AJP - Heart and Circulatory Physiology, Vol 259, Issue 5 1601-H1605, Copyright © 1990 by American Physiological Society
Analysis of thermopile records from contracting isolated cardiac muscle
F. Mast, R. C. Woledge and G. Elzinga
Laboratory for Physiology, Free University, Amsterdam, The Netherlands.
Recovery heat production after contraction in rabbit papillary muscle at 20
degrees C occurs at an exponentially declining rate. The time constant
describing this decline is 25 s; it is not different when 10 twitches or
when a steady-state twitch train is studied, and it is unaltered by
changing stimulus frequency from 0.125 to 0.2 Hz. The same value has
previously been found after single twitches. If it is assumed that
phosphocreatine (PCr) resynthesis is the cause of recovery heat production
and that it occurs also during contractions at a rate proportional to the
amount of PCr depletion, it is possible to divide the total heat production
for any period of stimulation into that caused by this recovery process (R)
and that caused by initial (I) processes (presumed to be PCr splitting).
The value of R/I obtained by using this method is 1.10 +/- 0.04 (means +/-
SE, n = 27 muscles), close to the theoretical value of 1.13. The
correspondence between the measured and the predicted ratio supports the
assumptions underlying the measurement. Thus in heart muscle the heat
produced during and after contraction can be explained by PCr splitting and
reformation. The older Bugnard method of analysis applied to the same data
gives an R/I value of 1.5; the reasons for the discrepancy are described.
