Cystic fibrosis transmembrane conductance regulator chloride channel blockers: Pharmacological, biophysical and physiological relevance

Figure 6 Channel block by cytoplasmic anions in intact cells and its dependence on extracellular anions. A: During patch clamp recording from intact cells, cystic fibrosis transmembrane conductance regulator (CFTR) channels in the cell membrane are subject to block anions present in the cytoplasm of the cell (left). This blocking effect is lost when the patch of membrane is excised into the inside-out patch configuration (right); B: Example of this effect during macroscopic CFTR current recording from a baby hamster kidney cell expressing human CFTR, as described in detail[82]. Currents were recorded before (red) and after (black) excision of the patch from the cell, during voltage steps to between -100 mV and +100 mV in 20 mV increments from a holding potential of 0 mV. Dotted line represents the zero current level; C: Current-voltage relationships for the currents shown in (B). Note the outward rectification of the relationship in cell-attached recording (red) due to voltage-dependent channel block, and loss of this blocking effect following patch excision (black); D: Similar example current-voltage relationships from baby hamster kidney cell membrane patches when the extracellular solution contained 150 mmol/L NaCl (left) or 150 mmol/L NaHCO3^- (right), as described in detail[101]. Note that the apparent degree of block in cell attached patches (red) is stronger when the extracellular solution contains HCO3^- compared to Cl^-, an effect quantified in detail in ref. [101].