Evidence for a cannabinoid receptor in sea urchin sperm and its role in blockade of the acrosome reaction

Abstract

Delta-9-tetrahydrocannabinol ((-)delta 9 THC), the primary psychoactive cannabinoid in marihuana, reduces the fertilizing capacity of sea urchin sperm by blocking the acrosome reaction that normally is stimulated by a specific ligand in the egg's jelly coat. The bicyclic synthetic cannabinoid [3H]CP-55,940 has been used as a ligand to demonstrate the presence of a cannabinoid receptor in mammalian brain. We now report that [3H]CP-55,940 binds to live sea urchin (Strongylocentrotus purpuratus) sperm in a concentration, sperm density, and time-dependent manner. Specific binding of [3H]CP-55,940 to sperm, defined as total binding displaced by (-)delta 9THC, was saturable: KD 5.16 +/- 1.02 nM; Hill coefficient 0.98 +/- 0.004. This suggests a single class of receptor sites and the absence of significant cooperative interactions. Sea urchin sperm contain 712 +/- 122 cannabinoid receptors per cell. Binding of [3H]CP-55,940 to sperm was reduced in a dose-dependent manner by increasing concentrations of CP-55,940, (-)delta 9THC, and (+)delta 9THC. The rank order of potency to inhibit binding of [3H]CP-55,940 to sperm and to block the egg jelly stimulated acrosome reaction was: CP-55,940 > (-)delta 9THC > (+)delta 9THC. These findings show that sea urchin sperm contain a stereospecific cannabinoid receptor that may play a role in inhibition of the acrosome reaction. The radioligand binding data obtained with live sea urchin sperm are remarkably similar to those previously published by other investigators using [3H]CP-55,940 on mammalian brain and nonneural tissues. The cannabinoid binding properties of this receptor appear to have been highly conserved during evolution. We postulate that the cannabinoid receptor may modulate cellular responses to stimulation.

Evidence that anandamide‐signaling regulates human sperm functions required for fertilization

“…The potent cannabinoid agonist [ 3 H]CP-55,940 (DuPont NEN, Boston, MA) was used to detect cannabinoid receptors in human sperm, as described previously (Devane et al, 1988;Chang et al, 1993;Matsuda, 1997). Semen samples were diluted with yolk buffer transport medium (TYB Medium, ZDL, Inc., Lexington, KY) (Bolanos et al, 1983), and shipped over ice to the University of Connecticut.…”

“…Higher albumin levels sequester cannabinoids, and reduce binding of ligands to sperm (Chang et al, 1993). Control or test medium was layered over washed sperm pellets (see above).…”

“…Previous studies showed that [ 3 H]CP-55,940 binds with high affinity to cannabinoid receptors in mammalian tissues and sea urchin sperm (Chang et al, 1993;Matsuda, 1997 …”

“…Sea urchin sperm express functional cannabinoid receptors similar to those in mammalian organs (Chang et al, 1993). While AEA and THC enhance sea urchin sperm motility, they inhibit fertilization by blocking the acrosome reaction Schuel et al, 1991aSchuel et al, ,b, 1994Schuel et al, , 1999.…”

“…This finding, together with our discovery of functional cannabinoid receptors in sea urchin sperm, led us to postulate that human sperm might contain cannabinoid receptors (Chang et al, 1993;Schuel et al, 1994). Subsequent studies on whole organs showed that AEA is synthesized in rodent testis, oviduct, and uterus (Paria et al, 1995;Sugiura et al, 1996;Schmid et al, 1997;Paria and Dey, 2000).…”