In:
The Journal of General Physiology, Rockefeller University Press, Vol. 46, No. 5 ( 1963-05-01), p. 851-882
Abstract:
Using frog's sartorius muscles we have found no correlation between phosphocreatine hydrolysis and shortening under conditions (iodoacetate poisoning and anoxia) where this reaction was the only expected source of energy. Phosphocreatine hydrolysis did, however, show a constant term corresponding to the activation heat of A.V. Hill, and a linear term with work. It was concluded that shortening heat comes from some other chemical reaction, or else Hill's equation (E = A + W + ax) fails to describe correctly the energy output in a complete cycle of contraction and relaxation. To decide between these possibilities direct measurements of heat and work during a complete cycle were made. Also, experiments were performed in which heat, work, and phosphocreatine breakdown were measured simultaneously on the same muscles. The total energy output in a complete twitch could be most simply represented by a fixed "activation" heat, plus the work. There was no term corresponding to the shortening heat. Hill's equation must, therefore, be held as invalid for the complete isotonic twitch. A value of 9.8 ± 0.5 (sE) kcal/mole was obtained for the in vivo heat of hydrolysis of phosphocreatine. This quantity showed no significant dependence on load, and it is in good agreement with the value obtained from thermochemical data. It is concluded that phosphocreatine hydrolysis and its associated buffer reactions can account quantitatively for the total energy output of isometric and isotonic twitches.
Type of Medium:
Online Resource
ISSN:
1540-7748
,
0022-1295
DOI:
10.1085/jgp.46.5.851
Language:
English
Publisher:
Rockefeller University Press
Publication Date:
1963
detail.hit.zdb_id:
1477246-2
SSG:
12
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