Figure 4.

Possible mI_CAT inhibition by a diffusible intracellular factor. (a) Delayed current activation when carbachol was applied immediately after break-through (trace 1; note that PSS has been already replaced by high-Cs⁺ external solution before establishing the whole-cell configuration) compared to standard 3 min equilibration experiment (trace 2). (b, c) Lack of intracellular ATP (20 mM) effect on the 100 μM carbachol-induced mI_CAT I–V relationship and corresponding cation conductance activation curve. Cell dialysis with PA-free pipette solution containing 1 mM ATP appears to be sufficient to remove PAs from the cytoplasm. (d) Changes of [Ca²⁺]_i in single ileal smooth muscle cell voltage-clamped at −40 mV during the application of 100 μM carbachol in Ca²⁺-free high-Cs⁺ external solution. I–V relationships in perforated patch experiments were measured when [Ca²⁺]_i was stabilized at about 100 nM, as indicated. (e, f) Carbachol (100 μM) induced mI_CAT I–V relationship and corresponding cation conductance activation curve measured using perforated patch configuration. Mean current amplitudes using this (grey column, n=7) and conventional whole-cell configuration (black column, n=12) are shown in the inset.