4-chloro-orto-cresol activates ryanodine receptor more selectively and potently than 4-chloro-meta-cresol

Abstract

In this study we performed the comprehensive pharmacological analysis of two stereoisomers of 4-chloro-meta-cresol (4CMC), a popular ryanodine receptor (RyR) agonist used in muscle research. Experiments investigating the Ca²⁺-releasing action of the isomers demonstrated that the most potent isomer was 4-chloro-orto-cresol (4COC) (EC₅₀ = 55 ± 14 μM), although 3-chloro-para-cresol (3CPC) was more effective, as it was able to induce higher magnitude of Ca²⁺ flux from isolated terminal cisterna vesicles. Nevertheless, 3CPC stimulated the hydrolytic activity of the sarcoplasmic reticulum ATP-ase (SERCA) with an EC₅₀ of 91 ± 17 μM, while 4COC affected SERCA only in the millimolar range (IC₅₀ = 1370 ± 88 μM). IC₅₀ of 4CMC for SERCA pump was 167 ± 8 μM, indicating that 4CMC is not a specific RyR agonist either, as it activated RyR in a similar concentration (EC₅₀ = 121 ± 20 μM). Our data suggest that the use of 4COC might be more beneficial than 4CMC in experiments, when Ca²⁺ release should be triggered through RyRs without influencing SERCA activity.

Keywords: 3-chloro-para-cresol; 4-chloro-meta-cresol; Chloro-orto-cresol; Ryanodine receptor; SERCA; Skeletal muscle.