cAMP- and beta-adrenergic-stimulated chloride-dependent Ca2+ secretion in frog skin

This study examined the possible existence and nature of Ca2+ transport in frog skin using 45Ca fluxes and short-circuiting technique. Following the addition to full-thickness frog skin (FTFS) of 8-[p-chlorophenylthio]cAMP (8-CPT-cAMP), forskolin, or 1-methyl-3-isobutylxanthine, the secretory Ca2+ flux increased severalfold, inducing net Ca2+ secretion. The absorptive flux was unchanged. Isoproterenol (10(-6)M) reproduced the effects of cAMP on Ca2+ secretion (-3.76 +/- 0.80 nmol X cm-2 X h-1 vs. +0.04 +/- 0.05 in control) while vasopressin and parathyroid hormone did not alter Ca2+ fluxes. Because FTFS contains subepidermal glands capable of Cl- secretion in response to beta-adrenergic stimulation, split-thickness frog skin (STFS) consisting of the gland-free Na-absorbing surface epithelium was used to localize the anatomic site of Ca2+ secretion. In STFS, addition of 8-CPT-cAMP or isoproterenol failed to induce Ca2+ secretion, suggesting that this transport in FTFS is localized in skin glands. Additional studies explored the relationship between Ca2+ and Cl- transport in FTFS. Furosemide prevented the stimulation of both Ca2+ and Cl- secretion. Removal of Cl- from the bathing medium abolished Ca2+ secretion. Thus, FTFS exhibits a beta-adrenergic, cAMP-stimulated net Ca2+ secretion that is Cl- dependent. As this effect is not observed in STFS, the pathway of Ca2+ secretion in frog skin is probably localized in the subepidermal glandular epithelium in association with Cl- secretion. Frog skin glands may represent a useful model for the study of Ca2+ transport in Cl--transporting epithelia.