title: Sarcoplasmic reticulum in cardiac length-dependent activation in rabbits.
abstract: After a step increase in length of rabbit right ventricular papillary muscles, active stress increased immediately followed by a further slow increase in stress over 15-20 min. We studied the contribution of the sarcoplasmic reticulum (SR) to the slow change in stress (SCS) after changing muscle length from 85 to 95% of length at which active force development was maximal. SCS amounted to 32.5 +/- 12.2% mean +/- SD, n = 19) of the total increase in active stress. This was associated with a 13.2 +/- 8.7% increase in calcium content of the SR as estimated with rapid cooling contractures (P < 0.0001, n = 19). However, SCS was not dependent on SR calcium content. There was no significant attenuation in SCS after SR calcium depletion with ryanodine (n = 6), SR Ca(2+)-adenosinetriphosphatase inhibition with cyclopiazonic acid (n = 6), or combined treatment with ryanodine and cyclopiazonic acid (n = 3). We conclude that, in the rabbit, SR calcium content increases slowly after a step increase in cardiac muscle length but the slow changes in active stress are not dependent on the sarcoplasmic reticulum.
authors.affiliation: Department of Bioengineering, University of California, San Diego, La Jolla 92093-0412, USA.
authors.forename: W F
authors.initials: WF
authors.lastname: Bluhm
authors.forename: W Y
authors.initials: WY
authors.lastname: Lew
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000502:physiology; D003080:Cold Temperature; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D010210:Papillary Muscles / Q000502:physiology; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000502:physiology*; D013314:Stress, Mechanical; D016278:Ventricular Function, Right
chemical_list: D007211:Indoles; D012433:Ryanodine; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid; D004121:Dimethyl Sulfoxide