Potassium secretion by nasal salt glands of desert lizard Sauromalus obesus

Potassium secretion by the nasal salt glands of the herbivorous desert lizard Sauromalus obesus was determined in vivo by a new technique. Intraperitoneal injection of KCl rapidly increased the potassium secretion rate from 0.28 to 15.35 μmol·100g^-1·h^-1. A second identical intraperitoneal injection, given 15 h after the first, further increased potassium secretion to 50.09 μmol·100 g^-1·h^-1. This was associated with a doubling of plasma K⁺ concentration and salt gland Na⁺-K⁺-adenosinetriphosphatase (ATPase) activity. Neither salt gland weight or residual (Mg²⁺) ATPase activity were affected. In an isolated perfused head preparation, potassium secretion from the nosal salt glands was stimulated from 0.99 to 10.76 μmol·100 g^-1·h^-1 by methacholine and to 14.68 μmol·100 g^-1·h^-1 by forskolin. In this perfused preparation, simultaneous determination of salt gland perfusion flow (using radiolabeled microspheres) and the rate of potassium secretion revealed that the secreting glands removed 68% of the perfusing potassium ions. Calculations indicated that secretion at the maximal rate observed in vivo would necessitate a fourfold increase in the rate of blood flow to the gland.