Absorption: Passive transport occurs in the small intestine, while active transport occurs in the colon under the influence of aldosterone.
Excretion: Primarily managed by the kidneys in all animals and also through saliva in adult ruminants.
Cellular Distribution: At least 95% of whole-body potassium is intracellular, with skeletal muscle containing 60%–75% of that total.
Biological Function: The potassium gradient generated by Na+/K+-ATPase is the primary driver of the negative electric potential across cell membranes.
Regulation: Aldosterone, released from the adrenal gland in response to hyperkalemia, enhances potassium secretion in the distal renal tubules and collecting ducts.
Hypokalemia (Potassium Deficiency)
Etiology (Causes):
Increased Loss: Renal losses (polyuria, tubular disease), GI losses (vomiting, diarrhea), or iatrogenic loss from large volumes of IV fluid.
Decreased Uptake: GI stasis or sustained decrease in feed intake.
Intracellular Shifts: Translocation into cells due to hyperinsulinemia associated with hyperglycemia.
Clinical Findings:
Mild/Moderate: Often non-specific.
Severe: Generalized muscle weakness leading to recumbency, ventroflexion of the head, and cardiac arrhythmias (atrial and ventricular premature complexes).
Chronic: Prolonged, profound deficiency can result in difficult-to-treat myopathy.
Species-Specific Notes:
Cats: Affected by feline hypokalemic polymyopathy; Burmese cats have an autosomal recessive disorder leading to hypokalemic myopathy.
Dogs & Cats: Can be caused by hyperaldosteronism.
Hyperkalemia (Potassium Excess)
Primary Causes:
Reduced Excretion: Inadequate urinary excretion due to hypovolemia, urinary tract obstruction, or bladder rupture.
Muscle Release: Potassium release into the blood from exertional rhabdomyolysis in horses and ruminants.
Endocrine: Frequently occurs in dogs with hypoadrenocorticism.
Genetic Factors: Identified as hyperkalemic periodic paralysis in heavily muscled Quarter Horses and related breeds.
Clinical Findings:
Generalized muscle weakness and depression.
Cardiac Conduction Disturbances: Can progress to lethal cardiac arrhythmias.
Diagnostic Nuances
Whole Body Status: Serum concentrations do not always reflect total body status; for example, animals with acidemia may show hyperkalemia despite being whole-body depleted.
Pseudohyperkalemia: Occurs in serum or plasma due to hemolysis, as red blood cells in most species have high potassium concentrations.
Species Variation: Some species possess genetic differences in their erythrocytic potassium concentration, which can affect diagnostic results.