Reciprocal control of the conformational state of the sarcoplasmic reticulum calcium channel protein by polarization and depolarization in the transverse tubule

Abstract

We attached the conformational probe methylcoumarin acetate (MCA) specifically to the junctional foot protein (JFP) moiety of triads, and monitored conformational changes in the JFP during polarization and depolarization of the T-tubule moiety. The MCA fluorescence decreased upon T-tubule polarization, and the fluorescence changes were blocked by preventing T-tubule polarization or by a nimodipine block of the T-tubule-to-sarcoplasmic reticulum communication. Depolarization of the T-tubule reversed the MCA fluorescence decrease which had been produced by T-tubule polarization. These results suggest that the conformational and functional states of the JFP are regulated by T-tubule polarization and depolarization in a reciprocal fashion.