potassium

• a cation
• the most important intracellular osmolyte
• alterations in extracellular K+ influence membrane potential
((hypokalemia => high threshold; hyperkalemia => low threshold))

[[renal handling of K+]]
• obligate reabsorption of K+ at PCT and aLOH
• the DCT and CCD may be net reabsorptive or net secretory
○ secretory activity is enhanced by aldosterone ((acting at principle cells))

((hyperkalemia))
• concentration and electrical gradients power K+ secretion
• low filtrate flow will impede K+ secretion
• decreased lumen negativity => decreased K+ secretion
○ “Why might hyperkalemia occur in animals with postrenal azotemia?”

((hypokalemia))
○ “How does K+ get reabsorbed at the DCT/CCD?”

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