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The kidney is the primary organ ensuring K +  homeostasis. K +  is secreted into the urine in the distal tubule by two mechanisms: by the renal outer medullary K +  channel (K ir 1.1) and by the Ca 2+ -activated K +  channel (K Ca 1.1). Here, we report a novel knockout mouse of the β 2 -subunit of the K Ca 1.1 channel (KCNMB2), which displays hyperaldosteronism after decreased renal K +  excretion. KCNMB2 −/−  mice displayed hyperaldosteronism, normal plasma K +  concentration, and produced dilute urine with decreased K +  concentration. The normokalemia indicated that hyperaldosteronism did not result from primary aldosteronism. Activation of the renin-angiotensin-aldosterone system was also ruled out as renal renin mRNA expression was reduced in KCNMB2 −/−  mice. Renal K +  excretion rates were similar in the two genotypes; however, KCNMB2 −/−  mice required elevated plasma aldosterone to achieve K +  balance. Blockade of the mineralocorticoid receptor with eplerenone triggered mild hyperkalemia and unmasked reduced renal K +  excretion in KCNMB2 −/−  mice. Knockout mice for the α-subunit of the K Ca 1.1 channel (KCNMA1 −/−  mice) have hyperaldosteronism, are hypertensive, and lack flow-induced K +  secretion. KCNMB2 −/−  mice share the phenotypic traits of normokalemia and hyperaldosteronism with KCNMA1 −/−  mice but were normotensive and displayed intact flow-induced K +  secretion. Despite elevated plasma aldosterone, KNCMB2 −/−  mice did not display salt-sensitive hypertension and were able to decrease plasma aldosterone on a high-Na +  diet, although plasma aldosterone remained elevated in KCNMB2 −/−  mice. In summary, KCNMB2 −/−  mice have a reduced ability to excrete K +  into the urine but achieve K +  balance through an aldosterone-mediated, β 2 -independent mechanism. The phenotype of KCNMB2 mice was similar but milder than the phenotype of KCNMA1 −/−  mice.

Hyperaldosteronism after decreased renal K+excretion in KCNMB2 knockout mice

Hyperaldosteronism after decreased renal K⁺excretion in KCNMB2 knockout mice