Figure 5.

50 mM TEA⁺ fails to block ELIC. (A) Macroscopic current responses to 5-s pulses of 10 mM cysteamine recorded at –80 mV in the outside-out configuration. The responses were recorded without TEA⁺ in either barrel (left) or in the presence of 50 mM TEA⁺ flowing through both barrels of the theta-type perfusion tubing (middle). Because ELIC displayed marked rundown in outside-out patches, these traces were not recorded sequentially. Instead, individual patches of membrane were exposed to cysteamine pulses either in the absence or the presence of TEA⁺. In separate recordings, TEA⁺ was also applied to the intracellular side of outside-out patches (right). The solutions flowing through the two barrels of the perfusion tubing were (in mM) 142 KCl, 5.4 NaCl, 1.8 CaCl₂, 1.7 MgCl₂, and 10 HEPES/KOH, pH 7.4 with or without cysteamine and with or without TEA⁺. In the schematic representations of the theta-tubing perfusion, arrows indicate the application of external TEA⁺. (B) Peak-current amplitudes recorded in response to the application of cysteamine in the presence of external 50 mM TEA⁺ or internal 5 mM TEA⁺ normalized to the peak value observed in the absence of external or internal TEA⁺. (C) Time constants of desensitization during the application of cysteamine in the presence of external 50 mM TEA⁺ or internal 5 mM TEA⁺ normalized to the time constant fitted to TEA⁺-free recordings. The values plotted in B and C are means obtained from 8 (external 50 mM TEA⁺) and 5 (internal 5 mM TEA⁺) patches; error bars are the corresponding standard errors. Note the lack of effect of millimolar TEA⁺ applied to either side of the membrane.