changes in the sperm head of wild-type mice monitored with single cell imaging. (A) Representative recordings of [Ca2+]i changes (represented as normalized Fluo-4 fluorescence changes) in response to application of BSA (5 mg/ml; indicated by vertical arrow) to a bath containing 2 mM Ca2+ or no Ca2+ (with 5 mM EGTA). Some cells also had a second phase of [Ca2+]i rise (see Figure 2A). Ionomycin (5 μM, used as a control) caused a [Ca2+]i rise in the absence of extracellular Ca2+ by releasing intracellular Ca2+. (B) Dose -dependence of peak amplitude of the BSA-induced Ca2+ responses.