title: Effects of ryanodine receptor agonist 4-chloro-m-cresol on myoplasmic free Ca2+ concentration and force of contraction in mouse skeletal muscle.
abstract: In single mouse skeletal muscle fibers injected with fluorescent Ca2+ indicator Indo-1, 4-chloro-m-cresol (chlorocresol, 4-CmC) and its lipophilic analogue 4-chloro-3-ethylphenol (4-CEP) increased resting myoplasmic free [Ca2+] ([Ca2+]i) in a dose-dependent manner. In this regard, 4-CEP was more potent than 4-CmC and both were more potent than caffeine. High concentrations of 4-CmC (1 mM) or 4-CEP (500 microM) caused large and irreversible increase in resting [Ca2+]i leading to contracture. 4-CmC potentiated the [Ca2+]i increase and force of contraction induced by tetanic stimulation. Unlike caffeine, 4-CmC did not affect the activity of sarcoplasmic reticulum Ca2+ pump or the myofibrillar Ca2+ sensitivity. A low concentration of 4-CEP (20 microM) had no effect on resting [Ca2+]i on its own, but it enhanced the resting [Ca2+]i increase induced by caffeine and also potentiated the [Ca2+]i increase and contraction induced by tetanic stimulation. However, a relatively high concentration of 4-CEP (200 microM) inhibited tetanic stimulation-induced [Ca2+]i increase and contraction. Dantrolene, a muscle relaxant, inhibited 4-CmC-induced [Ca2+]i increase under resting conditions. However, when 4-CEP was applied in the presence of dantrolene, there was an exaggerated increase in [Ca2+]i. We conclude that 4-CmC and 4-CEP are potent agonists that can increase [Ca2+]i rapidly and reversibly by activating ryanodine receptors in situ in intact skeletal muscle fibers. These compounds, specially 4-CmC, may be useful for mechanistic and functional studies of ryanodine receptors and excitation-contraction coupling in skeletal muscles.
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institute, Stockholm, Sweden. hakan.westerblad@fyfa.ki.se
authors.forename: H
authors.initials: H
authors.lastname: Westerblad
authors.forename: F H
authors.initials: FH
authors.lastname: Andrade
authors.forename: M S
authors.initials: MS
authors.lastname: Islam
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002733:Chlorophenols / Q000494:pharmacology; D003408:Cresols / Q000494:pharmacology*; D003620:Dantrolene / Q000494:pharmacology; D004558:Electric Stimulation; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism
chemical_list: D002733:Chlorophenols; D003408:Cresols; D019837:Ryanodine Receptor Calcium Release Channel; C091710:4-chloro-3-ethylphenol; C006984:chlorocresol; D002110:Caffeine; D003620:Dantrolene; D002118:Calcium