Some Aspects of Non-ionic Permeation of NH₃ and CO₂ in Mammalian Skeletal Muscle

Abstract

It has been clearly established that NH₃ and CO₂ induce transients of intracellular pH (pH_i) in mammalian skeletal muscle [1] and invertebrate giant nerve fibers [2]. On the other hand, the fact that NH₃ and CO₂ might influence the pH at the surface of the cell (pH_s) has gone largely unrecognized. pH_s can be measured reliably using double-barrelled glass microelectrodes [3]. The aim of the present work was therefore to study the influence of NH₃ and CO₂ on pH_s with this technique and to correlate pH_s and pHj changes. This combined approach provides useful information on the nature and the kinetics of transmembrane permeation of acid-base species [11]. It allows the direct measurement of the pH changes that would be expected in the thin aqueous unstirred layer at the surface of the plasma membrane. It has been shown that diffusion of NH₃ and CO₂ across lipid bilayer membranes should induce, through chemical reactions, H⁺ concentration gradients in the aqueous unstirred layers covering both faces of the bilayer [6,7] and the same should obviously hold for biological membranes. The present work shows this to be the case, at least at the external face of the sarcolemma.