title: Halothane does not alter Ca2+ affinity of troponin C.
abstract: Troponin C has been suggested as a possible target for the negative inotropic action of volatile anesthetics. This study has examined the effect of halothane on the structure and response of isolated cardiac troponin C to Ca2+ and the response of skinned soleus and cardiac muscle fibers to Ca2+. The high-affinity Ca(2+)-binding sites of cardiac troponin C were assessed by measurement of the change in intrinsic tyrosine fluorescence and ultraviolet circular dichroism in response to Ca2+ in the presence and absence of halothane. Halothane (0.9 mM, 1.4%) did not alter the 45% enhancement in intrinsic tyrosine fluorescence that occurs with saturation of the high-affinity sites or change the Ca2+ concentration at which half-maximal enhancement occurred. The molar ellipticity in the far ultraviolet region, a measure of the secondary structure, increased to a similar extent with addition of 10(-6) M Ca2+ in the absence and presence of 1.0 mM (1.6%) halothane. The binding rate of the sulfhydryl reagent, 5,5'-dithiobis (2-nitrobenzoic acid), to troponin C in response to Ca2+ titration was used as a measure of the integrity of the low-affinity Ca(2+)-binding site in troponin C in the presence and absence of 1.0 mM (1.6%) halothane. The rate of reaction was stimulated twofold, and the half maximal effect was observed at pCa 4.8 +/- 0.2 in both control and halothane-treated samples. Halothane (5 mM; 7.8%) did not change the pCa/tension response of skinned soleus fibers; the data were fit to the Hill equation and yielded dissociation constants of 6.2 x 10(-7) M for control and halothane-treated specimens.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland.
authors.forename: T J
authors.initials: TJ
authors.lastname: Blanck
authors.forename: E
authors.initials: E
authors.lastname: Chiancone
authors.forename: G
authors.initials: G
authors.lastname: Salviati
authors.forename: E S
authors.initials: ES
authors.lastname: Heitmiller
authors.forename: D
authors.initials: D
authors.lastname: Verzili
authors.forename: G
authors.initials: G
authors.lastname: Luciani
authors.forename: G
authors.initials: G
authors.lastname: Colotti
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D006221:Halothane / Q000494:pharmacology*; D008297:Male; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D014336:Troponin / Q000378:metabolism*; D019209:Troponin C
chemical_list: D014336:Troponin; D019209:Troponin C; D002118:Calcium; D006221:Halothane