| Abstract: | Changes in the characteristics of activity of sodium, calcium, and potassium channels in the surface membrane during variation of the calcium ion concentration in the extracellular and intracellular medium were investigated by the voltage clamp method during intracellular dialysis of isolated neurons of the mollusksLimnea stagnalis andHelix pomatia. Besides their direct role in passage of the current through the membrane, calcium ions were shown to have two actions, differing in their mechanism, on the functional properties of this membrane. The first was caused by the electrostatic action of calcium ions on the outer surface of the membrane and was manifested as a shift of the potential-dependent characteristics of the ion transport channels along the potential axis; the second is determined by closer interaction of calcium ions with the specific structures of the channels. During the action of calcium-chelating agents EGTA and EDTA on the inner side of the membrane the conductivity of the potassium channels is substantially reduced. With an increase in the intracellular free calcium concentration the conductivity is partially restored. The action of EGTA and EDTA on the outer side of the membrane causes a substantial decrease in the ion selectivity of the calcium channels and changes the kinetics of the portal mechanism. These changes are easily abolished by rinsing off the chelating agents or by returning calcium ions to the external medium. A specific blocking action of an increase in the intracellular free calcium concentration on conductivity of the calcium channels was found.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 69–77, January–February, 1977. |
