AJP - Cell Physiology, Vol 252, Issue 1 C88-C96, Copyright © 1987 by American Physiological Society
Energy expenditure of longitudinal smooth muscle of rabbit urinary bladder
I. R. Wendt and C. L. Gibbs
Heat production, oxygen consumption, and lactate production of longitudinal
smooth muscle from rabbit urinary bladder has been measured at 27 degrees
C. In isometric contractions (initiated by 1-Hz electrical stimulation)
ranging in duration from 2 to 300 s, total energy expenditure correlated
linearly with the force-time integral. For any given force-time integral
oxygen consumption could account for only approximately 60% of the total
energy measured as heat production. A substantial contribution of aerobic
lactate production to the total energy flux was observed. This lactate
production was also linearly correlated with force-time integral and was of
sufficient magnitude to account for the discrepancy between total energy
expenditure determined as heat production and oxygen consumption. The
suprabasal rate of energy expenditure during the maintenance of force was
approximately 2.6 mW/g and remained constant throughout contractions of up
to 5-min duration, suggesting that in this muscle there is no change in the
energetic cost of force maintenance with increasing duration of
contraction. The rate of energy expenditure during the initial period of
force development was, however, about twofold greater than that during
subsequent force maintenance, indicating that there is an extra energy cost
associated with the activation of contraction and development of force
above that required for force maintenance.
