Role of circulation in maintaining Na+ and K+ concentration in pelvic patch in Rana catesbeiana

R. H. Parsons and R. Schwartz Department of Biology and Biophysics Center, Rensselaer Polytechnic Institute, Troy, New York 12180-3590. Skin samples from the pelvic, pectoral, and back areas of frogs were taken from control (C) animals and from dehydrated animals under three conditions: dehydrated and not exposed to a bathing medium (D), dehydrated live and ventral surface exposed to a bathing medium (DL), and dehydrated with heart stopped and ventral surface exposed to a bathing medium (DHS). The skin concentration of Na+ and K+ of the pelvic patch in the absence of circulation was significantly reduced [DHS 286 +/- 22 microM/mg dry wt (n = 6)] compared with control [C 392 +/- 21 microM/mg dry wt (n = 8)]. However, the pelvic skin concentration was maintained in a frog with an intact circulation [DL 381 +/- 26 microM/mg dry wt (n = 7)] even in the presence of a high pelvic water flow [684 +/- 105 cm3.cm-2.s-1.10(-7) (n = 13)]. The water uptake in the pectoral region [231 +/- 54 cm3.cm-2.s-1.10(-7) (n = 13)] was not high enough to predict a dilution, and none was found. The concentrations were 354 +/- 21 (n = 8), 359 +/- 22 (n = 7), 353 +/- 26 (n = 7), and 373 +/- 45 microM/mg dry wt (n = 6) for C, D, DL, and DHS, respectively. Examination of the Na+ and K+ concentrations separately in the pelvic skin shows that the lower salt content in DHS frogs is mainly due to a loss of Na+.