Figure 4. The ZERO variant is not regulated by glucocorticoids.

A, representative single channel traces from isolated inside-out patches from dexamethasone pre-treated HEK 293 cells expressing ZERO variant channels before and 10 min after application of 1 mm cAMP to the intracellular face of the patch. Patches containing ZERO channels were exposed to 0.2 μm[Ca²⁺]_i and 1 mm ATP in physiological potassium gradients and depolarised to +40 mV as described in Methods. B, representative time course of ZERO channel activity from vehicle-treated cells in the presence (+cAMP, ▪) or absence (-cAMP, □) of cAMP. Activity is expressed as a percentage of the activity at time −10 min before cAMP application and averaged over 1 min for each data point. Open horizontal bar indicates the period of cAMP application for the +cAMP patch. C, summary of the effect of cAMP application to the intracellular face of patches from ZERO-expressing HEK 293 cells pre-treated for 2 h with vehicle (n = 8) or 1 μm dexamethasone (n = 8) prior to patch excision. The specific PKA inhibitor peptide PKI_5–24 was applied to the intracellular face of inside-out patches 5 min before application of cAMP in vehicle (n = 4) or dexamethasone-treated (n = 6) cells. All data are expressed as the percentage change of pre-treatment BK channel activity measured at +40 mV in the presence of 0.2 μm[Ca²⁺]_i and 1 mm ATP as described in Methods. The bars show means and s.e.m. **P < 0.01 compared with vehicle-treated cAMP group.