Depolarization in high external K+ causes CBF excitation. Depolarization in high external K+ causes CBF excitation. (A) 30 mmol l-1 K+ bath (filled circles) significantly increases CBF as compared to ASW controls (N=5, P≤0.0003) in CPE cell explants. After 3 min, 30 mmol l-1 K+ is still excitatory (P≤0.02) but less so. After 6 min, 30 mmol l-1 K+ is no longer excitatory. 30 mmol l-1 K+ seawater was not excitatory in a zero Ca2+ bath (open squares, N=6), and only transiently so (P≤0.02) in a bath containing 50 μmol l-1 of the Ca2+ channel blocker nifedipine (triangles, N=5). (B) 30 mmol l-1 K+ significantly excites CBF in isolated, individual CPE cells (N=5, P≤0.007). *Significant change from mean basal levels. Owen M. Woodward, and A. O. Dennis Willows J Exp Biol 2006;209:2765-2773 © The Company of Biologists Limited 2006