Differential changes in permeability of mesentery to rubidium and phosphate

Abstract

The transfer of Rb⁸⁶ cations and of P³²-orthophosphate anions across isolated rabbit mesentery exhibited kinetic patterns that are usually associated with passive diffusion. Because loading with unlabeled phosphate did not reduce the P³² flux, one infers that no carrier mechanism was operative in this transfer, in accordance with prior conclusions about Rb⁸⁶. An elevation of temperature from 28 to 38 C speeded the transport of both substances, but the effect on the P³² flux was significantly greater (Q₁₀ = 2.1 for P³², 1.6 for Rb⁸⁶). Similarly, the addition of atropine promoted the contemporaneous movements of both tracers, with the P³² flux showing a significantly greater rise. The effect of atropine was blocked by prior treatment of the membrane with acetylcholine, but acetylcholine alone was generally inactive. Histamine and 5-hydroxytryptamine produced a distinctive response; both increased the Rb⁸⁶ flux without affecting the migration of P³². These drug and temperature effects could not be duplicated with cellulose membranes. The results are discussed in relation to pinocytosis and to diffusion through pores as possible modes of transport, but no adequate explanation of mechanisms is yet available.