Experimental and theoretical studies on TI+ interactions with the cation-selective channel of the sarcoplasmic reticulum |
| |
Authors: | James Fox Sergio Ciani |
| |
Institution: | (1) Brain Research Institute (Ahmanson Laboratory of Neurobiology), Department of Physiology, University of California at Los Angeles, 90024 Los Angeles, California;(2) Jerry Lewis Neuromuscular Research Center, University of California at Los Angeles, 90024 Los Angeles, California;(3) Present address: Jules Stein Eye Insitute, U.C.L.A., Los Angeles, USA |
| |
Abstract: | Summary This paper presents an experimental study and a theoretical interpretation of the effects of thallous ion on the electrical properties of the cation-selective channel of the sarcoplasmic reticulum (SR channel). The properties of this channel in solutions which do not contain thallous ion are consistent with the predictions of Läuger's theory for singly occupied pores (P. Läuger, 1973,Biochim. Biophys. Acta
311:423–441). However, this theory does not account for SR channel properties in mixtures containing thallous ion. SR channel conductance is less than predicted in mixed salt solutions of thallium with either potassium or ammonium (J. Fox, 1983,Biochim. Biophys. Acta
736:241–245), yet is greater than expected in mixtures of lithium and thallium. In a simple single-ion pore, the ratio of the products of the single-salt binding constants and maximum conductances is equal to the permeability ratio calculated from zero-current potential experiments under near equilibrium conditions. This is not found for the SR channel when thallous ion is present. SR channel properties in the presence of thallous ion can, however, be explained by a model which postulates the existence of two external modulatory sites on the channel, without implying double-occupancy in the permeation pathway. When thallous ion is bound to a modulatory site the maximum conductance of the channel to all permeating ions is altered (thallous included). Two other models (a three-barrier, two-internal-site pore which allows multiple occupancy, and a pore with fluctuating barriers) are discussed, but are found to be unable to fit our conductance data at different concentrations. |
| |
Keywords: | thallium SR cation channel channel model |
本文献已被 SpringerLink 等数据库收录! |
|