calculate the resting membrane potentials for both neurons and cardiac myocytes. Make sure to include calculations for both hyperkalemia and normal plasma ion concentrations
JH, a 53 year-old female, had not been feeling well lately and suddenly started to feel acutely worse. She started to have shortness of breath, and was experiencing an irregular heartbeat, chest pain, muscle weakness, and feelings of severe nausea. She called 911 and was taken to the hospital where blood samples were drawn. The following table summarizes the results of her bloodwork (Table 1)
Table 1: JH ion concentrations at intake (blood).
| lon | Plasma concentration - measured (mM) | Plasma concentration - normal (mM) |
| K+ | 8 | 5 |
| Na+ | 142 | 142 |
| Cl- | 105 | 105 |
| Ca2+ | 2.5 | 2.5 |
JH was diagnosed with hyperkalemia and ordered IV fluids. The IV fluids she was given contained calcium gluconate and insulin. Her potassium levels were monitored over a 24-hour period and were as summarized in Table 2.
Table 2. JH potassium concentrations post-IV fluids (blood).
| Time (hours) | Measured plasma K+ (in mM) |
| 0 | 8.0 |
| 3 | 7.1 |
| 6 | 6.4 |
| 9 | 5.9 |
| 12 | 5.6 |
| 15 | 5.3 |
| 18 | 5.1 |
| 21 | 5.0 |
| 24 | 5.0 |
2. Using Table 4, which contains the relative ion permeabilities for neurons and cardiac myocytes at rest,
calculate the resting membrane potentials for both neurons and cardiac myocytes. Make sure to include
calculations for both hyperkalemia and normal plasma ion concentrations
Hint: Use the Goldman equation: V_m = 61 * log((P_Na[Na^+]_o + P_K[K^+]_o + P_Cl[Cl^-]_i) / (P_Na[Na^+]_i + P_K[K^+]_i + P_Cl[Cl^-]_o)). Remember that the intracellular vs. extracellular concentrations of Cl- are flipped to account for its negative charge!
Table 4: Relative ion permeabilities for neurons and cardiac myocytes.
| Ion | Neuron relative permeability |
Cardiac myocyte relative permeability |
| K+ | 1 | 1 |
| Na+ | .04 | 0 |
| Cl- | .45 | 0 |
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