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Activation of Ca2+ Release from Sarcoplasmic Reticulum Vesicles by 4-Alkylphenols

https://doi.org/10.1006/abbi.1993.1136Get rights and content

Abstract

4-Alkylphenols induce Ca2+ release from junctional (terminal cisternae) sarcoplasmic reticulum vesicles, but not from nonjunctional sarcoplasmic reticulum vesicles. The 4-alkylphenol concentration required to induce Ca2+ release decreases about threefold for every methylene carbon increase in the alkyl chain length, indicating that the Ca2+-releasing potency of 4-alkylphenols is related to their ability to partition into the membrane. The rate and amount of Ca2+ release induced by relatively low 4-octylphenol concentrations (25 nmol/mg protein) are altered by the sarcoplasmic reticulum Ca2+ channel activators, Ca2+ and ATP, and the Ca2+ channel inhibitors, Mg2+ and ruthenium red. Ca2+ release induced by 250 nmol 4-octylphenol/mg protein is much less influenced by Ca2+ channel activators and inhibitors; however, even at this high 4-octylphenol concentration, Ca2+ release is not induced from nonjunctional sarcoplasmic reticulum vesicles. The data indicate that 4-alkylphenols induce Ca2+ release by activating the sarcoplasmic reticulum Ca2+ channel.

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    These new data support a hypothesis in which the 4-CmC binding site most likely resides in close proximity to the lipid bilayer or even at the protein/lipid interface. This hypothesis is supported by studies on structural analogs of 4-CmC such as 4-alkyl phenols whose activity is directly proportional to the length of the 4-alkyl chain (21). These alkyl chains could anchor the compound to the membrane allowing the compound to diffuse to a binding site at the protein/lipid interface of RyR1.

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