Abstract:
PURPOSE AND METHODS:The isovolumic contractile responsiveness of left ventricular (LV) myocardium to altered extracellular [Ca2+], [Na+], and pacing frequency was examined using perfused hearts (37 degrees C) isolated from sedentary (SED) and treadmill-trained (TR) adult female rats. RESULTS:The suppressive effect of reducing perfusate free [Ca2+] to 0.7 mM on LV developed pressure (delta LVP) was greater in the TR hearts compared with SED hearts (P < 0.05). When perfusate [Na+] was reduced to 120 mM ([Ca2+] = 0.7 mM), delta LVP augmentation was greatest in the TR hearts (P < 0.05). The negative force-frequency relationship observed at physiologic [Ca2+] and [Na+] was progressively altered toward a positive force-frequency relationship with each subsequent change in perfusate [Ca2+] and [Na+] although the effect was greatest in TR hearts (P < 0.05). CONCLUSIONS:Training elicited a small but significant (P < 0.05) prolongation in the pressure development phase of contraction. Under the physiological [Ca2+], [Na+] perfusion condition, training produced an increase in the magnitude of extrasystolic potentiation of LV pressure, whereas the time constant of mechanical restitution was unaffected. Training affected neither the Ca(2+)-dependence nor the maximal capacity of [3H] ryanodine binding to LV myocardial homogenates. The simplest interpretation of [Na+] and [Ca2+] reduction experiments is that myocardial Ca2+ efflux was augmented by exercise training.
journal_name
Med Sci Sports Exercjournal_title
Medicine and science in sports and exerciseauthors
Lankford EB,Korzick DH,Palmer BM,Stauffer BL,Cheung JY,Moore RLdoi
10.1097/00005768-199810000-00006subject
Has Abstractpub_date
1998-10-01 00:00:00pages
1502-9issue
10eissn
0195-9131issn
1530-0315journal_volume
30pub_type
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journal_title:Medicine and science in sports and exercise
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