Direct coupling between blood flow and metabolism at the capillary level in striated muscle.

In hamster cremaster muscle, capillary networks consist of anatomically invariant subunits termed modules [Berg, B. R., and I. H. Sarelius, Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H1215-H1222, 1995]. To explore local coupling between blood flow and metabolism, we used micropipettes to stimulate five to six muscle fibers running underneath specified capillary modules. Capillary erythrocyte flow increased significantly at all stimulation frequencies because of increased erythrocyte content at 2 Hz and increased erythrocyte velocity at 4 and 8 Hz. Erythrocyte flow did not increase when the fibers underlying the module were mechanically tugged but did not actively contract at these frequencies. Increased capillary flow was accommodated by dilation of three upstream arteriolar generations: the module inflow arteriole dilated significantly at all frequencies, and further upstream, dilations were significant at higher frequencies. Other module inflow arterioles in the same capillary network as the stimulated module did not dilate. Dilations in the module inflow arteriole were abolished by 600 mosM sucrose but were unaffected by 10(-6) M tetrodotoxin. These data suggest that local coupling between capillary flow and muscle contraction includes a conducted vasodilation that is responsible for the remote upstream dilations.