The membrane of the myocardium is affected because of the high concentration of potassium in the extracellular space causing despolarizations and, finally, the channels of Na+ closes in a protective measure. So, I would like to know how calcium reestablish the normal concentration of ions intra and extracellular.
As Marco says, calcium gluconate (the classical treatment to reduce cardiac muscle excitability in hyperkalaemia) does not affect the intra and extracellular concentrations of K+. The NaV1.5 cardiac voltage gated sodium channel is modulated strongly by both intracellular calcium (via CaMKII) and extracellular calcium via a separate mechanism (see the link for a PNAS paper on that). The net effect is a more positive threshold for the NaV1.5, so limiting the chance of inappropriate activation, though effects of calcium on other channels and the sodium calcium exchanger may also play a role. .
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1450128/
Simply, calcium doesn't change K concentration but Calcium restores the difference between resting potential and threshold potential. So it antagonizes cardiac effects of hyperkalemia.
I think you could appreciate to read the paper attached (by Fernando Schiraldi. Look for him on researchgate !)
Marco
As Marco says, calcium gluconate (the classical treatment to reduce cardiac muscle excitability in hyperkalaemia) does not affect the intra and extracellular concentrations of K+. The NaV1.5 cardiac voltage gated sodium channel is modulated strongly by both intracellular calcium (via CaMKII) and extracellular calcium via a separate mechanism (see the link for a PNAS paper on that). The net effect is a more positive threshold for the NaV1.5, so limiting the chance of inappropriate activation, though effects of calcium on other channels and the sodium calcium exchanger may also play a role. .
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1450128/
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