DIRECT COUPLING BETWEEN BLOOD-FLOW AND METABOLISM AT THE CAPILLARY LEVEL IN STRIATED-MUSCLE

In hamster cremaster muscle, capillary networks consist of anatomicall y 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 micr opipettes to stimulate five to six muscle fibers running underneath sp ecified capillary modules. Capillary erythrocyte flow increased signif icantly at all stimulation frequencies because of increased erythrocyt e content at 2 Hz and increased erythrocyte velocity at 4 and 8 Hz. Er ythrocyte flow did not increase when the fibers underlying the module were mechanically tugged but did not actively contract at these freque ncies. Increased capillary flow was accommodated by dilation of three upstream arteriolar generations: the module inflow arteriole dilated s ignificantly at all frequencies, and further upstream, dilations were significant at higher frequencies. Other module inflow arterioles in t he same capillary network as the stimulated module did not dilate. Dil ations in the module inflow arteriole were abolished by 600 mosM sucro se but were unaffected by 10(-6) M tetrodotoxin. These data suggest th at local coupling between capillary flow and muscle contraction includ es a conducted vasodilation that is responsible for the remote upstrea m dilations.