Figure 4. Depolarization induced the increase in the [Ca²⁺]_i and the secretory activity in newborn and adult melanotrophs.

A, changes in [Ca²⁺]_i were triggered by a train of 50 depolarization pulses (40 ms) from −80 mV to 10 mV and 100 ms interval (B) measured with fura-6F. The [Ca²⁺]_i increased rapidly, reached a plateau at the concentration of several micromolar after 3 s of stimulation and decreased to the resting value after the end of stimulation. Note similar time profile of [Ca²⁺]_i in newborn (red trace) and adult melanotrophs (black trace). C, normalized cumulative membrane capacitance change to the resting membrane capacitance (norm. ΔC_m) did not tightly follow the changes in [Ca²⁺]_i. Norm. ΔC_m increased slower than [Ca²⁺]_i, and persisted despite [Ca²⁺]_i reaching the maximum. After the end of the stimulation, melanotrophs reached their C_m peak values followed by slow endocytosis for several tens of seconds to reach the steady state level.