Cellular And Molecular Events Flashcards
What do action potentials trigger in cardiac myocytes?
Increases in cystolic calcium.
Describe the shape of the ventricular action potential:
Voltage gated sodium channels open and there is sodium influx which gives a sharp peak. There is then a little drop in membrane potential due to opening of K channels. There is a small decrease as calcium influx occurs and then these channels inactivate and the membrane potential is reached after the voltage gated K+ channels open and there is K+ efflux.
What is the name of the slow rise in membrane potential during the action potential on the sino-atrial node?
Funny current.
What ion channel is responsible for the funny current?
Na channels.
In the sinoatrial node action potential, state which channel is responsible for each the upstroke and the downstroke.
Upstroke: calcium channels, downstroke: potassium channels
Why aren’t voltage gated Na channels responsible for the funny current? What channel opens instead?
These would inactivate and therefore there would not be sufficient Na influx. HCN channels.
What is a HCN channel?
Hyper polarisation activated cyclic nucleotide gated channel
What property of the sinoatrial node means that it sets the heart rate?
It is the fastest to depolarise
Where are nuclei positioned In cardiac muscle?
They are singly and centrally located.
Name two features which differentiate cardiac muscle from other kinds of muscle
Branching and gap junctions
What is the purpose of gap junctions in cardiac muscle?
They allow ion move,net across them and so electrically couple the cells.
Name the two ways in which cystolic calcium increases during the ventricular action potential.
L-type calcium channels in the t tubule system permit movement of calcium across the sarcolemma and CICR channels permit movement of calcium out of the SR.
What happens to cystolic calcium after muscle contraction?
It is pumped back into the SR by SERCA to maintain the calcium store.
What pumps in the membrane cause calcium efflux after contraction?
Na/Ca exchanger and sarcolemma Ca ATPase
What cells are responsible for the tone of blood vessels?
Smooth muscle cells in the tunica media.
Name two causes of excitation-contraction coupling in smooth muscle cells:
Depolarisation which allows Ca to enter the cell by voltage gated Ca channels
Noradrenaline which binds to a1 receptors and releases IP3 which acts on SR leading to increased calcium.
How does increased calcium lead to contraction in smooth muscle cells?
Calcium binds to calmodulin which activates myosin light chain kinase which phosphorylates the myosin heads and means they can. Interact with actin.
How does smooth muscle contraction stop as calcium levels decline?
Myosin light chain phosphotase dephosphorylates the myosin light chain so it can no longer interact with the actin filaments.
What molecule can phosphorylate myosin light chain kinase and what does this cause?
Protein kinase A. Inhibits action of MLCK and so there is increased vasomotor tone.
