ATRIOPEPTIN STIMULATES CHLORIDE SECRETION IN CULTURED SHARK RECTAL GLAND-CELLS

Monolayer cultures of shark rectal gland (SRG) epithelial cells were treated with atriopeptin (AP), and the effects on Cl- secretion and intracellular guanosine 3',5'-cyclic monophosphate (cGMP) accumulation were examined. Basolateral or apical exposure to 10(-7) M AP markedly stimulated (8-fold) Cl- -dependent, bumetanide-sensitive, short-circuit current (I(sc)). The AP-stimulated I(sc) exhibited transient oscillations before reaching a steady state. This behavior is not observed when I(sc) is activated by other secretagogues such as vasoactive intestinal peptide, 2-chloroadenosine, forskolin, or ionomycin. Intracellular cGMP was concomitantly elevated (10-fold) by 10(-7) M AP. Both I(sc) stimulation and cGMP accumulation responses exhibited a similar dose dependency beginning at an AP concentration of 1 nM. The bilateral response to AP suggests the presence of receptors on both apical and basolateral plasma membranes. These results are the first demonstration of a direct effect of AP on Cl- -secreting epithelial cells. These data also suggest a role for cGMP in mediating Cl- secretion in these cells.