Elevated growth hormone increases the Ca2+ sensitivity of slow- and fast-twitch skeletal muscle of female rats.
To determine the effect of plasma growth hormone (GH) on skeletal muscle function, we measured the free Ca2+ concentration-tension relationship of slow-twitch (soleus) and fast-twitch (peroneus longus) muscles isolated from rats undergoing acromegaly in response to implanted, GH-secreting tumors. Muscles from adult (9 mo) and aged rats (24 mo) were studied after the tumor-bearing rats weighted over 50% more than their age-matched controls. Ca(2+)-activated isometric tension was recorded from skinned muscle fibers. For soleus muscles, the free Ca2+ concentration producing 50% of maximal tension ([Ca2+]50) was 2.0 microM for rats with tumors and 3.4-3.6 microM for controls. For peroneus longus fibers, [Ca2+]50 shifted from 6.1-6.7 microM in controls to 3.5 microM after tumors were introduced into either adult or aged rats. Soleus muscle fibers from neonatal rats (14 days) were less sensitive to Ca2+ than those isolated from adult rats, having a [Ca2+]50 of 7.3 microM. The Ca2+ sensitivity of peroneus longus fibers did not change with age. We conclude that significant increases in myofibrillar Ca2+ sensitivity occur in skeletal muscles undergoing rapid growth induced by GH-secreting tumors.
Xu
X
X
Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign 61801, USA.
Forrer
J
J
Bechtel
P J
PJ
Best
P M
PM
D000172:Acromegaly / Q000378:metabolism / Q000503:physiopathology; D000375:Aging / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D009119:Muscle Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism* / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000503:physiopathology; D009994:Osmolar Concentration; D051381:Rats; D011920:Rats, Inbred WF
D013006:Growth Hormone; D002118:Calcium