Fig. 3. Mobilisation of stored Ca²⁺ by NO does not involve cGMP. (A) 100 µM 8-bromo cGMP causes rapid elevation of [Ca²⁺]_i in human sperm. Responses of six cells are shown. (B) Response to 8-bromo cGMP is greatly reduced and slowed in cells exposed to cGMP in low-Ca²⁺ saline. Responses of five cells are shown. (C)Ca²⁺ dependence of the response to 100 µM 8-bromo cGMP. Light-grey bars show responses of cells bathed in sEBSS (72 cells; two experiments); dark-grey bars show cells bathed in low-Ca²⁺ sEBSS (122 cells; three experiments). (D) Pre-treatment with the sGC inhibitor ODQ (10 µM; white bar) does not inhibit the increase in [Ca²⁺]_i induced by exposure to 100 µM spermine NONOate (arrow). Responses of seven cells are shown. (E) Mean normalised increase in fluorescence 10 minutes after application of 100 µM spermine NONOate under control conditions (208 cells; three experiments) and after pre-treatment with 10 µM ODQ (267 cells; three experiments). Pre-treatment did not modify the amplitude of the response.