Extracellular Potassium On Spontaneous Cintraction Frequency Of Rat Myocytes Flashcards
What is the langendorff perfusion technique ?
It is retrograde perfusion technique via the aorta and coronary circulation
- used to isolate single cardiac myocytes
- heart is perfused with physiological saline solution and collagenases to separate the heart cells
- once the heart cells have de. Isolated the ventricular cells are no longer under the control of the SAN so they don’t contract normally they only undergo spontaneous contractions
How is electrical activity propagated through the heart?
1- SAN initiates the action potential which spreads across atria to the AVN
2- action potential slows down pass through the AVN
3- action potential is rapidly propagates down the bundle of his and bundle branches to the apex of the heart
4- action potential spreads through the ventricles from the apex towards the base via the purkinje cells
5- eventually the heart return to their resting state
In the experiment a spontaneous % of contractions was plotted against the extracellular potassium concentration, what did the graph look like ?
Produced a relatively linear relationship because as the extracellular potassium concentration increased the number of spontaneous contractions increased
In the experiment spontaneous % contractions was plotted against the membrane potential of potassium, what did the graph look like ?
Graph remains flat up until about -50mV where there is a sudden increase because of the change in potassium equilibrium potential
Why were control values taken for each reading during the experiment ?
Because as the experiment went on the cells start to die off and become less viable due to being left at room temperature therefore the results which were produced were still reliable at the different potassium ion concentrations
Why does potassium increase the frequency of spontaneous contractions ?
As the extracellular potassium concentration increases the membrane potential increases from -84mV to more positive values
Initially this depolarisation causes the opening of sodium channels causing influx of sodium ions which increases the frequency of action potentials
The sodium/calcium exchanger is also activated and this is electrogenic so it causes an additional 1+ charge in the direction of sodium ions
How does the sodium/calcium exchanger work ?
The exchange moves 1 calcium ion for 3 sodium ions which means there is a difference of a 1+ charge making it electrogenic
The direction of transport is dependent upon the membrane potential
If the membrane potential is greater than or equal to -40mV the sodium/calcium exchanger moves calcium into the cell
This can cause a calcium overload of the sarcoplasmic reticulum causing spontaneous release of calcium ions from the SR
