Changes of tension and [Ca2+]i during beta-adrenoceptor activation of single, intact fibres from mouse skeletal muscle.
beta-Adrenergic agonists increase tension production in fast-twitch skeletal muscle, but the underlying mechanism is unknown. In the present study we have exposed intact, single fibres from a mouse muscle to the beta 2-adrenergic agonist terbutaline. Fibres were stimulated to produce 350-ms tetani at 20-100 Hz while measuring the myoplasmic Ca2+ concentration ([Ca2+]i) and tension. The fluorescent indicator Indo-1 was used to measure [Ca2+]i. Application of terbutaline resulted in marked increases of both tetanic [Ca2+]i and tension. Terbutaline had no significant effect on myofibrillar function as judged from normal Ca2+ sensitivity and tension production at saturating [Ca2+]i. The rate of [Ca2+]i and tension decline during relaxation was not affected by terbutaline, thus indicating a normal function of the sarcoplasmic reticulum (SR) Ca2+ pumps. The effect of terbutaline developed gradually over 5-10 min when fibres were stimulated each minute; the full effect of terbutaline was also obtained after a 10-min rest period in terbutaline. The [Ca2+]i at rest was not affected by terbutaline. In conclusion, beta-adrenergic stimulation increases tetanic tension by enhancing SR Ca2+ release.
Cairns
S P
SP
Department of Physiology F13, University of Sydney, NSW, Australia.
Westerblad
H
H
Allen
D G
DG
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000502:physiology; D004558:Electric Stimulation; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology; D013726:Terbutaline / Q000494:pharmacology
D011943:Receptors, Adrenergic, beta; D000252:Calcium-Transporting ATPases; D013726:Terbutaline; D002118:Calcium