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Ca
+
Tropomyosin
alpha-1 chain
Tropomyosin
beta chain
Beta-1
adrenergic
receptor
Voltage-
depenent L-type
calcium channel
Voltage-
depenent L-type
calcium channel
Voltage-
depenent L-type
calcium channel
Ryanodine
receptor 2
cAMP-dependent
protein kinase
type I-alpha
regulatory
subunit
Sodium/calcium
exchanger 1
Voltage-gated
T-type calcium
channel (ICaT)
Voltage-gated
T-type calcium
channel (ICaT)
Sarcoplasmic/endoplasmic
reticulum
calcium ATPase
2
cAMP-dependent
protein kinase
catalytic
subunit alpha
Dobutamine
Ca
+
Ca
+
Ca
+
Na
+
Na
+
Ca
+
Ca
+
Ca
+
Dobutamine
ATP
H
2
O
Ca
+
ADP
P
i
Ca
+
Ca
+
Troponin
Troponin
G-Protein
Signaling
Cascade
Muscle
Contraction
Cardiac Myocyte
Sarcoplasmic Reticulum
High calcium binds to
troponin to displace
tropomyosin from the myosin
binding sites on the actin
filaments
Myosin and actin bind
allowing the filaments to
slide closer together,
resulting in muscle
contraction
Actin Filament
Myosin Filament
The beta-1 adrenergic
receptor is coupled to and
activates the G-protein
signalling cascade.
The G-protein signalling
cascade activates protein
kinase which activates
calcium channels on the
membrane, resulting in
calcium influx.
High calcium activates the
ryanodine receptor on the
sarcoplasmic reticulum.
Time
Membrane potential (mV)
-40mV (threshold)
Pacemaker Action Potential
Phase 0- depolarization
Phase 3- repolarization
Phase 4-spontaneous
depolarization
With acebutolol
Without acebutolol
Acebutolol, by antagonizing
beta-1 adrenergic receptors,
decreases intracellular
Ca2+. Phase 4 spontaneous
depolarization is Ca2+
dependent, therefore
acebutolol decreases the
slope of phase 4, increasing
the time it takes for
threshold to be reached and
thus slows heart rate
Cytosol
High cytosolic calcium leads
to muscle contraction
Once it reaches the heart,
it agonizes the beta-1
adrenergic receptor on the
cell membrane of myocytes.
T-tubule
Dobutamine enters the
bloodstream via intravenous
injection
Mitochondria
Calcium
TPM1
TPM2
ADRB1
CACNA1C
CACNA2D2
CACNB1
RYR2
PRKAR1A
SLC8A1
CACNA1H
CACNA1G
ATP2A2
PRKACA
Dobutamine
Calcium
Calcium
Calcium
Sodium
Sodium
Calcium
Calcium
Calcium
Dobutamine
Adenosine
triphosphate
Water
Calcium
Adenosine
diphosphate
Phosphate
Calcium
Calcium
Troponin
Troponin
G-Protein
Signaling
Cascade
Muscle
Contraction