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J Appl Physiol (January 18, 2002). doi:10.1152/japplphysiol.00735.2001
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Articles in PresS, published online ahead of print January 18, 2002
J Appl Physiol, 10.1152/jap.00735.2001
Submitted on July 17, 2001
Accepted on January 11, 2002

DYNAMICS OF MICROVASCULAR OXYGEN PRESSURE IN THE RAT DIAPHRAGM

Crystal M Geer1, Brad J Behnke1, Paul McDonough1, and David C Poole1*

1 Departments of Kinesiology, Anatomy and Physiology, Kansas State University, Manhattan, KS, USA

* To whom correspondence should be addressed. E-mail: poole{at}vet.ksu.edu.

The relative amplitudes and the rate of increase of the muscle blood flow (and O2 delivery, QO2) and O2 uptake (VO2) responses determine the O2 pressure within the muscle microvasculature (PO2m) across the rest to contractions transition. Skeletal muscle function is a primary determinant of pulmonary VO2 kinetics, however, it has never been determined whether the dynamics of muscle PO2m are faster in a highly oxidative muscle (e.g., diaphragm, citrate synthase activity, 39 µm/min/g) as compared with less oxidative muscles (e.g., spinotrapezius, citrate synthase activity, 14 µm/min/g, male Sprague-Dawley rats, ref. 8). Phosphorescence quenching techniques (porphyrin dendrimer, R2) were used to determine PO2m across the transition to electrically-stimulated contractions (1 Hz) within the rat diaphragm (Dia). Following a delay of 10.4±1.3 s (mean±SE) at the beginning of Dia contractions, PO2m decreased close to monoexponentially from 42±2 to 27±3 mmHg (P<0.05) with an extremely fast time constant ({tau}) of 7.1±1.1 s. Thus, Dia PO2m decreased with significantly (P<0.05) faster kinetics than reported previously for the spinotrapezius (Spino) muscle (delay, 19.2±2.8 s; {tau} PO2m, 21.7±2.1 s, ref. 4). Using two specialized muscles with similar fiber type composition but widely disparate oxidative capacities (8), these data demonstrate that PO2m kinetics are significantly faster in the highly oxidative Dia compared to the low oxidative Spino muscle and that this effect is not dependent on muscle fiber type composition.




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