Deletion of amino acids 1641-2437 from the foot region of skeletal muscle ryanodine receptor alters the conduction properties of the Ca release channel

Abstract

The ryanodine receptor (RyR) of skeletal muscle contains two functional domains: a carboxyl-terminal hydrophobic domain that forms the putative conduction pore of the calcium release channel, and a large cytoplasmic domain that corresponds to the "foot structure." To understand the contribution of the foot structure to the function of the calcium release channel, we studied a RyR deletion mutant, delta(1641-2437)-RyR, in which a region that is rich in glutamate and aspartate residues (a.a. 1641-2437) was removed. The wild-type and delta(1641-2437)-RyR proteins were expressed in a Chinese hamster ovary (CHO) cell line, and functions of single calcium release channels were measured in the lipid bilayer membrane. The wild-type RyR forms functional calcium release channels with a linear current-voltage relationship similar to that of the native channel identified in the sarcoplasmic reticulum membrane of skeletal muscle, whereas the channels formed by delta(1641-2437)-RyR exhibit significant inward rectification, i.e., currents moving from cytoplasm into SR lumen were approximately 20% less than that in the opposite direction. As in to the wt-RyR channel, opening of the delta(1641-2437)-RyR channel has a bell-shaped dependence on the cytoplasmic calcium, but the calcium-dependent activation and inactivation processes of the delta(1641-2437)-RyR channel are shifted to higher calcium concentrations. Our data show that deletion of a.a. 1641-2437 from the foot region of the skeletal muscle RyR results in changes in both ion conduction and calcium-dependent regulation of the calcium release channel.