AJP - Cell Physiology, Vol 256, Issue 4 C719-C727, Copyright © 1989 by American Physiological Society
Effects of substrate and hypoxia on smooth muscle metabolism and contraction
I. R. Wendt
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Suprabasal heat production, oxygen consumption, and lactate production were
measured, together with force, in 30-s isometric contractions of
longitudinal smooth muscle from rabbit urinary bladder at 27 degrees C.
Either glucose or pyruvate was provided as exogenous substrate. Under
aerobic conditions with glucose as substrate, force averaged 95 mN/mm2 and
heat production 121 mJ/g. Oxygen consumption (0.18 mumol/g) could account
for only two-thirds of the total energy expenditure represented as heat
production. The remaining one-third was accounted for by aerobic lactate
production (0.36 mumol/g). When pyruvate replaced glucose as substrate,
both the force developed and the total heat liberated were unchanged.
Oxygen consumption, however, increased by approximately 40% (to 0.25
mumol/g) and was able to fully account for the measured heat production.
The frequency of spontaneous contractions under aerobic conditions was
always reduced in the presence of pyruvate. Under anaerobic conditions
force was essentially unaltered, and heat production was only slightly
reduced (101 mJ/g) with glucose present. Lactate production increased
threefold over that under aerobic conditions. With pyruvate as substrate
both force and heat production declined markedly (to less than 5% of the
aerobic values). The results indicate that under aerobic conditions and
with glucose as substrate, smooth muscle of rabbit urinary bladder
generates about one-third of its suprabasal energy requirements through
glycolysis and that glycolysis can be further accelerated under anaerobic
conditions to provide sufficient energy to sustain contraction. If pyruvate
replaces glucose as substrate, the metabolism shifts to being virtually all
oxidative, and contraction can no longer be sustained in the absence of
oxygen.
