Molecular biologists perform a series of experiments to characterize the electrophysiologic properties of human muscle cells. The resting membrane potential for an isolated muscle cell is determined to be -70 mV. The equilibrium potentials for important ions under normal physiologic conditions are as follows:E_Na = + 60 mV
E_K = - 90 mV
E_Cl = - 75 mV
E_Ca = + 125 mV
E_Mg = 0 mVIf physiologic conditions are maintained, which of the following ions would most likely flow out of the cell after opening of their respective ion channels?

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11ec160b_36bb_2bc5_9249_1314f63d3a4a_MD0001_00 Na⁺, K⁺, and Cl^- are the main ions that determine the electrical potential difference (voltage) across a membrane (membrane potential). Under normal physiologic conditions, there is a low concentration of Na⁺ and Cl^- in the cell and high concentration of K⁺ in the cytoplasm. Conversely, the extracellular space has a high concentration of Na⁺ and Cl^- ions and low concentration of K⁺ ions. Because intracellular K⁺ concentration is much greater than its extracellular concentration, opening of cellular potassium channels leads to K⁺ efflux from the cell along the K⁺ concentration gradient. Within the cell, the positive charge of the K⁺ ions is normally neutralized by the negative charge of intracellular anions (eg, phosphates and proteins) that are trapped in the cell. As K⁺ ions leave the cell, negatively charged anions accumulate along the inner side of the cell membrane. This continually increasing negative charge attracts the positively charged K⁺ ions back into the cell. When the difference in concentration (diffusion potential) of K⁺ inside and outside the cell is large, the efflux of K⁺ ions will continue despite the increasing negative charge. At a certain point, however, the negative intracellular charge (electrical potential) of the membrane becomes large enough that the number of K⁺ ions it attracts into the cell equals the number of K⁺ ions that leave the cell along the concentration gradient. The electrical potential difference that moves K⁺ ions into the cell at the same rate as they leave the cell along the concentration gradient is called the equilibrium potential. Educational objective: When a specific ion channel opens, the respective ions will flow across the membrane in a direction that brings the resting membrane potential closer to that ion's equilibrium potential. __________ References: Generation of resting membrane potential. (http://www.ncbi.nlm.nih.gov/pubmed/15545342)

Molecular Biologists Perform a Series of Experiments to Characterize the Electrophysiologic