The autorhythmicity of cardiac pacemaker cells is made possible by the reduced permeability of

Electrical impulses known as action potentials initiate the contraction of the cardiac muscle.
The autorhythmicity of cardiac pacemaker cells is made possible by the reduced permeability of potassium.
 The pacemaker potential is produced by a decrease in membrane permeability to potassium.

Because it spreads quickly 

Well it come be the gain or the carbohydrates and also protein.hopefully it let me know