creatine kinase Flashcards
What is a myocardial infarct?
Why do the cells die?
Why is there a lack of oxygen?
it is the death of heart muscle cell
Lack of oxygen.
Blockage of the cardiac arteries. This process is termed atherosclerosis
Why do cells need oxygen and how do they use it?
why do cells die without it?
cells have a semi-permeable membrane separating the inside from the outside
active exclusion of some things such as Na+ ions.
This needs a protein pump in the membrane called membrane ATPases, a type of enzyme.
They use energy in the form of adenosine triphosphate (ATP) to pump ions.
ATP is generated Via glycolysis, the Krebs Cycle and oxidative phosphorylation
The end point of the process requires atmospheric oxygen, hence if there is less oxygen supplied to a cell there is less ATP, pumps do not function, ion balance is lost and cells die.
Why does serum CK indicate cell death?
Cell contents are released when they are dying, i.e. proteins that should be held inside against concentration gradients appear in the serum.
Therefore the levels of many proteins including creatine kinase (many others as well such as lactate dehydrogenase) in serum can be used as indirect indicators of cell death.
Where is Creatine Kinase (CK) normally present?
CK is present in all cells at very low levels but is at high concentrations in metabolically very active tissues including the brain, heart and skeletal muscle. Creatine phosphate is an energy store.
how can you determine CK activity?
what are the reactions to achieve this?
CK activity in the serum can be detected by a coupled assay leading to the generation of detectable products.
creatine phosphate+ ADP -> creatine and ATP
D-glucose + ATP -> G6P + ADP
G6P + NADP+ -> (NADPH+) + 6-PG + H+
NADHP (and NADH) have an absorption spectra distinct to NAD+
What is the structure of CK?
why can the isoforms be separated by electrophoresis?
CK is a protein made from two subunits or monomers
Monomers associate and bind to one another in the cytoplasm to produce active dimers
The two monomers are coded for by two different genes.
so there are two different monomer isoforms “B” and “M”.
The two monomers have approximately the same molecular weigh (43 kDa) but differ in their Isoelectric point (the pI for the B isoform is 6.77, while the pI for the M isoform is 5.34).
How can increased CK be related specifically to the death of cardiac muscle rather than skeletal muscle and brain tissue?
The Brain only expresses the B gene and hence makes only B monomers and so only the BB form can be generated.
MM form is the only one made in skeletal muscle cells (useful in diagnosis of the extent of skeletal muscle damage in muscular dystrophies).
both genes are expressed in cardiac muscle cells so they make all three dimers including the hybrid BM form.
Thus, death of cardiac muscle fibres can be determined if the BM isoform of CK can be detected in the serum.
is the levels of serum CK BM isoform in proportional to the amount of cell death?
Why?
levels of CK BM isoform in the serum are directly proportional to the amount of cell death in the heart.
This is because each myocyte can be considered to be approximately of equal volume (they have equal likelihood of dying independently of their size) so, as each cell dies it releases a “quantum” of CK into the extracellular fluid and thence into the serum.
So, is a simple measure of CK activity in serum a sufficiently good diagnostic test for myocardial infarct”?
In general how might you experimentally discern between different protein isoforms, what methods can be used?
No, because the activity could be from any of three tissues. Assay of the BM form is essential.
Electrophoresis or column chromatography
they can separate on the basis of molecular weight or charge
but are slow and require expert technical operation. Neither are ideal in a Casualty Department.
An immunological approach? What other way can individual proteins be discriminated?
can this method alone be used to determine if an infarct has occurred?
artificial manufacture of antibodies against desired proteins
eg a specific antibody that recognises the BM isoform.
Using this type of antibody, commercial kits for the quantification of the BM isoform of CK are now available from a number of suppliers for clinical diagnostic use.
No, this test would be given along with many others and would never be used alone to determine if an infarct had occurred
it is used to determine how big the infarct is
and by changes in levels of CK approximately how long ago the infarct occurred.
What is the time course of CK, SGOT and LDH after myocardial infarction?
CK- 1 day
SGOT- 2 days
LDH- 5 days
What other markers can be used for diagnosis of myocardial damage?
What makes cardiac troponin good for this purpose?
Serum glutamate oxaloacetate transaminase (SGOT)
lactate dehydrogenase (LDH)
Cardiac troponin
Troponin is the calcium switch in muscle. Cardiac troponin I and troponin T are tissue specific and are not present in any other muscle. Their presence in the serum represents a specific marker for cardiac infarction (typically appearing in the serum after 48h of infarction and persisting for approximately 5 days).
what proportion of CK is CK-MB
what proportion is MM
where is Ck usually found?
15%
85%
all cells at low levels, but metabolically active cells eg muscle, brain, heart in high conc
