Abstract
It has been known that atrial natriuretic peptide (ANP) inhibits Na+ reabsorption in renal tubules of the mammalian kidney. We, however, recently reported that ANP and cGMP stimulate amiloride-blockable Na+ absorption through PKA-dependent pathway in the urinary bladder of the Japanese tree frog, Hyla japonica. We also suggested that there is a possibility of expression of cyclic nucleotide-gated channels in the frog urinary bladder using Ussing chamber voltage-clamp and whole cell patch-clamp techniques (Yamada et al., 2005). In the present study, we examined to identify characteristics of the channels activated with ANP and cGMP by using a single channel recording in epithelial cells of urinary bladder. In the recordings of cell-attached patch with NaCl in a patch pipette, a variety of ion channels were revealed the activity with conductance ranging from 5 to 30 pS. Ion channels with conductance for inward current of 5-7 pS were examined because the channels have the same properties, such as conductance and slow opening and closing kinetics with the epithelial Na channels in the toad urinary bladder. When Cl− in the pipette solution was replaced by gluconate, the conductance of the channel did not change. This shows the channel carries cations but anions. Addition of 10−4 M 8-Br-cGMP to the bath solution significantly stimulated the inward current in the cell-attached patches. These results suggest that ANP- and cGMP-dependent increases in Na+ absorption are mediated by 5-7 pS cation channels in the epitherlial cells of the frog urinary bladder. [J Physiol Sci. 2006;56 Suppl:S141]
