Calcium and potassium currents of the membrane of a barnacle muscle fibre in relation to the calcium spike

1. The behaviour of membrane currents in a giant muscle fibre of a certain barnacle Balanus nubilus, Darwin, was studied by using voltage clamp technique after treating fibres with a Ca-chelating internal solution.2. Membrane currents can be classified into an early transient current and a late outward current.3. The early transient current can be considered a sum of an inward and an outward component of different properties.4. A conditioning depolarization suppresses the inward component but not the outward component.5. Procaine suppresses the outward component and Co ions suppress the inward component.6. Changes in the external Ca ion concentration alter the inward component but not the outward component.7. The inward component is considered to be carried by Ca ions and the outward component mainly by K ions.8. The outward component of the early current is similar to the current expected from the resting membrane conductance.9. It is concluded that the early conductance increase of the barnacle muscle fibre membrane occurs only to Ca ions but not to K ions, although the membrane potential at the peak of spike is determined by both ions.

Effect of external and internal pH changes on K and Cl conductances in the muscle fiber membrane of a giant barnacle

The membrane potential and conductance of the giant muscle fiber of a barnacle (Balanus nubilus Darwin) were analyzed in relation to changes in the external (3.5-10.0) and the internal (4.7-9.6) pH, under various experimental conditions. A sharp increase in membrane conductance, associated with a large increase in conductance to Cl ions, was observed when the external pH was lowered to values below 5.0. The ratio of Cl to K conductance in normal barnacle saline is between (1/6)-1/7 at pH 7.7, whereas at pH 4.0 the ratio is about 6-9. The behavior of the membrane in response to pH changes in a Cl-depleted muscle fiber shows that the K conductance decreases with decreasing external pH for the whole range of pH examined. A steep increase in Cl conductance is also observed when the internal pH of the fiber is lowered below 5.0. The K to Cl conductance ratio increases with increasing internal pH in a manner very similar to that found when the external pH is raised above 5.0. These facts suggest that the membrane is amphoteric with positive and negative fixed charge groups having dissociation constants such that at pH greater than 5, negative groups predominate and cations permeate more easily than anions, while at lower pH positive groups predominate, facilitating the passage of anions through the membrane.