The role of protons in determining membrane electrical characteristics inChara corallina

Summary

The value of the potential difference between the vacuole and the external medium,ψ _vo, and the effects of metabolic inhibitors upon it indicate that, under certain external conditions, there are two main factors determining the potential across the plasmalemma. At all external pH there is a passive diffusion potential and at pH≧6 there is an active electrogenic component of potential. Calculations of ionic permeabilities of K⁺, Na⁺ and Cl⁻ from their respective passive fluxes and application of the Goldman equation indicate that H⁺ permeability is approximately 25 times K⁺ permeability at pH 4 and 5 and possibly at pH≧6.ψ _vo does not respond to increases in [K⁺]₀ when a large electrogenic component of potential is present, even though the calculated value ofP _K under these conditions is such as to predict significant changes inψ _vo. It is suggested that this anomaly may be due to intrinsic properties of the electrogenic pump. There is evidence that the electrogenic pump is an active H⁺ efflux which calculations indicate is about 12 nmoles m⁻² sec⁻¹ at pH 5. However the electrogenic potential does not appear to be related to formation of acid and alkali regions in the external solution adjacent to cells ofChara.