title: Cardiac mechanical restitution in active and hibernating Richardson's ground squirrel.
abstract: The cardiac mechanical restitution was compared in papillary muscles between the active and the hibernating Richardson's ground squirrels at 0.1, 2.8, and 5 mM external Ca2+ concentration [( Ca2+]o). The amplitude of the restitution was significantly higher in hibernating animals between 37 and 7 degrees C at all [Ca2+]o. The first postrest contraction (F1) was highest at 20 degrees C and lower at 37 and 7 degrees C in both groups. The pause duration for maximum F1 was 30 s in active but 10 s in hibernating animals at 37 degrees C and increased to 100 s in both groups at 7 degrees C. The postrest potentiation was eliminated by 10(-6) M ryanodine at 20 degrees C in both groups, and this inhibitory effect was more pronounced in the hibernating group. Together, our results suggest that the activator Ca2+ for excitation-contraction coupling is mainly derived from the sarcoplasmic reticulum (SR) pool in both active and hibernating ground squirrel, and the dependence on SR Ca2+ release via ryanodine-sensitive Ca2+ channels is more marked in the hibernating state. Furthermore, there is no significant difference in sensitivity of the cardiac mechanical restitution to [Ca2+]o between the active and the hibernating condition.
authors.affiliation: Department of Biology, Peking University, Beijing, People's Republic of China.
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Zhou
authors.forename: B
authors.initials: B
authors.lastname: Liu
authors.forename: W F
authors.initials: WF
authors.lastname: Dryden
authors.forename: L C
authors.initials: LC
authors.lastname: Wang
mesh_terms: D000204:Activity Cycles; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006605:Hibernation / Q000502:physiology*; D006706:Homeostasis; D009200:Myocardial Contraction; D009994:Osmolar Concentration; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D012589:Sciuridae; D013696:Temperature
chemical_list: D012433:Ryanodine; D002118:Calcium