Parvalbumin relaxes frog skeletal muscle when sarcoplasmic reticulum Ca(2+)-ATPase is inhibited.
Inhibition of sarcoplasmic reticulum (SR) Ca(2+)-adenosinetriphosphatase (ATPase) with 2,5-di-(tert-butyl)-1,4-benzohydroquinone (TBQ) in frog skeletal muscle fibers at 10 degrees C prolonged the half time of the fall of the Ca2+ transient by 62% and twitch force by 100% and increased peak force by 120% without increasing the amplitude of the Ca2+ signal. In the presence of TBQ the rate of relaxation and the rate of fall of Ca2+ became progressively slower in a series of twitches until relaxation failed. Relaxation rate decreased with a time course (approximately 2 s-1) similar to the Mg2+ off rate from purified parvalbumin (PA; 3.6 s-1). TBQ slowed the rate of fall of Ca2+ (5-fold) and force (8-fold) in a 0.3-s tetanus so that the rate of fall of Ca2+ (approximately 2.5 s-1) was similar to the Mg2+ off rate from PA. TBQ caused a near total failure of both Ca2+ sequestration and relaxation in a 1.1-s tetanus, during which PA would be saturated with Ca2+ and could not contribute to relaxation. Thus, when the SR Ca(2+)-ATPase is inhibited, Mg(2+)-PA can sequester Ca2+ and produce relaxation at a rate that is defined by the Mg2+ off rate from PA.
Jiang
Y
Y
Department of Physiology, Ohio State University, Columbus 43210, USA.
Johnson
J D
JD
Rall
J A
JA
D000814:Aniline Compounds; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D007537:Isometric Contraction; D009126:Muscle Relaxation; D018482:Muscle, Skeletal / Q000187:drug effects*; D010320:Parvalbumins / Q000494:pharmacology*; D011896:Rana temporaria; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014966:Xanthenes
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D010320:Parvalbumins; D014966:Xanthenes; C058776:2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic acid; C059715:Fluo-3; D000252:Calcium-Transporting ATPases; D016257:Fura-2