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

OBJECTIVE:
Evaluation of the presence of a Ca(2+)-regulated membrane guanylate cyclase signal transudation system in the spermatozoa.
DESIGN:
Experimental study.
SETTING:
Research 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 Ca(2+)-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 Ca(2+). The transduction component of this machinery is the rod outer segment membrane guanylate cyclase type 1 (ROS-GC1). The enzyme coexists with three Ca(2+)-dependent modulators: guanylate cyclase activating protein type 1 (GCAP1), S100B and neurocalcin delta. 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 Ca(2+)-modulated ROS-GC1 transduction system may be a part of the fertilization machinery.