Atrial natriuretic peptide and cGMP activate sodium transport through PKA-dependent pathway in the urinary bladder of the Japanese tree frog.

The effects of atrial natriuretic peptide (ANP) and cGMP on transepithelial ion transport were examined in the urinary bladder of the Japanese tree frog, Hyla japonica, using Ussing chamber voltage-clamp and whole-cell patch-clamp techniques. When the bladders were exposed to 4.4 x 10(-11) to 10(-6) M ANP or 10(-7) to 3 x 10(-4) M 8-Br-cGMP, both the transepithelial potential difference (PD) and the short-circuit current (Isc) were significantly increased in a concentration-response manner. The cGMP-dependent responses were inhibited in a Na+-free bath solution and in the presence of amiloride. The cGMP-dependent increases in Isc were significantly inhibited by specific PKA inhibitors (5 x 10(-7) M KT-5720 and >10(-5) M H-89), but not by a specific PKG inhibitor (5 x 10(-7) M KT-5823). ANP-dependent increases in Isc were also significantly inhibited by KT-5720. In the patch-clamp study, ANP and cGMP significantly increased in inward currents involving Na+ uptake. These results suggest that a cross-talk mechanism exists between cAMP and cGMP signaling pathways, which leads to Na+ transport in the frog urinary bladder. In addition, the cGMP-dependent increases in Isc were partially inhibited by 10(-4) M l-cis-diltiazem, a specific inhibitor of cyclic nucleotide-gated (CNG) channels. These results also suggest a relation between CNG channels and the cGMP-dependent increases in Na+ absorption of the frog urinary bladder.