Effects of sprint training on contractility and [Ca(2+)](i) transients in adult rat myocytes.
The effects of 6-8 wk of high-intensity sprint training (HIST) on rat myocyte contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) transients were investigated. Compared with sedentary (Sed) myocytes, HIST induced a modest (5%) but significant (P < 0.0005) increase in cell length with no changes in cell width. In addition, the percentage of myosin heavy chain alpha-isoenzyme increased significantly (P < 0.02) from 0.566 +/- 0.077% in Sed rats to 0.871 +/- 0.006% in HIST rats. At all three (0.6, 1.8, and 5 mM) extracellular Ca(2+) concentrations ([Ca(2+)](o)) examined, maximal shortening amplitudes and maximal shortening velocities were significantly (P < 0.0001) lower and half-times of relaxation were significantly (P < 0.005) longer in HIST myocytes. HIST myocytes had significantly (P < 0.0001) higher diastolic [Ca(2+)](i) levels. Compared with Sed myocytes, systolic [Ca(2+)](i) levels in HIST myocytes were higher at 0.6 mM [Ca(2+)](o), similar at 1.8 mM [Ca(2+)](o), and lower at 5 mM [Ca(2+)](o). The amplitudes of [Ca(2+)](i) transients were significantly (P < 0.0001) lower in HIST myocytes. Half-times of [Ca(2+)](i) transient decline, an estimate of sarcoplasmic reticulum (SR) Ca(2+) uptake activity, were not different between Sed and HIST myocytes. Compared with Sed hearts, Western blots demonstrated a significant (P < 0.03) threefold decrease in Na(+)/Ca(2+) exchanger, but SR Ca(2+)-ATPase and calsequestrin protein levels were unchanged in HIST hearts. We conclude that HIST effected diminished myocyte contractile function and [Ca(2+)](i) transient amplitudes under the conditions studied. We speculate that downregulation of Na(+)/Ca(2+) exchanger may partly account for the decreased contractility in HIST myocytes.
Zhang
Xue-Qian
XQ
Weis Center for Research, Geisinger Medical Center, Danville, Pennsylvania 17822, USA.
Song
Jianliang
J
Carl
Lois L
LL
Shi
Weixing
W
Qureshi
Anwer
A
Tian
Qiang
Q
Cheung
Joseph Y
JY
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002155:Calsequestrin / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D009218:Myosins / Q000378:metabolism; D009994:Osmolar Concentration; D010805:Physical Conditioning, Animal; D010807:Physical Endurance / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D014018:Tissue Distribution
D002155:Calsequestrin; D007527:Isoenzymes; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D009218:Myosins; D000252:Calcium-Transporting ATPases; D002118:Calcium