Rod outer segment membrane guanylate cyclase type 1 (ROS-GC1) calcium-modulated transduction system in the sperm

ObjectiveEvaluation of the presence of a Ca2+-regulated membrane guanylate cyclase signal transudation system in the spermatozoa.DesignExperimental study.SettingResearch university laboratory.Patient(s)Human sperm obtained from healthy donors who met the criteria of the World Health Organization for normozoospermia and bovine semen collected from bulls of proven fertility.Intervention(s)Radioimmunoassay and immunohistochemistry of human and bovine spermatozoa.Main Outcome Measure(s)The membrane guanylate cyclase activity and the presence of membrane guanylate cyclase transduction machinery components in the spermatozoa.Result(s)The identity of a Ca2+-modulated membrane guanylate cyclase transduction machinery in human and bovine spermatozoa has been documented. The machinery is both inhibited and stimulated within nanomolar to semimicromolar range of free Ca2+. The transduction component of this machinery is the rod outer segment membrane guanylate cyclase type 1 (ROS-GC1). The enzyme coexists with three Ca2+-dependent modulators: guanylate cyclase activating protein type 1 (GCAP1), S100B and neurocalcin δ. ROS-GC1 and its modulators are present in the heads and tails of both species' spermatozoa.Conclusion(s)The coexpression of ROS-GC1 and its activators in spermatozoa suggests that the Ca2+-modulated ROS-GC1 transduction system may be a part of the fertilization machinery.