of light absorption
Role of Ca2+ in visual adaptation

50. Role of Ca2+ in visual adaptation

51. Calcium homeostatsis

52. Exercise and Calcium
• Normal bone function requires weight-bearing exercise
• Regular physical activity has been associated with many positive
health benefits including strong bones.
• Proper calcium consumption & adequate weight-bearing
physical activity early in life is important in reaching peak bone
mass.
• Weight-bearing physical activities cause muscles and bones to
work against gravity
• Lack of weight-bearing exercise decreases bone formation
• Total bed-rest causes bone loss and negative calcium balance

53. Research on Calcium
See in particular:
• Calvo MS et al., “overall trend in food consumption in the US is to drink
less milk and more carbonated soft drinks.” Nutrition 2000 Vol 16 (7/8).
• Calvo MS et al., “ High sodium associated with fast-food consumption
competes for renal reabsorption of calcium and PTH secretion “
• Harland BF et al., “ Caffeine induced calcium loss “. Nutrition 2000 Vol
16 (7/8)
• Intake of carbonated beverages (soda pop) has been associated with
increased excretion and loss of calcium
• Excessive intake of Na may cause renal hypercalciuria by impairing Ca
reabsorption

54. Applied aspects
Hypocalcemia
Hypercalcemia
Lambert – Eaton syndrome
COFFIN – LOWRY syndrome (RPS6kA3)
Timothy's syndrome (Long QT syndrome) (LTQ1 – 13)
WOLFRAM syndrome (DIDMOAD)

55. Toxicology
• The UL for calcium is 1200 - 1500 mg/day
• MAS (Milk alkali syndrome)
- Rare and potentially life threatening condition in individuals
consuming large quantities of calcium and alkali
- Characterized by renal impairment, alkalosis and
hypercalcemia: cause progressive depression of the nervous
system

56. Final word
•Calcium
A “vital life element”
not to be ignored
A very exciting area
for research

57. Thank you for your attention

58. • Rolein surfactant
• Role in peripheral chemoreceptors in chemical
regulation of respiration