Calcium channels play a key role in many cellular functions by regulating intracellular calcium levels. There are several types of calcium channels that influence calcium influx and release from intracellular stores. Voltage-dependent calcium channels include L-type, N-type, P/Q-type, R-type, and T-type channels that are involved in processes like muscle contraction, neurotransmitter release, and pacemaking. Dysfunctions in calcium channels can lead to channelopathies like hypokalemic periodic paralysis or malignant hyperthermia. Calcium channels are also important therapeutic targets, with calcium channel blockers and other drugs influencing channels to treat conditions like hypertension, angina, epilepsy, and migraines.
2. • Function.
• Types of Calcium channels.
• Channelopathies.
• Therapeutics Uses of Calcium .
3. Function
• Signal transduction pathways, second messenger
• Neurotransmitter release from neurons
• Contraction of all muscle cell types
• Many enzymes require calcium ions as a cofactor (blood-clotting
cascade)
• Extracellular calcium is also important for maintaining the potential
difference across excitable cell membranes, as well as proper bone
formation.
•
5. Ventricular AP Function
• Phase 4: resting membrane
potential near the K+
equilibrium potential.
• Phase 0: depolarizing impulse
activates fast Na+
channels
and inactivates K+
channels.
• Phase 1: Transient opening of
K+
channels and Na+
channels
begin to close.
• Phase 2: Ca2+
channels are
open, key difference between
nerve AP.
• Phase 3: repolarization, Ca2+
inactivate and K+
channels
open.
• Refractory period: Na+
channels are inactive until
membrane is repolarized.
6. FUNCTION
The synthesis and release of
insulin is modulated by:
1. Glucose (most
important), AAs, FAs
and ketone bodies
stimulate release.
2. Glucagon and
somatostation inhibit
relases
3. α-Adrenergic
stimulation inhibits
release (most
important).
4. β-Adrenergic
stimulation promotes
release.
5. Elevated intracellular
Ca2+
promotes release.
Example of how an endocrine cell
(pancreatic β-cell) depolarizes its
membrane with Ca2+
to release
insulin.
7. Classes of Ca+2
channels
– Voltage- Sensitive (VDCCs)
– Receptor- Operated (Ligand- Gated ion channels)
– Leakey channels
8.
9. VDCCs
• The possible existence of VDCCs was first reported by
Hagiwara in 1975 using egg cell membrane of a starfish.
• They were initially divided into 2 classes HVA & LVA ca+2
channels.
• HVA ca+2
channels are further divided into L,N,P/Q & R-types
channels,
• LVA ca+2
channels consists of only T-type channels.
• R-type is occasionally classified as ( IV A ) channels.
10. Structure & Function
L-TYPE Ca+2
CHANNEL
• It is composed of 5 different polypeptide subunits, different mol
masses
ι. α1(175KD) , which forms the ion channel & contains ca+2
antagonist binding sites.
ιι. α2(143KD), which is associated with α1 & does not contain any
high-affinity binding site.
ιιι.β(54KD),
ιϖ.γ(30KD),
ϖ. δ(27KD).
12. N-TYPE Ca+2
CHANNEL
• It is purified from the rat brain.
• It is composed of 4 subunits:
∀ α1 , α2 , γ , & β.
• role -- neurotransmitter release.
13. P/Q-TYPE Ca+2
CHANNEL
• It is composed of α1, α2, δ & β subunits.
• Play similar role - N-type calcium channel (NT release at e presynaptic
terminal & neuronal integration in many neuronal types.
• They are also found in Purkinje fibers in the electrical conduction system of
the heart.
• P channels were discovered in cerebellar Purkinje cells by Llinas and
Sugimo
14. T-TYPE Ca+2
CHANNEL
• T-type VDCCs are activated at negative membrane potentials
close to the resting potential.
• the T-type channel is thought to be responsible for neuronal
oscillatory activity, which is proposed to be involved in process
such as sleep / wakefulness regulation & motor coordination.
• In addition ,T-type ca+2
channels are involved in pacemaker
activity.
16. Receptor – Operated Channels
( Ligand – Gated Ion Channels)
• Independent of membrane depolarization
• It is found on the plasma membrane
• composed of 4 or 5 subunits in various combinations depending
on the particular receptor.
17. LIGAND – GATED ION CHANNELS
Type Gated by Genes Location Function
IP3 receptor IP3
ITPR1,
ITPR2,
ITPR3 ER/SR
Releases
calcium from
ER/SR in
response to
IP3 by
Ryanodine
receptor
Dihydropyridi
ne receptors
in T-tubules
and
increased
intracellular
calcium
(CICR)
RYR1,
RYR2,
RYR3
ER/SR Calcium-
induced
calcium
release in
myocytes
Cation
channels of
sperm
store-
operated
channels
indirectly by
ER/SR
depletion of
calcium
ORAI1,
ORAI2,
ORAI3
plasma
membrane
18. LEAKEY Ca+2
CHANNELS
• small amount of Ca+2 leak into resting cell and pump out by
Ca+2 ATPase
• Mechanical stretch promotes inward movement in Ca+2
occurring through activation of leaky channels or separate
stretch sensitive channels.
21. CHANNELOPATHIES
HYPOKALEMIC PERIODIC PARALYSIS
Prevelance 1:100,000
Symptoms during attacks Acute onselt flaccid paralysis
Proximal >>> distal
Triggers High carbohydrate,
High salt,
Drugs- beta agonists,
Insulin
Rest following prolonged exercise
22. CHANNELOPATHIES
Malignant hyperthermia
• Mutation of the ryanodine receptor (type 1), located on the
sarcoplasmic reticulum , that stores calcium.
• RYR1 opens in response to increases in intracellular Ca2+
level
mediated by L-type
• RYR1 has two sites for reacting to changing Ca2+
concentrations; A-
site and the I-site.
23. Malignant hyperthermia
Skeletal muscle Rigidity and weakness
Rhabdomyolysis
Muscle spasms especially
affecting Masseter, but can
be generalised
myalgia
Autonomic Sympathetic overactivity
Hyperventilation
Tachycardia
Haemodynamic instability
Cardiac arrhythmia
Laboratory Increased oxygen consumption
Hypercapnia
Lactic acidosis
Raised creatine kinase
Hyperkalaemia
24. Malignant hyperthermia
Triggers Full episodes: general anaesthesia (inhalational
agents— isoflurane, desflurane,) suxamethonium
Milder malignant hyperthermia: exercise in hot
conditions, neuroleptic drugs, alcohol, infections
Treatment Dantrolene 2 mg/kg intravenously every 5 minutes to
a total of 10 mg/kg
Avoid calcium, calcium antagonists, b-blockers
25. Timothy syndrome
• AD.
• classical (type-1) and atypical (type-2).
• Physical malformations, as well as neurological and developmental
defects.
• They are both caused by mutations in CACNA1C, the gene
encoding the Ca2+
α subunit.
• Mutations in CACNA1C cause delayed channel closing & thus
increased cellular excitability.
26. THERAPEUTICS USES OF Ca+2
CHANNELS
• Calcium channel blockers (CCBS).
• Calcium Channels role in Anesthetics.
• Antiepileptic
• Prophylaxis of Migraine.
• Rx of infestation.
• Other roles
28. CCBS MECHANISM OF ACTION
• block calcium entry into cardiac and vascular smooth muscle at
the alph1 subunit of the L-type voltage-gated calcium ion
channels (slow channels)
• Increase the time that Ca 2+
channels are closed
30. MECHANISM OF ACTION
• volatile inhalational anesthetics at clinically relevant conces. inhibit
inward currents through VDCCs in a dose-dependent manner
without an apparent change in the time course of activation or
inactivation.
• The I.V anesthetics thiopental, ketamine & propofol all inhibited
inward ca+2 currents through L- type VDCCs of porcine tracheal
smooth muscle cells
31. USES OF Ca+2
CHANNELS
Local anesthetics
Mechanism
• Lidocaine at clinically relevant conces. has been shown to inhibit
inward ca+2
currents in ganglionic neurons & in frog dorsal root
ganglionic cells.
• Lidocaine, tetracaine & bupivacaine also inhibit the VDCC activity of
cardiac myocytes in the chick, guinea pig & hamster, respectively.
32. USES OF Ca+2
CHANNELS
As Antiepileptic ..
Valproic acid (Na valproate) Ethosuximide
Absence seizures, GTCS, CPS
Juvenile myoclonic epilepsy,
Lennox-Gastaut syndrome,
second-line treatment of status
epilepticus,
post-traumatic epilepsy.
(neurodegenerative diseases such as
Alzheimer's disease and Huntington's
disease)
Absence seizures
Anorexia, vomiting drowsiness, ataxia Hypersensitivity rashes, blood
dyscrasias.
•Blocks voltage-gated sodium channels
& T-type calcium channels.
•Affect the function of the
neurotransmitter GABA
•Inhibitor of the enzyme histone
deacetylase 1
Reduced low-threshold Ca2+
currents in
T-type Ca2+
channels in thalamic neuron
33. USES OF Ca+2
CHANNELS
Prophylaxis of Migraine.
Flunarizine.
• non-selective calcium entry blocker + histamine H1 blocking
activity.
• Also Na channel blocker
SE;
Sedation, constipation, dry mouth, wt gain, extrapyramidal
effects, drowsiness.
34. USES OF Ca+2
CHANNELS
Infestation treatment
• Praziquantel
– Rx Tape worms, flukes worms.
Mechanism --increases the permeability of the membranes of cells
towards calcium.
SE-
• dizziness, headache, and malaise, drowsiness, somnolence,
fatigue, and vertigo.
• Urticaria, rash, pruritus
35. Summary
• Intracellular free ca+2
is important for regulation of cell function.
• Increase in concen. of intracellular free ca+2
can be obtained by
rapid but transient ca+2
release from intracellular ca+2
stores & by
slow ca+2
influx from the extracellular space.
• VDCCS serve as one of the important mechanisms for ca+2
influx
into the cells, enabling the regulation of intracellular free ca+2
concentration.
36. Summary
L N P/Q R T
VA HVA HVA HVA IVA LVA
location heart Neuronal Neuronal Neuronal Heart
function Contraction Release Release Release Pacemaker
An increase in intracellular calcium activates myosin light-chain kinase, resulting in phosphorylation of myosin light chain, actin-myosin interactions, and smooth muscle contraction
Insulin secretion - Insulin secretion in beta cells is triggered by rising blood glucose levels. Starting glucose by the GLUT2, t glycolytic phosphorylation of glucose COZ a rise in the ATP:ADP ratio. rise inactivates Kchannel Dat depolarizes membrane, COZ calcium channel 2 open up allowing calcium ions to flow inward. rise in levels of calcium leads to the exocytotic release of insulin from their storage granule.
The ca +2 channel can be divided into subtypes according to their electrophysiological characteristics & each subtype is encoded by its own gene
"L" stands for long-lasting referring to the length of activation P-type ('P' for cerebellar Purkinje cells) N-type ('N' for "Neural-Type" ) calcium channels are found primarily at presynaptic terminals , are involved in NT release "T" stands for transient referring to the length of activation.
low-voltage-activated (LVA) channels-activated by small depolarizations of the PM found in excitable cells ( e.g. , muscle, glial cells, neurons, etc.) high-voltage-gated calcium channels (HVGCCs). High-voltage-gated calcium channels include the neural N-type channel blocked by ω-conotoxin GVIA, R-type channel (R stands for R esistant to the other blockers and toxins, except SNX-482) involved in poorly defined processes in the brain, closely related P/Q-type channel blocked by ω-agatoxins, dihydropyridine-sensitive L-type channels responsible for excitation-contraction coupling of skeletal, smooth and cardiac muscle and for hormone secretion in endocrine cells
It is high conce. in skeletal muscle. L-type VDCCs are expressed ubiquitously in neuronal, endocrine, cardiac, smooth, & skeletal muscle, as well as in fibroblasts & kidney cells the generation of AP & to signal transduction at cell membrane L-type VDCCs in the process of neurotransmitter secretion of the central nervous system
L-type ca +2 channels are linked to ryanodine receptor of sarcoplasmic reticulum. Abnormal ryanodine receptor causes malignant hyperthermia a hypermetabolic crisis triggered by suxamethonium & volatile anesthetics.
Strong depolarization by an AP COZ channels to open & allow influx of Ca 2+ , initiating vesicle fusion & release of stored neurotransmitter. channels blocked by ω-conotoxin
Immunohistological studies Channel is widely expressed --mammalian central nervous system neuronal integration-- process by wic inhibitory & excitatory postsynaptic potentials summate & control the rate of firing of a neuron.
main subunit 1 can function as ca +2 channel. Other subunits ( 2 / & ) contribute to the regulation of a ca +2 channel function by changing drug affinity & / or voltage dependence.
the receptor-operated calcium channels (in vasoconstriction) Binding adr or others
Calcium Induced Calcium Release - (CICR) The cation channels of sperm AKA Catsper channels or CatSper , are ion channels that are related to the two-pore channels and distantly related to TRP channels. The four members of this family form voltage-gated Ca 2+ channels that seem to be specific to sperm. These channels are required for proper fertilization.The study of these channels has been slow because they do not traffic to the cell membrane in many heterologous systems. Transient receptor potential channel
mutation slows the activation rate of L-type Ca current to 30% of Normal. voltage-sensitive sodium channel gene ( SCN4A ). voltage-sensitive, skeletal muscle calcium channel gene, CALCL1A3
FIRST AND SECOND DECADE OF LIFE
A-site (high affinity Ca 2+ binding site) mediates RYR1 opening. I-site(lower affinity site ) mediates the protein's closing Caffeine, halothane, act by increasing the affinity of the A-site for Ca 2+ & decreasing t affinity of I-site in mutant proteins Ca 2+ consumes large amounts of ATP, generates the excessive heat (hyperthermia). muscle cell is damaged by the depletion of ATP , possibly high temp
QT-prolongation, heart arrhythmias, structural heart defects, syndactyly and autism spectrum disorders. Early childhood death. Calcium channel, voltage-dependent, L type, alpha 1C subunit (also known as Ca v 1.2 ) (webbing of fingers and toes) QT interval represents electrical depolarization and repolarization of the left and right ventricles. A lengthened QT interval is a biomarker for ventricular tachyarrhythmias like torsades de pointes &a risk factor for sudden death.
The effects of various kinds of anesthetics in a variety of cell types have been demonstrated & a number of clinical effects of anesthetics can be explained by their effects on ca +2 channels.
Effect of these anesthetics that can account for their airway smooth muscle relaxant effects. Ikemoto first demonstrated in 1985---halothane decreased inward ca +2 slow currents in ventricular myocytes in rats Terrar reported the inhibitory effect of halothane & isoflurane on ca +2 channels of cardiac myocytes from the guinea pig ventricle.
JME 12-18 idiopathic generalized epilepsy + myoclonus occurring early in the morning LGS 2-6 TH YEAR Difficult-to-treat form of childhood-onset epilepsy + characterized frequent seizures & different seizure types + developmental delay and psychological & behavioral problems.
decrease intracellular ca release Cerbro selective ca channel blockers USES; occlusive peripheral vascular disease, vertigo of central & peripheral origin. reduce headache frequency and severity in both adults & children .
ions,induces contraction, resulting in paralysis in the contracted state. The dying parasites are dislodged from their site of action in the host organism and may enter systemic circulation or may be destroyed by host immune reaction