Essay: With its citations, explain the chemical basis of the resting membrane potential?

The resting membrane potential (RMP) is a fundamental concept in physiology that refers to the electrical potential difference across the plasma membrane of a cell at rest. It is crucial for the proper functioning of excitable cells, such as neurons and muscle cells, as it allows for the generation and propagation of electrical signals. The RMP is primarily established and maintained by the selective movement of ions across the cell membrane, which is governed by the principles of electrochemical gradients and ion channels.

At the molecular level, the RMP is determined by the distribution of ions, particularly sodium (Na+), potassium (K+), and chloride (Cl-) ions, across the cell membrane. The concentration gradients of these ions are established and maintained by various ion pumps and channels. The Na+/K+ ATPase pump, for instance, actively transports three Na+ ions out of the cell and two K+ ions into the cell, consuming ATP in the process. This pump helps maintain a higher concentration of K+ ions inside the cell and a higher concentration of Na+ ions outside the cell, contributing to the establishment of the RMP.

In addition to the Na+/K+ ATPase pump, ion channels play a crucial role in establishing and maintaining the RMP. These channels are selective for specific ions and can be either leak channels, which are always open, or gated channels, which can be opened or closed in response to various stimuli. The opening and closing of these channels allow for the movement of ions across the cell membrane, thereby influencing the RMP.

For example, potassium leak channels, also known as K+ channels, are responsible for the passive movement of K+ ions out of the cell. This movement is driven by the concentration gradient established by the Na+/K+ ATPase pump. As K+ ions move out of the cell, they leave behind negatively charged proteins and other anions, creating an excess of negative charge inside the cell. This excess negative charge attracts K+ ions back into the cell, creating an equilibrium where the movement of K+ ions out of the cell is balanced by their movement back into the cell. This equilibrium potential for K+ ions is known as the K+ equilibrium potential or the Nernst potential.

Similarly, other ion channels, such as Na+ channels and Cl- channels, also contribute to the establishment of the RMP. The movement of Na+ ions into the cell is limited by the closed state of Na+ channels, preventing the RMP from reaching the equilibrium potential for Na+ ions. Cl- ions, on the other hand, move into or out of the cell depending on the concentration gradient and the electrical potential across the membrane.

Overall, the resting membrane potential is a complex phenomenon that relies on the selective movement of ions across the cell membrane. The concentration gradients established by ion pumps and the opening and closing of ion channels play a crucial role in determining the RMP. Understanding the chemical basis of the RMP is essential for comprehending the electrical properties and functions of excitable cells.

Citations:
1. Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2002). Molecular Biology of the Cell. Garland Science.
2. Purves, D., Augustine, G. J., Fitzpatrick, D., Hall, W. C., LaMantia, A. S., McNamara, J. O., & White, L. E. (2018). Neuroscience. Sinauer Associates.