Basic hyperpolarization/depolarization cardio

[chromuffin]

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This is really basic and I don't know why I don't understand this, but why is an increase in extra cellular K+ causing cardiac cells to depolarize? I've always thought K+ efflux repolarizes the cell. My prof says that since cardiac cells are selectively permeable to K+ at rest, an increase in extracellular K influences cells to depolarize.

Am I just missing some basic concept?

The instructor used the Nernst equation in the discussion, but I don't get it.

 

[Merely]

More k outside cell means the k inside the cell has less incentive to leave the cell since less concentration gradient. Less k leaving the cell means more k in the cell. More k in cell depolarizes cell since k is positively charged.

 

[chromuffin]

More k outside cell means the k inside the cell has less incentive to leave the cell since less concentration gradient. Less k leaving the cell means more k in the cell. More k in cell depolarizes cell since k is positively charged.

Gotcha. So it references the gradient in which K will flow. So hypokalemia causes repolarization as a result of potassium leaving the cell to equilibrate; hence, problems like long QT syndrome.