Atrial natriuretic peptide enhances activity of potassium conductance in adrenal glomerulosa cells

Aldosterone secretion from the adrenal glomerulosa (AG) cells is inhibited by atrial natriuretic peptide (ANP). Inasmuch as alterations in K⁺ conductance can modulate aldosterone secretion, the effect of ANP on intracellular K⁺ homeostasis was investigated. Intracellular K⁺ concentration ([K⁺](i)) of AG cells was assessed by spectrofluorometry using the K⁺-sensitive dye, K⁺-binding benzofuran isophthalate. The resting value of [K⁺](i) in AG cells was determined to be 120 ± 1.2 mM (n = 37) in a HCO₃-free, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium. Exposure of AG cells to ANP led to a dose-dependent, transient decrease in [K⁺](i), from 21 ± 3.2% (n = 7) at 100 pM to 31 ± 2.3% at 1 μM (n = 7). In the continued presence of ANP, a rapid recovery to near basal values of [K⁺](i) was attained within 90 s. Measurements of membrane voltage using the potential sensitive dye 1-3 (-sulfonatopropyl)-4-{β-(-(di-n- butylamino)-6-naphthyl)vinyl}-pyridinium betaine documented an accompanying change in membrane potential. Pretreatment of AG cells with barium (0.5 mM), tetraethylammonium (0.1 mM), charybdotoxin (100 nM), or ethylene glycol- bis(β-aminoethylether)-N,N,N',N'-tetraacetic acid (0.5 mM) blunted the ANP- induced decrease in [K⁺](i). ANP-(7-23), the ANP-C-receptor selective agonist, which does not elevate guanosine 3',5'-cyclic monophosphate (cGMP) did not alter [K⁺](i) in contrast to cGMP (50 μM), which did. We conclude that ANP via the activation of the ANP A receptor alters K⁺ homeostasis through a Ca²⁺-activatable K⁺-conductive pathway likely to be the maxi-K channel.