Bathmotropic - Physiological Explanation

Physiological Explanation

The bathmotropic effect modifies the heart muscle membrane excitability, and thus the ease of generating an action potential. The easiness of generating an action potential is related both to the magnitude of the resting potential and to the activation state of membrane sodium channels. (For a complete description of the membrane action potential please see the related Wikipedia article on action potentials.) During stage 4 of the action potential, the inside of the cardiac muscle cell rests at −90 mV. As the inner muscle cell potential rises towards −60 mV, electrochemical changes begin to take place in the voltage-gated rapid sodium channels, which permit the rapid influx of sodium ions. When enough sodium channels are opened, so that the rapid influx of sodium ions is greater than the tonic efflux of potassium ions, then the resting potential becomes progressively less negative, more and more fast gated sodium channels are opened, and an action potential is generated. The electrical potential at which this occurs is called the threshold potential. As various drugs and other factors act on the resting potential and bring it closer to the threshold potential, the action potential is more easily and rapidly obtained. Likewise, when the sodium channels are in a state of greater activation, then the influx of sodium ions that allows the membrane to reach threshold potential occurs more readily. In both instances, the excitability of the myocardium is increased.