Effects of cholesterol levels on the excitability of rat hippocampal neurons

Figures & data

Figure 1.  Effect of cholesterol levels on action potentials. (A) Effect of cholesterol depletion and enrichment by cholesterol-free (10 mM MβCD) and cholesterol-loaded MβCD (200 µM MβCD/Chol) on action potentials. The inset shows the superimposed AP, which were aligned at the time of maximal upstroke to allow comparison of the time course of the AP at double expanded time scale. (B) Changes in firing patterns of AP induced by cholesterol-free (representative of 6 neurons) and cholesterol-loaded MβCD (MβCD/Chol, representative of 5 neurons). (C) Plots of AP amplitude and time constant for control, depletion (MβCD) and enrichment (MβCD/Chol) of cholesterol (*p<0.05; **p<0.01).

Figure 2.  Effect of cholesterol levels on the I_K currents. (A) Representative current traces for the I_K currents for cholesterol-depleted (10 mM MβCD) and enriched (200 µM MβCD/Chol) neurons. (B) Statistics on the ratio (I_K/I_Ko) values of the steady-state outward I_K current before (I_Ko) and after (I_K) treatment with MβCD (1–10 mM) or MβCD/Chol. The steady-state outward I_K current (+10 mV) was measured as mean value in a range from 85–100% of the current trace.

Figure 3.  Effect of cholesterol levels on the I_A currents. (A) Representative current traces for the I_A currents for cholesterol depleted and enriched neurons. Inset: Time course of I_A decay that was fitted with two exponential functions. Illustrated are representative I_A current recorded after cholesterol depletion with 10 mM MβCD. A representative fitted curve is superimposed in grey (shown in red in Molecular Membrane Biology online). (B) Summary of parameters derived from the fitting at a test pulse of +10 mV in the control condition, in the presence of 10 mM MβCD, or in the presence of 200 µM MβCD/chol. (C) Statistics on the ratio (τ_fast/τ_fasto) values of the fast time constant component of I_A before (τ_fasto) and after (τ_fast) treatment with MβCD (1–10 mM) or MβCD/Chol. Times of each experiment are indicated in the parenthesis.

Figure 4.  Activation and inactivation curves for I_K (A) and I_A. (B) in control and MβCD-exposed neurons. For activation curves, the normalized conductance (G/Gmax) is plotted against the membrane potential and fitted with the Boltzmann equation: V_1/2 equals to −16.2 and −32.9 mV (control), or −9.2 and −35.5 mV (10 mM MβCD) for I_K and I_A, respectively. For inactivation curves, the normalized current (I/Imax) is plotted against the conditioning membrane potential and fitted with the Boltzmann equation: V_1/2 equals to −73.8 and −86.6 mV (control), or −77.0 and −90.2 mV (10 mM MβCD) for I_K and I_A, respectively.

Figure 5.  Effect of cholesterol depletion by MβCD on AP and outward K⁺ currents in the presence 4-AP and TEA. (A) APs generated from the same neuron in the control condition, in the presence of both TEA (5 mM) and 4-AP (3 mM), and in the presence of 10 mM MβCD after treatment with both TEA and 4-AP (representative of 5 neurons). (B) I_K current from the same neuron at +30 mV in the control condition, in the presence of 5 mM TEA, and in the presence of 10 mM MβCD after treatment with TEA (n=4). (C) I_A current from the same neuron at +30 mV in the control condition, in the presence of 4 mM 4-AP, and in the presence of 10 mM MβCD after treatment with 4-AP (n=5).