Transepithelial potential measurements in the isolated, perfused head of a marine teleost.

The transepithelial potential (TEP) across the gills of a seawater teleost, the long-horned sculpin (Myoxocephalus octodecimspinosus), was measured both in vivo and utilizing an isolated, perfused head preparation (IPHP). The TEP of the IPHP was compared to that of the whole animal while in normal seawater and Na- or Cl-free seawater. The TEP or the IPHP in seawater was similar to that measured in vivo (+7.7 versus +7.2 mV, respectively). Na-free seawater induced a depolarization of both the IPHP and the intact fish, while Cl-free seawater hyperpolarized the TEP in vivo. The positive TEP of the sculpin, measured both in vivo and in vitro, is indicative of a transbranchial Na+ to Cl- permeability ratio greater than unity. The IPHP of the sculpin exhibits differential ion permeabilities similar to that of the whole animal. TEP comparisons described here should be applied to other IPHP systems now in use.