Transport of Inorganic Ions by Renal Tubules

Abstract

This chapter considers tubular transport of sodium and chloride, potassium, hydrogen ion, calcium, phosphate, magnesium, and sulfate. For each inorganic ion, it examines the direction or directions of transepithelial transport, the tubule sites of transport, and the cellular and molecular mechanisms of transport, so far as they are known in nonmammalian vertebrates. For sodium and chloride, substantial quantitative information on net fluxes is provided. In addition, the electrical properties of the tubule segments measured to date in nonmammalian and mammalian vertebrates are provided and are related particularly to transport of sodium, chloride, and potassium. In so far as possible for each of these inorganic ions, the chapter describes and discusses the cellular and molecular characteristics of the transport steps at both the luminal and peritubular membranes of the renal tubule cells in the various tubule segments. These steps are very poorly defined for the renal tubule cells of many nonmammalian vertebrates, but it is often possible to suggest cellular and molecular processes by analogy with those found in mammals and a few nonmammalian vertebrates and to propose avenues of future research. Finally, the chapter considers hormonal, neural, and other regulatory factors of the transport steps of these inorganic ions, insofar as they are understood in nonmammalian vertebrates.