Rate of heat production related to degree of filament overlap in chick ALD muscle

Abstract

The anterior latissimus dorsi (ALD) of chicks (2 wk old) was examined for rate of heat liberation when the muscle was reversibly stretched from L0 to about 1.6 L0. The "plateau" forces of isometric tetani were related to the corresponding rates of heat liberation. Presumably, in this region of length change the degree of overlap between the thick and thin filaments is changing. If the amount of overlap is known, the number of heavy meromyosin cross bridges in activity can be estimated. From this information, the amount of liberated energy can be calculated for a single cross-bridge cycling. In all of our measurements, there was heat production even at muscle lengths so great that no filament overlap would have to be assumed. This finding was incorported into the estimate for energy release per cross-bridge cycling.

Variation in the isometric maintenance heat rate with muscle length near that of maximum tension in frog striated muscle.

“…Others have found that the P = 0 intercept of heat versus tension is a substantial fraction of the total maintenance heat in experiments where the full range of tension was examined (e.g. Smith, 1972, on striated muscle from Rana temporaria and Bufo bufo, and Matsumoto & McPhedran, 1977, on chick striated muscle).…”