Evidence for active chloride transport in dogfish rectal gland

To evaluate the characteristics of the transport process for Na and C1 by the rectal gland of the dogfish shark, experiments were performed with an in vitro perfused model. Changes in glandular secretion rate and net electrical potential difference (PD) were measured during independent alterations of the Na and C1 concentrations of the perfusate solution. The rate of net secretion was enhanced by increasing the concentration of either Na or Cl in the perfusate, demonstrating a substratedependent process. When tetramethyl-ammonium was substituted for Na, the rate of secretion fell in association with a rise in net PD from -8 mV to -17 mV (lumen negative). When SO4 was substituted for Cl, secretion rate also fell, but in association with a fall in net PD. Despite almost complete replacement of Cl with SO4, net PD was not reversed. Although the mechanism responsible for Na secretion remains unclear, these data suggest that chloride is transported by an active process in the dogfish rectal gland.