Figure 5.

Extracellular La³⁺ enhances C-type inactivation in T449A and T449T (i.e., wild type) channels. (A) The black and the red trace are I_K from an outside-out patch before and after exposure to 50 µM La³⁺, which virtually eliminated I_K (blue trace). I_K was elicited by 1.5-s pulses from –90 to 0 mV every 62 s. (B) Peak I_K through T449A channels before and during exposure to 5 µM La³⁺ in the extracellular solution. Similar results were obtained in four patches. (C) Peak I_K through T449T (wild type) channels before, during, and after washout of 5 µM La³⁺ in the extracellular solution. The patch was held at −90 mV except to measure the currents as illustrated in the insets. Similar results were obtained in four patches. The extracellular solution contained (mM) 130 NaCl, 4 KCl, 2 CaCl₂, 2 MgCl₂, 10 glucose, and 10 HEPES, pH 7.4, plus 5 µM La³⁺ in blue traces. The internal solution contained (mM) 140 KCl, 2 MgCl₂, and 10 HEPES, pH 7.2.