Figure 1

Biophysical properties of Gr28bD in Xenopus oocytes. (A) Temperature response: oocytes injected with Gr28bD cRNA display temperature-activated inward current in response to temperature steps. Control oocytes injected with RNAse-free water exhibit no significant current. (B) Response of Gr28bD current to slow temperature ramps (≈2.5 °C/60 s). (C) Temperature sensitivity: the logarithmic plot of normalized Gr28bD current versus slow ramp temperature exhibits two ranges of temperature sensitivity. Red and blue lines represent linear fits to data in each range (14–19 °C and 21–35 °C). Q₁₀ values were calculated using the equation Q₁₀ = 10^10×s, where s is the slope of the linear fit. The average estimates are shown (n = 12). (D) Voltage response: control and Gr28bD currents in response to voltage steps at two different temperatures. Endogenous currents are small at all voltages and temperatures. (E) Current-voltage relationships for GR28bD-expressing and control oocytes at 10 and 35 °C, as obtained with the voltage step protocol in D. Gr28bD current does not show voltage sensitivity at the tested temperatures. The symbols are as in D. (F) Ionic selectivity: Gr28bD currents were obtained as in E, at 35 °C, with Na⁺ partially replaced by NMDG⁺ in the external solution (96 mM Na⁺ : 0 mM NMDG⁺, 48 : 48, and 2 : 94). The measured reversal potentials were (in mV): −12.0 ± 0.7, −23.7 ± 0.2, and −59.0 ± 0.9, respectively. The holding voltage was −60 mV in all experiments. Data shown in A, B, C, and D are representative examples. In E and F, data points are mean ± SEM (n = 6–8). The currents were obtained under ND96 solution (see Methods), except where otherwise noted.