Figure 3.

C_m changes depend strongly on voltage-gated Ca²⁺ entry. (a) Omission of extracellular Ca²⁺ (nominally Ca²⁺-free extracellular solution/2 mM EGTA/3 mM MgCl₂) reversibly abolished both voltage-gated Ca²⁺ entry (asterisks, right axis reversed) and C_m increments (filled circles) stimulated by 100-ms depolarizations to −15 mV. (b) The voltage dependence of ΔC_m caused by depolarizations of 200 ms (open circles, two cells) and 25 ms (small filled circles, seven cells) was similar to that of the Ca²⁺ current (large asterisks, 200 ms; small asterisks, 25 ms). The current–voltage relation is shifted in a positive direction, most likely because of surface charge screening. (c) Nifedipine (3 μM; dark gray) blocked about 50% of both the Ca²⁺ current (Lower) and the ΔC_m (Upper) in this representative example, whereas 5 mM Co²⁺ (light gray, in the presence of Ca²⁺) led to full suppression of both Ca²⁺ current and ΔC_m. Cells were depolarized to −15 mV for 50 ms. ΔC_m and current traces were smoothed by box averaging (n = 5) and binomial smoothing (n = 5), respectively. All experiments (a–c) were performed in perforated-patch configuration.