Question

In cases of renal failure, plasma (extracellular) concentrations of K+ may increase from normal levels of 4-5 mM. From what you know of the effects of increasing extracellular K+ on the membrane potential and the effects of membrane potential on the HCN channel, you would expect the increased extracellular concentration of K+ to:

a. decrease heart rate

b. decrease cardiac output

c. depolarize the resting membrane potential in the pacemaker cells

d. all of the above are correct

e. only a and b are correct

Answer 1

D.All are correct

Hyperkalemia is the state of the serum potassium level >5Mm/L. Here, it occurs due to decreasesd excretion of the K+ by kidneys due to renal failure and Extracellular shift of K+ ions.

As the extracellular K+ ion concentration increases, there will be reduction in the magnitude of the K+ ion gradient across the cell, and so is the absolute value of the resting membrane potential.The membrane voltage become less negative, moving closer to the threashold potential making it easier to initiate an action potential. This ends up in decrease of myocyte excitability, due to the value of the membrane potential for onset of an action potential to termins the number of voltage gated Na+ channels activated to depolarization.As this value becomes less negative in hyperkalemia,the number of avilable Na+ channels decreases, resulting in a slower influx of Na+ and subsequently slower impulse conduction.

Hence the ECG will show a sinusoidal by non existence of P wave(widens and flattens), R wave will be reduced(QRS complex widens) and blends with T wave, S wave will show a depression. The higher the K+, Depolarization happens due to low K+ conductance, Hyperpolarization due to inactivated Na+ channel, and Reduced membrane excitability.

Finally casing:

1. Repolarization defects
2. Conduction delay
3. Paralysis of atria
4. Ventricular rhythms.