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.