Flashcards in Cellular and Molecular Events in the CVS Deck (79)
Does Na/K-ATPase set the RMP?
What happens to RMP if the sodium pump is blocked?
It only changes by 5-7mV
What is the RMP set by?
Due to K permeability of the cell membrane at rest
What state are K channels in at rest?
What channels do cardiac myocytes possess?
Inward rectifier K channels
How permeable to other ions are cardiac myocytes?
Only a small permeability
What can be said of cardiac myocytes?
They are electrically active
What is meant by cardiac myocytes being electrically active?
They fire action potentials
What do action potentials trigger?
An increase in cytosolic [Ca]
What is a rise in calcium required for?
To allow actin and myosin interaction
What does actin and myosin interaction generate?
How do action potentials in heart cells differ from those in nerves and skeletal muscle?
They are much longer
What are the stages in the ventricular (cardiac) action potential?
Opening of voltage gated Na channels causes a rapid depolarisation, from RMP to +30mV as Na enters the cell
Transient outward K current causes a return towards a lower membrane potential, reaching +10mV
Membrane potential lowers to about -10mV because of opening of voltage gated Ca channels
Ca channels inactivate and voltage gated K channels open, causing return to RMP
What is rapid depolarisation due to opening of Na channels called?
What might happen after the initial depolarisation that contributes to a lower membrane potential?
Might get some reversal of Na/Ca transport
What may also happen when the voltage gated Ca channels are open?
May be some K channels open, allowing efflux of K
What do cardiac myocytes possess lots of different types of?
Draw the ventricular action potential
Why do cardiac myocytes have lots of different types of K channels?
Because they each behave in a different way, and contribute differently to the electrical properties of the cell
What is the SA nodes set membrane potential?
Doesn’t really have one
Why does the SA node not really have a set membrane potential?
Because the whole time, there is a long, slow depolarisation
What is the SA nodes long, slow depolarisation called?
The pacemaker potential
What causes the pacemaker potential?
Influx of Na
What happens as Na channels open?
Na ions go in to cause a little bit of depolarisation, but become inactivated in accommodation due to long depolarisation
What is the result of the Na channels becoming inactivated by the long depolarisation?
The upstroke cannot rely on Na channels, it also needs voltage gated Ca channels
What is the initial slope to threshold of the SA node action potential known as?
The funny current
When is the SA node action potential activated?
When it reaches membrane potentials that are more negative than -50mV
What is the result on the SA node action potential when the membrane potential reaches a more negative level?
The more it activates
What channels does the funny current use?