Role for capillaries in coupling blood flow with metabolism.

1. Skeletal muscle blood flow is coupled with metabolism; for this coupling to be effective in matching blood flow to capillary exchange, control of capillary blood flow and recruitment must reside at the capillary level. 2. Capillaries are, indeed, capable of sensing and responding to vasoactive stimuli. We report studies that indicate that contraction of skeletal muscle fibres underneath capillaries is capable of increasing blood flow in those capillaries. 3. This presumed metabolically related signal initiates remote dilations in arterioles upstream of the stimulated capillaries. Our findings indicate that the vasodilatory signal is transmitted along the blood vessel wall. 4. Although we present evidence supporting a role for gap junctionally mediated communication of this vasodilatory signal, it appears unlikely to be primarily electrotonic spread of membrane potential changes. 5. Our studies further indicate that the transmitted signal is not dependent on changes in endothelial cell calcium.