Significance of Membrane Calcium in Calcium-free and Potassium-rich Media

Abstract

FROG Ranvier's nodes immersed in potassium-rich media are capable of producing action potentials when the membrane is hyperpolarized by anodal currents¹. This observation was confirmed in frog sartorius muscles by one of us, who found that action potentials were restored by anodal polarization in frog sartorius muscles which depolarized in calcium-free media². The so-called ‘hyper-polarizing response’ was also observed in muscle fibres soaked in both potassium-rich and calcium-free media. This experimental evidence seems to suggest that removal of calcium from the membrane in these two solutions might be responsible for the loss of membrane excitability, as suggested in a previous communication². The rate of output of calcium-45 loaded on muscles, therefore, was studied in both calcium-free and potassium-rich solutions.