Cardiac action potential and
underlying ionic currents:
methods, physiology and selected pathologies
Assoc. Prof. MUDr. Markéta Bébarová, Ph.D.
Department of Physiology
Faculty of Medicine
Masaryk University
Selected Lessons from Physiology
Assoc. Prof. MUDr. Milena Šimurdová, CSc.
Assoc. Prof. RNDr., Ing. Jiří Šimurda, CSc.
Ganong´s Review of Medical Physiology, 23rd edition
http://tmedweb.tulane.edu/tmedwiki/doku.php/intro_to_the_h
eart_cardiac_electrophysiology
http://tmedweb.tulane.edu/tmedwiki/doku.php/intro_to_the_heart_cardiac_electrophysiolo
gy
Ionic Base of Action Potential
Ionic Channels
Ganong´s Review of Medical Physiology, 23rd edition
Impact of Knowledge on Electrical Properties
of Cardiac Cells for Clinical Medicine
 Inherited Arrhythmogenic Syndromes
 Acquired Arrhythmogenic Syndromes
- on a base of other primary cardiac diseases
- side effects of drugs
- effects of other substances including addictive drugs
 Sudden Cardiac Death
 Mechanisms of Action of Antiarrhythmic Drugs
1) Whole organism (ECG)
3) Multicellular cardiac samples
Electrophysiological Methods
in Cardiology
Zipes D. a Jalife J. (2003)
Cardiac Electrophysiology: From Cell To Bedside
5) Single membrane channels
4) Isolated cardiomyocytes
2) Isolated heart (Langendorff)
potential difference φ between two points
of a volume conductor
(outside the cells)
V = φ2 - φ1
1) Whole organism (ECG)
2) Isolated heart (Langendorff)
measured quantity: voltage (V)
Electrophysiological Methods
in Cardiology
Recorded signals
represent a sum of contributions of electrical
activities of individual cells of the organ
during propagation of excitation.
Electrophysiological Methods
in Cardiology
1) Whole organism (ECG)
2) Isolated heart (Langendorff)
Zipes D. a Jalife J. (2003)
Cardiac Electrophysiology: From Cell To Bedside
3) Multicellular cardiac samples
5) Single membrane channels
4) Isolated cardiomyocytes
Electrophysiological Methods
in Cardiology
1) Whole organism (ECG)
2) Isolated heart (Langendorff)
3) Multicellular cardiac samples
5) Single membrane channels
4) Isolated cardiomyocytes
measured quantities: 1) membrane voltage (V)
potential difference between the extra- a intracellular
medium (across the cellular membrane)
φi φe V = φi - φe
measured quantities : 2) membrane current (I)
Electrophysiological Methods
in Cardiology
BASIC PRINCIPLES OF MEASUREMENTS
ON VARIOUS LEVELS OF ORGANISM
LEVEL OF WHOLE ORGANISM
EKG
recorded quantity: VOLTAGE (as the potential difference)
MAP
(MONOPHASIC
ACTION POTENTIAL)
50 mV
suction electrode
His bundle
electrogram
A
H
V
method: surface and intracardial recording electrodes
His bundle electrogram
SA AV
EKG
EHS
PQ QRS
A H
V
HV conduction time of excitation
through the bundle of His
HVPA
PA conduction time of atrial
excitation
AH
AH conduction time of excitation
through AV node
PQ segment
A
V
P
LANGENDORFF
APPARATUS
recorded quantity: VOLTAGE (as the potential difference)
electrogram
LV
RV
method: electrodes embedded in walls of the bath
closed aortic valve
empty ventricles
aorta
MAP
[mV]
LEVEL OF ISOLATED ORGAN
or the epicardial suction electrode
reference electrode
recorded quantities: membrane voltage
methods: glass microelectrodes
membrane currents
[A]
membrane voltage
[mV]
MULTICELLULAR CARDIAC SAMPLES
‘current clamp’ mode of stimulation
‘voltage clamp‘mode of stimulation
membrane currents
glass
microelectrode
reference Ag/AgCl electrode
Ag/AgCl electrode
TWO ELECTROPHYSIOLOGICAL
METHODS BASED ON
ISOLATION OF CARDIOMYOCYTES
CELLULAR ELECTROPHYSIOLOGY
ENZYMATIC ISOLATION
OF CARDIOMYOCYTES
CONTRACTION
CHARACTERISTIC ELECTRICAL ACTIVITY
(ACTION POTENTIAL and MEMBRANE CURRENTS)
SUCCESSFUL DISSOCIATION
OF CARDIAC TISSUE RESULTS IN …
SUFFICIENT FRACTION OF
VIABLE, FUNTIONALLY UNDAMAGED CELLS
RESPONDING TO ELECTRICAL STIMULATION BY :
ISOLATED CARDIOMYOCYTES
ISOLATED CARDIOMYOCYTES
methods: glass microelectrodes
ISOLATED CARDIOMYOCYTES
methods: glass microelectrodes
Technika patch clamp při měření z celé buňky
(whole cell patch clamp technique)
ISOLATED CARDIOMYOCYTES
methods: glass microelectrodes
recorded quantities: membrane voltage
membrane currents
‘current clamp’ mode of stimulation
‘voltage clamp‘mode of stimulation
[nA]
membrane
currents
[mV]
membrane
voltage
voltage clamp mode
of stimulation
Im
Um
Ic
Ic
current clamp mode
of stimulation
Im
Um
ICa-L
INa
Ito
IK, IK1
ISOLATED CARDIOMYOCYTES
SINGLE MEMBRANE CHANNELS
(molecular level)
glass
microelectrode
recorded quantity: current flowing through single channel
in response to imposed voltage pulse
single channel current
[pA]
methods: glass microelectrode
´patch clamp´ in single channel arrangement
(membrane located inside the tip of microelectrode)
membrane patch
with single channel
Possibilities of Use of These Techniques
Analysis of electrical properties of cardiomyocytes under
physiological and pathological conditions
Analysis of changes of electrical properties of cardiomyocytes
under the effect of drugs
Methods of Analysis of Electrophysiological
Properties of Cardiac Cells
Whole cell patch clamp technique