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Apparently in myocytes, there is an inward rectifier potassium channel that operates in phase 4 of the myocyte action potential. I have heard that while this is named as an inward rectifier, that in-vitro it in fact still transport potassium from the inside to the outside of the cell. However wikipedia seems to suggest otherwise.

Can someone please explain what the inward rectifier potassium channel does and it's role in phase 4 of the myocyte action potential?

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According to Boron's medical physiology textbook:

"Although inward rectifying potassium channels pass current better in the inward than the outward direction, the membrane potential (Vm) is typically never more negative than Ek (equilibrium potential of potassium across the membrane). Thus,net inward K+ current does not occur physiologically. As a result, the activation of GIRK channels (G protein coupled inwardly rectifying potassium channel) hyperpolarizes cardiac cells by increasing K+ conductance or outward K+ current."

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