slowing down action of Na[sup]+[/sup]/K[sup]+[/sup] ATPase

[HotHamH2O]

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Question reads: Digitalis is a drug that strengthens heart contractions in patients with heart failure. The drug exerts its effect by slowing down the action of the Na⁺/K⁺ ATPase. One of the side effects of digitalis is an increase in cardiac arrhythmias, or cardiac musicle "twitchiness". Based on the mechanism of action of digitalis, the arrhythmias are most likely due to:

A. a slight depolarization of cardiac muscle cells.
B. an increase in Ca²⁺ entry into cardiac muscle cells.
C. an excess of ATP
D. an increased rate of repolarization

A is the answer. The explanation says that the slowing of the ATPase would cause less sodium to be pumped out of causing a slight depolarization of the resting potential and therefore bringing it closer to threshold (twitchiness).

My question is, if the ATPase is slowed wouldn't it not only slow the pumping out of sodium but also the pumping in of potassium and therefore maintain equilibrium?

 

[ipmed]

You have to consider the OTHER ION (CA+). Calcium will build up in the cardiac muscle; the main cause of contraction in the heart. additionally, the Na/K gradient is used for A.P. & Calcium causes Contractions

 

[HotHamH2O]

You have to consider the OTHER ION (CA+). Calcium will build up in the cardiac muscle; the main cause of contraction in the heart. additionally, the Na/K gradient is used for A.P. & Calcium causes Contractions

Ok. Can you explain further. I understand everything you said, but I do not understand how if the pump is slowed down the resting potential will increase.

 

[dollarbill]

think of an AP in a neuron, when you have an influx of NA+ you get depolarization. When admin Dig you halt the NA/K ATPase which is just like increasing the influx of NA+. Also, remember the ATPase is 3NA out to 2K in so overtime NA builds up in cell. Hope that maybe cleared it up