Correlation between myocardial contractile force and cytosolic
inorganic phosphate during early ischemia.
He, Miao-Xiang, Sheng Wang, and H. Fred Downey.
Department of Integrative Physiology, University of North Texas,
Health Science Center at Fort Worth, Fort Worth, TX 76107
APStracts 3:0484H, 1996.
To test the role of inorganic phosphate (Pi) in downregulation of
myocardial contractile force at the onset of ischemia, Pi of rat
hearts was determined using 31P-NMR spectroscopy. 40 cycles of brief
hypoperfusion (30% of baseline flow for 33 s) were used to achieve a
time resolution of 0.512 s for comparing dynamic changes in Pi and
contractile force. Initial control values of left ventricular
developed pressure (LVP), heart rate, and oxygen consumption were
136+11 mmHg, 236+4 beats/min, and 95+3 [mu]l O2/min/g; these values
were unchanged at the end of the experiment. During the first 10 s of
hypoperfusion, Pi increased at a rate (percentage of the total
observed change) faster than the decrease in LVP; Pi and LVP then
changed at the same rate during the remainder of the hypoperfusion.
ADP did not change in advance of LVP. Intracellular pH did not
change. The results indicate that Pi plays an important role in
initiating the downregulation of myocardial contractile force at the
onset of ischemia. The perfusion pressure decreased rapidly at the
onset of ischemia, which indicated the potential importance of
vascular collapse in the downregulation of myocardial contractile
function during early ischemia. Perfusion pressure also declined
faster than LVP at the onset of ischemia, indicating potential
importance of vascular collapse in contractile downregulation during
early ischemia.
Received 2 July 1996; accepted in final form 15 October 1996.
APS Manuscript Number H586-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996