ATRIAL-NATRIURETIC-PEPTIDE ENHANCES ACTIVITY OF POTASSIUM CONDUCTANCEIN ADRENAL GLOMERULOSA CELLS

Aldosterone secretion from the adrenal glomerulosa (AG) cells is inhib ited by atrial natriuretic peptide (ANP). Inasmuch as alterations in K t conductance can modulate aldosterone secretion, the effect of ANP on intracellular K+ homeostasis was investigated. Intracellular K+ conce ntration ([K+](i)) of AG cells was assessed by spectrofluorometry usin g the K+-sensitive dye, K+-binding benzofuran isophthalate. The restin g 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 aci d-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 mu M (n = 7). In the continued presence of ANP, a rapid recovery to near basal values of [K+](i) was attained within 90 s. Me asurements of membrane voltage using the potential sensitive dye 1-3 t a-(-(di-n-butylamino)-6-naphthyl)vinyl)pyridinium betaine documented a n accompanying change in membrane potential. Pretreatment of AG cells with barium (0.5 mM), tetraethylammonium (0.1 mM), charybdotoxin (100 nM), or ethylene ol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic ac id (0.5 mM) blunted the ANP-induced decrease in [K+](i). ANP-(7-23), t he 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 mu M), 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.