Supplementary Figure 8: Surgically removing the capillary tree from its upstream arteriole eliminated arteriolar dilation following capillary stimulation with 10 mM K⁺.

(A) A CaPA preparation with capillaries attached (top) or severed (middle and bottom) with a pipette positioned for capillary (top and middle) or arteriole (bottom) stimulation by pressure ejection. Red arrow indicates the tip of the pipette. Diameter was recorded in Zone 1 (black box) where the primary capillary branches from the arteriole. (B) Arteriolar diameter at Zone 1 in response to 10 mM K⁺ stimulation of attached capillaries (top) or severed capillaries (middle). Application of 10 mM K⁺ to capillaries failed to produce upstream arteriolar dilation after surgical separation of the capillary tree from the arteriole, while direct stimulation of the arteriole with 10 mM K⁺ still led to vasodilation (bottom). This observation confirms the spatial restriction of the pressure ejected solution and indicates that the observed phenomenon relies on inherent conducted signaling from capillaries to the arteriole. (C) Summary data (n = 6 preparations, 6 mice) showing peak diameter changes in Zone 1 in the different configurations: Capillary tree attached (top) or severed (middle and bottom), induced by 10 mM K⁺ applied onto capillaries (top and middle) or the arteriole (bottom). Error bars represent s.e.m.