I am trying to measure the second order mesenteric artery internal diameter at different intraluminal pressures of 60 to 160 mm Hg under HEPES [mmol/L(140 NaCl, 5 KC1, 1.2 MgSO4, 2.0 CaC12, 10 sodium acetate, 10 N-2-hydroxyethylpiperazine-N0-2-ethanesulfonic acid, 1.2 Na2H2PO4, 5 glucose) and Ca2+ free HEPES+3mmol EDTA + 15mmol KCN. At each pressure, we let the vessel reach a steady diameter for 8 min, and then go for the next pressure step.

I am calculating the myogenic tone at each pressure using formula:

(DiaCA2+ FREE−DiaHEPES)/DiaCa2+ free]×100,

I cann’t find proper passive dilation with Ca2+ free HEPES, anyone else faced the similar problem ? How did you resolve it?

I incubate the vessel with Ca2+ free HEPES for 1 h. I have tried incubating the vessel at 20mm throughout the Ca2+ free HEPES treatment and then increase the pressure to 60mm for further recording, still I don't see a appreciable difference.