Question

what would happen to the charge across the cell membrane outside cell potassium concentrations are greatly increased by KCL injection into the blood

Answer 1

Cell membrane potential is largely determined by the concentration of Potassium ions inside the cell. A neuronal cell, for example has a resting potential of about -75mV, therefore the cell membrane is highly permeable to K+. The more K+ continues to flow, the more charge will be separated and greater will be the potential difference. Because the neuronal membrane at rest is mostly permeable to K+, the membrane potential is close to equilibrium. Another consequence of high K+ permeability is that the membrane potential is particulalrly sensitive to changes in the concentration of extracellular potassium. A tenfold change in the K+ concentration oustide the cell from 5 to 50mM, would change the membrance potential from -75 to -17mV. A change in membrane potential from the normal resting value (-75mV) to a less negative value is called depolarization.

If the potassium concentrations are greatly increased by KCl injection into the blood, it will cause depolarization of the cell membrane of the neuronal cells, skeletal muscle cell, cardiac cells etc. Although neurons in the brain are somewhat protected from large changes in [K+]o, other excitable cells in the body, such as muscle cells are not. Without negative resting potentials, cardiac muscle cells can no longer generate the impulses that lead to contraction and the heart immediately stops beating. Intravenous potassium chloride is, therefore, a lethal injection.