Tetraphenylboron Increases Choline Permeability through a Calcium Release Channel of Isolated Sarcoplasmic Reticulum

Abstract

The lipophilic anion tetraphenylboron (TPB^-) but not the lipophilic cation tetraphenylphosphonium (TPP⁺) increased the choline permeability of isolated sarcoplasmic reticulum (SR). Choline permeability was mainly measured by the stopped flow method by following the change in scattered light intensity. TPB^- and TPP⁺ did not affect the choline permeabilities of liposomes, liver microsomes, or denatured SR vesicles. These phenomena are similar to the Ca²⁺ release phenomena activated by TPB^- reported by Shoshan, MacLennan, and Wood (J. Biol. Chem. 258, 2837 (1983)). These results strongly suggest that TPB^- activates a pre-existing channel of SR membrane and choline permeates through the same channel as that for the Ca²⁺ release. This channel is different from that for the Ca²⁺-induced Ca²⁺ release. The former is present in all of the vesicles formed by fragmented SR, while the latter is rich in the heavy fraction of fragmented SR and poor in the light fraction. The channel specificities for permeable ions are different from each other. For example, the latter passes Tris⁺ but the former does not. The physiological role of this channel is not clear at present.