Permeation of Neutral Molecules through Calcium Channel in Sarcoplasmic Reticulum Vesicles

Abstract

Permeation of neutral molecules as well as Ca²⁺ through the Ca²⁺ channel in sarcoplasmic reticulum vesicles has been studied by the tracer and/or by the light scattering methods. In the absence of KCl, the Ca²⁺ channel was found not to be able to pass neutral molecules such as glucose, xylose, and glycine under the condition that the channel was open, although the channel could pass Ca²⁺. On the other hand, submolar concentrations of KCl made the channel become permeable to neutral molecules as well as Ca²⁺. Since the effect of KCl could be replaced by NaCl and KNO₃, but not by sucrose and glucose, this effect of KCl is considered to be due to ionic strength and not to osmotic pressure. These results suggest that low ionic strength transforms the Ca²⁺ channel protein in such a manner as to block the permeation of neutral molecules without modifying the gating mechanism of the channel.