Cells were resuspended in HEPES buffer containing the following (in mm): 136 NaCl, 5.6 KCl, 1 MgCl2, 2.2 CaCl2, 11 glucose, 10 HEPES; pH adjusted to 7.4 with NaOH before plating on poly - d - lysine (0.02 mg / ml; BD Bioscience) and laminin (0.02 mg / ml; Sigma - Aldrich)-
coated coverslips.