Modulation of Ca2+-gated cardiac muscle Ca2+-release channel (ryanodine receptor) by mono- and divalent ions

Publisher Website
Google Scholar
Abstract
The effects of mono- and divalent ions on Ca2+-gated cardiac muscle Ca2+-release channel (ryanodine receptor) activity were examined in [3H]ryanodine-binding measurements. Ca2+bound with the highest apparent affinity to Ca2+activation sites in choline chloride medium, followed by KCl, CsCl, NaCl, and LiCl media. The apparent Ca2+binding affinities of Ca2+inactivation sites were lower in choline chloride and CsCl media than in LiCl, NaCl, and KCl media. Sr2+activated the ryanodine receptor with a lower efficacy than Ca2+. Competition studies indicated that Li+, K+, Mg2+, and Ba2+compete with Ca2+for Ca2+activation sites. In 0.125 M KCl medium, the Ca2+dependence of [3H]ryanodine binding was modified by 5 mM Mg2+and 5 mM β,γ-methyleneadenosine 5′-triphosphate (a nonhydrolyzable ATP analog). The addition of 5 mM glutathione was without appreciable effect. Substitution of Cl−by 2-( N-morpholino)ethanesulfonic acid ion caused an increase in the apparent Ca2+affinity of the Ca2+inactivation sites, whereas an increase in KCl concentration had the opposite effect. These results suggest that cardiac muscle ryanodine receptor activity may be regulated by 1) competitive binding of mono- and divalent cations to Ca2+activation sites, 2) binding of monovalent cations to Ca2+inactivation sites, and 3) binding of anions to anion regulatory sites.