The effects of hydrogen ions on the resting membrane potential of frog sartorius muscle.

Abstract

A considerable amount of work has been done on the study of the effect of H+ ion on the resting membrane potential of frog skeletal muscle fibres and other kinds of tissue as well. The observations, however, are rather contradictory. This may be due to differences in membrane properties of these tissues. The conditions under which the experiments were carried out might also have important effects on the responses as shown in the present paper. The present study has been carried out in order to establish the effects of H+ ions on the resting membrane potential of frog sartorius muscle fibres and to investigate the mechanism by which H+ ions exert their effects. The results show that in frog sartorius muscle under relatively normal conditions, i.e. in Ringer's solution (Table II), the short term effect of lowering pH was to increase the resting membrane potential, while that of raising pH, to reduce the potential. Under these conditions the change in resting membrane potential is small, usually about 1-4 mV. Accompanying the change in resting potential is an equally rapid and reversible change in membrane resistance. Thus, the membrane resistance increases as pH falls. Consideration of the equivalent circuit of cell membrane suggests that the changes in resting membrane potential may result from membrane resistance changes. Since the responses to changes in pH persisted even in the absence of Na+ the study could be focused on the relative effects of H+ on K+ resistance and Cl- resistance of the membrane. When the relationship between the electrochemical potentials of the ions inside and outside of the cell is changed, the response to pH could provide some clues in the estimation of the relative effects of H+ ions on the component resistances of the cell membrane. It has been observed that in muscle fibre with the relation: ECl > Em > E K, lowering pH decreased the resting membrane potential. This would occur if H+ reduced the Cl- conductance of the membrane, or it decreased Cl- conductance to a greater extent than K+ conductance. The interpretation can be fitted into the response of normal cell with the relation: EK > Em > ECl, since with a higher Cl- resistance in acid the influence of ECl on Em would decrease. In each case there is a shift of Em toward EK. A theoretical consideration using the known interrelation between membrane potential, intracellular Cl- concentration and the flux of Cl- and K+ together with the measured increase in the membrane resistance in lowering the pH confirms that H + acts chiefly on Cl- resistance of the membrane in frog sartorius muscle. The physiological significance of the response with change in membrane potential to altering extracellular pH is unknown.