Fig. 3. Effects of store Ca²⁺-ATPase inhibitors on [Ca²⁺]_i in individual cells after establishment of the sustained phase of the progesterone-induced response. (A) Application of 1 µM thapsigargin (bar above traces) had no effect on [Ca²⁺]_i in most cells (lines without symbols) but in approximately 2% of cells there was a sustained increase in [Ca²⁺]_i (). Responses of 15 cells are shown. (B) 10 µM thapsigargin (bar above traces) was similarly ineffective in most cells (lines without symbols) but induced a sustained elevation of [Ca²⁺]_i in approximately one third of cells (,,). Responses of six cells are shown. (C) 40 µM bis-phenol added 10 minutes after progesterone (arrow) caused a sustained elevation of [Ca²⁺]_i in 74% of cells (lines without symbols), occasionally preceded by a [Ca²⁺]_i transient (), a few cells showing no clear response (). Responses of six cells are shown. (D) After application of 1 µM thapsigargin (bar above traces), subsequent application of 40 µM bis-phenol (bar above traces) caused a sustained rise in [Ca²⁺]_i in 40% of thapsigargin-insensitive cells. Responses of five cells are shown. Trace without symbols is a non-responsive cell.