(A) Two-photon microscopy images (maximum intensity projections) of pericytes on first- to third-order capillary branches from the PA in an acute cortical slice of a NG2-Cre^ERT2-GCaMP5G mouse. Dashed white circles denote pericyte somata. Scale bar: 10 μm. (B) Removing extracellular Ca²⁺ abolished the ET-1–evoked [Ca²⁺]_i rise. Time course of GCaMP5G fluorescence (F) in pericyte somata (red trace; n = 32) and processes (other traces; n = 79) normalized to mean baseline fluorescence with 2 mM [Ca²⁺]_o (the last 10 minutes of 15 minutes in 0 [Ca²⁺]_o are shown). [Ca²⁺]_i changes in processes were quantified less than 5 μm from pericyte somata centers (“at soma”) and at 10 μm and 20 μm along the vessel from the soma center. (C) 15 minutes of 0 [Ca²⁺]_o did not affect pericyte [Ca²⁺]_i (compare bottom 2 plots). Reintroducing Ca²⁺ in the continuous presence of ET-1 raised pericyte [Ca²⁺]_i in processes and somata (see also, B). (D) Capillary constriction at pericyte somata (n = 40) coincides with the [Ca²⁺]_i rise upon 2 mM [Ca²⁺]_o reperfusion in B. There was no significant change in capillary diameter away from pericyte somata at 10 μm (n = 18) or 20 μm (n = 11). (E) Capillary diameter is larger at baseline and constricts in response to 2 mM [Ca²⁺]_o reperfusion at pericyte somata. In D and E, diameter is from tdTomato channel. (F) Time course of ET-1–evoked [Ca²⁺]_i change in pericyte somata (n = 23), normalized to aCSF baseline. Nimodipine (3 μM) (n = 27) or vehicle (n = 17) were applied 15 minutes before ET-1 application. (G) Nimodipine greatly attenuated the ET-1–evoked pericyte [Ca²⁺]_i rise (note that 0 [Ca²⁺]_i is at 1 on the y axis) (Kruskal-Wallis test with Dunn’s post hoc test). The inset shows that in the presence of nimodipine, the ET-1–evoked [Ca²⁺]_i rise was similar in pericytes on first-order (n = 9) versus second- and third-order branches (n = 10) (unpaired 2-tailed Student’s t test).