Fig 1.

PMA lowers the calcium threshold for secretion in gonadotropes. Steady UV illumination generates ramp [Ca²⁺]_i increases with intracellular caged Ca²⁺ and measures [Ca²⁺]_i by using a Ca²⁺ indicator, fura-6F. Simultaneous time courses of [Ca²⁺]_i and C_m for a single control gonadotrope (A) and for a PMA-treated (for 2–3 min) gonadotrope (B). Note at the same [Ca²⁺]_i level, C_m only begins to increase in the control cell, whereas it already takes off in the PMA-treated cell. At the end of the experiments, the cells were challenged by 5 nM GnRH to verify them as gonadotropes (Lower).