Section III.Disturbance of Potassium Balance. Potassium Balance (1) Content and distribution (2) Function of potassium (3) Regulation of K + balance Hypokalemia Hyperkalemia. 1. Potassium Balance (1) Content and distribution.
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Section III.Disturbance of Potassium Balance
(1) Content and distribution
(2) Function of potassium
(3) Regulation of K+ balance
After intake a bottle of orange juice (40 mmol/L of K+),
if all K+ stays in ECF, the [K+]e=4.5+2.4=6.9 mmol/L, which will lead to abnormal ECG. Abnormal ECG means the heart muscle is injured.
If all K+ is transported into ICF, the [K+]i=160+1.2=161.2 mmol/L.
Then the excessive K+ will be eliminated within several hours in the urine.
The basic mechanism to the balance is “leak and pump”.
(Integrity of cell membrane and function of Na+-K+ pump)
Na+ - K+泵（泵）
ECF [H+]↑， H+入细胞内，细胞内K+外移。ECF每0.1 pH变化大约引起0.6mmol/L血清钾变化
ECF 渗透压↑ ↑ ，使细胞内K+外移。
ECF [K+] 4.2mmol/L
A decrease in pH of 0.1 units usually elevates the serum [K+] by about 0.6 mmol/L.
(alkalosis: pH ↑ 0.1, [K+] ↓ 0.6 mmol/L)
Insulin promotes the movement of K+ into the liver cells and skeletal muscle cells by increasing sodium-potassium ATPase activity.
The β-adrenergic agonists also elevate Na+ -K+ pump activity to enhance K+ entry.
The α-adrenergic agents enhance the K+ transport out of cells.
Epinephrine stimulates α-recepter first,then β-recepter.
Increased anabolism (AA protein, glucose glucogen) elevates the [K+]i.
Increased catabolism (protein AA, glucogen glucose) reduces the [K+]i.
Decreased water in the cells elevates the [K+]i. The difference [K+]iand [K+]e increases, which leads to the shift of K+ out of cells increases.
(1) opening of ATP-dependent K+ channels
与电压依赖型的钾离子通道不同，也与依赖钙离子的钾离子通道不同，，KATP通道主要受细胞内的ATP浓度调节。在生理条件下细胞内ATP浓度约为3-4 mmol.L-1, KATP通道基本处于关闭状态。只有当心肌细胞发生缺血缺氧，能量耗竭，胞内ATP浓度低于0.2 mmol.L-1时通道开放，K+外流，
(2) decrease Na+ -K+ ATPase activity due to ATP depletion.
High [K+]e activates pump (Na+ /K+ pump) in basolateral membrane, the K+ transport from peritubular interstitial fluid into renal tubular cells will increase.
High [K+]e increases the permeability of lumenal membrane, the K+ transport from renal tubular cells into tubules (urine) will increase.
High [K+]edecreases the [K+] difference between renal tubular cells and peritubular interstitial fluid, then decrease the back-flow of K+ from tubule.
Increased volume and flow rate of urine in distal tubules and collecting ductsreduce the [K+], increase the difference between the [K+] in urine and in tubule cells, increase the excretion of K.
If more negative charges in tubular fluid, more K+ will be excreted.