ATP-sensitive K+ channels were inhibited by including 5 mM Mg-ATP in the pipette solution. All chemicals including the www.selleckchem.com/products/17-AAG(Geldanamycin).html (+)MK801 and (−)MK801 enantiomers were purchased from Sigma Chemical. We used the conventional whole-cell configuration of the patch clamp technique to record membrane currents and Em
by using an EPC8 (HEKA, Mahone Bay, Canada) patch clamp amplifier. Data were digitized using custom-built software (R-clamp, by Dr. Ryu SY) at a sampling rate of 5 kHz, low-pass filtered at 1 kHz, and then stored on a computer. Voltage pulse generation was also controlled using R-clamp software. Patch pipettes were pulled from borosilicate capillary tubes (Clark Electromedical Instruments, Pangbourne, UK) by using a PP-83 puller (Narishige, Tokyo, Japan). We used patch pipettes with a resistance of 2–4 MΩ when filled with the pipette solution listed above. Recordings were started 4–6 min after establishing the whole-cell configuration to allow adequate cell dialysis of the pipette solution. The liquid–liquid junction potential between the NT and pipette solutions (calculated from ion mobilities) was approximately −4.5 mV PARP inhibitor at 25 °C. This junction potential was not corrected for when analyzing data. Therefore, the true Em values might be 4–5 mV more negative (hyperpolarized) than those reported here. All experiments were conducted at room temperature
(20–25 °C). Origin 6.0 software (Microcal Software, Inc., Northampton, MA, USA) was used for data analysis. Half-inhibition concentration (IC50) and Hill coefficients (n) were obtained by fitting concentration–response data to the Logistic function in the Origin software. Activation kinetics was calculated by fitting the data to a single exponential. The time course of current inactivation was also fitted to a single exponential function. Steady-state activation curves were fitted with the following Boltzmann equation: y = 1/1 + exp (−(V−V1/2)/k),where k is the slope factor, V is the
test potential, and V1/2 is the voltage at which half-maximal conductance is obtained. The steady-state voltage dependence of inactivation was investigated using a double-pulse voltage protocol; peak currents were measured by applying a of 250-ms test potential to +40 mV, and 10-s preconditioning pulses were varied from −60 to +50 mV (in 10-mV steps) in the presence and absence of MK801. The resulting steady-state inactivation data were fitted to the following Boltzmann equation: y = 1/[1 + exp (V− V1/2)/k],where V is the preconditioning potential, V1/2 is the potential corresponding to the half-inactivation point, and k is the slope value. The results are shown as means ± SEM. Paired or independent Student’s t tests were used to test for significance as appropriate, and P < 0.