Fig. 5. Effect of 5-HT, NH₄Cl or KCl on the cAMP concentration of Spisula oocytes. (A) Oocytes were either treated with 5-HT (5 µM, ) or left untreated (). Aliquots were removed at different times and processed for cAMP determinations, and the results are expressed as a percentage of the initial cAMP concentration of untreated oocytes. (B) A similar experiment using oocytes pre-incubated in the presence of forskolin and IBMX (60/65 µM) for 15 minutes prior to the addition of 5-HT. The insets depict the corresponding time course of GVBD (±s.e.m.) for sampled oocytes. Mean results of three experiments are shown. (C) shows the effect of adding 5-HT (5 µM), KCl (10% v/v) or NH₄Cl (10 mM) on oocyte cAMP concentration at indicated times, as compared with untreated oocytes. Percentages of GVBD scored 15 minutes after adding 5-HT, KCl or NH₄Cl were 100%, 100% and 0% percent, respectively. Mean results (±s.e.m.) of three experiments are shown. (D) shows the effect of adding K⁺ on oocyte cAMP concentration. Various amounts of isotonic KCl (0.52 M) were added to oocytes to obtain the final concentrations shown (% v/v). Oocytes were sampled 10 minutes later for determination of cAMP concentration, as described in the Materials and Methods. GVBD, as scored after 15 minutes, had occurred only at KCl concentrations of 5 and 10% (v/v), in 86% and 100% of the oocytes, respectively, with all lower KCl concentrations resulting in less than 2% GVBD. Mean results (±s.e.m.) of three experiments.