【文章內容簡介】 (cell membrane is hyperpolarization, hyperpolarizative block). The difference between resting and threshold potential is increased. A greater stimulus is needed to produce an action potential (AP). (b) manifestations ① Effect on skeletal muscles The effects of hypokalemia depend on partly the decrease speed of serum [k+]. The rapidly decreased serum [k+] leads to skeletal muscle weakness, flabbiness (soft), and flaccid (soft) paralysis. The most severe problem of muscular paralysis is ?? ? In chronic potassium depletion, the k+ in ICF moves to ECF, both intracellular and extracellular [k+] are decreased, the ratio of [k+]i to [k+]e is not obviously changed, the resting potential is not changed. ? Chronic potassium depletion may lead to the muscle atrophy (thin and weakness of the muscle) , which is mainly caused by disturbance of protein metabolism. Chronic K deficiency decreases the ATP production and ATPase activity. In severe K deficiency (), during strenuous exercises the cells cannot release enough K to dilate the vessels, which can lead to ischemia and necrosis of muscle cells with energy metabolism disturbance (exertional rhabdomyolysis). ② Effect on SMC gastrointestinal tract, ? Decreased neuromuscular irritability causes: ? decreased intestinal motility, ? abdominal distension, ? anorexia, ? nausea ? constipation. ? bowel sound腸鳴音 disappear, ? paralytic ileus 麻痹性腸梗阻 . ③ Effect on vascular SMC ? Decreased muscular excitability leads to postural hypotension. ? ④ If there are some other electrolytes disturbances at the same time, the manifestations will change. ? Low [k+] leads to more negative of RMP。 ? High [Ca2+] leads to the elevation of TMP. ? (Ca2+ inhabits the Na+ into the cells) ? Low [k+] + High [Ca2+] will increase the distance between the RMP and TMP and cause very low neuromuscular excitability. ? ? Low [k+] + low [Ca2+] will restore the normal distance between the RMP and TMP and cause the normal neuromuscular excitability. Low [k+] leads to more negative of RMP。 Low [Ca2+] leads to the decrease of TMP. Ca2+ ← ———— → bining calcium H+ OH 2) Effect on heart (a)Effects on myocardiac cells a) Arrhythmia b) Abnormal contractibility c) Abnormal electrocardiogram (ECG) ① The excitability of myocardiac cell is increased. ? The potassium permeability of myocardiac cell is reduced in hypokalemia. ? Less K+ moves outside the cell, the RMP is less negative. ? The difference between RMP and TMP is reduced. Smaller stimulus m