If we were able to artificially alter the membrane permeability of pacemaker cells so that sodium influx is more rapid, . A) threshold is reached more quickly and heart rate would increase B) potassium channels compensate and no change in heart rate would occur C) heart rate would decrease, but blood pressure would rise due to the excess sodium present D) tetanic contraction would occur due to the short absolute refractory period of cardiac muscle

The answer is A.

Explanation:

The permeability of the pacemaker cell's membrane is the factor that controls the density of the materials inside the cell which also includes sodium and that controls the neurons and muscles. So if we were able to artificially alter the pacemaker cell's membrane parmeability, for the heart it would result in a quicker satisfaction of the threshold value and therefore would increase the heart rate.

I hope this answer helps.

A,

Explanation

Increase membrane permeability  to rapid  sodium influx  leads   to  fast depolarization.With continuous rapid opening now ,  threshold  will be reached onetime.

Hence  fast  propagation of action potential occurs . since reploarization and refractive period now shortened, due to increase  rate of depolarization .Rapid action potential will be propagated and transmitted in  the  cardiac cells. Leading contraction rapid  systolic  contraction.

Increase in sodium  ion concentration in the cardiac cells  leads to retention of fluids( the high solute potential draws water in from surrounding tissues and plasma by osmosis) in the  cardiac muscles cells. This leads to increase in blood pressure, and the  increasing after load leads to rapid heart rate.