cyhuang
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I got a few question about the effect of potassium concentration:
As far as I know, hyperkalemia causes the resting membrane potential to be more negative, so that makes an action potential harder to achieve. And hypokalemia causes the resting membrane potential to be more positive, so that makes an action potential easier to achieve.
(correct me if I were wrong.)
Here are my questions:
1.If the former statements were correct, than it would explain why hyperkalemia causes muscle weakness, paralysis, and cardiac depression(no action potential, no muscle contraction). But what's the reason that hypokalemia causes muscle weakness,too?
2.How to explain the ECG finding of hyper- and hypokalemia? ( Hyperkalemia: shallow, wide QRS with tenting T wave; Hypokalemia: low T wave)
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| ssrpk
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hyperkalemia depolarizes the memebrane...
hypokalemia hyperpolarizes the membrane...
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| phuluong2k
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At resting membrane, concentration of K in the cell is very high, and in the extra-cellular fluid is slow :arrow: there is a passive flow of K out of the cell
:arrow: Hyperkalemia, extracellular K is high :arrow: prevent the passive flow :arrow: more K in the cell :arrow: depolarization
:arrow: Hypokalemia, extracellular is slow :arrow: stimulate passive flow :arrow: more K goes out of cell :arrow: hyperpolarization
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| bighear
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I absolutely agreed what you mentioned above. But do anyone know what is the mechanism of the followlin sentence--->[Hypokalemia, as predicted by the Nernst equation, hyperpolarizes the resting membrane potential to more negative values, and consequently may cause slowing of conduction . In addition, hypokalemia decreases potassium conductance and may enhance automaticity] . I confused that hypokalemia decreases potassium conductance but enhances automaticity.
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| mildus
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Effects of hyperkalemia:
1. increased excitability due to decreased resting membrane potential (less negative potential, so closer to the treshold value)
2. decreased amplitude of action potential (amplitude is measured from the resting value to the spike value, and with hyperkalemia the resting value is decreased and so as the amplitude)
3. the main effect is: due to decreased potassium concentration gradient, repolarization is prolonged (refractory period is prolonged) so the frequency of action potentials is decreased
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| ssrpk
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here is wht i found in katzung !
tht's a nice explanmation by mildus, just to add!
a/c to bighear he is right to say tht potassium concentration hasa more to do with the permeability rather than resting membrane potential!
Hyperkalemia: reduces eq. potential for K+ but on the other hand increases permeability therefore potassium current will be higher and RMP will come closer to K+ eq. potential!
significance: in cardiac pacemaker cells during phase IV ,due to high K+ permeability it will effectively counteract hyperpolarization induced depolarizing current via rectifier channels therefore late approach towards threshold!
Hypokalemia: increases eq. potential for K+ but on the other hand reduces permeability ;therefore K+ current will be low and RMP will be farther away from the eq. potential (K+ eq. pot. has the major influence on RMP) in other words membrane will be destabilized!
significance: in cardiac pacemaker cells low K+ current during phase IV will not be able to effectively counteract the depolarizing current and therefore early approach towards threshold [enhanced automaticity]
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