Chemosensory Ca2+ dynamics correlate with diverse behavioral phenotypes in human sperm.

In the female reproductive tract, mammalian sperm undergo a regulated sequence of prefusion changes that "prime" sperm for fertilization. Among the least understood of these complex processes are the molecular mechanisms that underlie sperm guidance by environmental chemical cues. A "hard-wired" Ca(2+) signaling strategy that orchestrates specific motility patterns according to given functional requirements is an emerging concept for regulation of sperm swimming behavior. The molecular players involved, the spatiotemporal characteristics of such motility-associated Ca(2+) dynamics, and the relation between a distinct Ca(2+) signaling pattern and a behavioral sperm phenotype, however, remain largely unclear. Here, we report the functional characterization of two human sperm chemoreceptors. Using complementary molecular, physiological, and behavioral approaches, we comparatively describe sperm Ca(2+) responses to specific agonists of these novel receptors and bourgeonal, a known sperm chemoattractant. We further show that individual receptor activation induces specific Ca(2+) signaling patterns with unique spatiotemporal dynamics. These distinct Ca(2+) dynamics are correlated to a set of stimulus-specific stereotyped behavioral responses that could play vital roles during various stages of prefusion sperm-egg chemical communication.

G protein-coupled receptor signaling via Src kinase induces endogenous human transient receptor potential vanilloid type 6 (TRPV6) channel activation.

Ca(2+) homeostasis plays a critical role in a variety of cellular processes. We showed previously that stimulation of the prostate-specific G protein-coupled receptor (PSGR) enhances cytosolic Ca(2+) and inhibits proliferation of prostate cells. Here, we analyzed the signaling mechanisms underlying the PSGR-mediated Ca(2+) increase. Using complementary molecular, biochemical, electrophysiological, and live-cell imaging techniques, we found that endogenous Ca(2+)-selective transient receptor potential vanilloid type 6 (TRPV6) channels are critically involved in the PSGR-induced Ca(2+) signal. Biophysical characterization of the current activated by PSGR stimulation revealed characteristic properties of TRPV6. The molecular identity of the involved channel was confirmed using RNA interference targeting TrpV6. TRPV6-mediated Ca(2+) influx depended on Src kinase activity. Src kinase activation occurred independently of G protein activation, presumably by direct interaction with PSGR. Taken together, we report that endogenous TRPV6 channels are activated downstream of a G protein-coupled receptor and present the first physiological characterization of these channels in situ.

Subunit-specific P2X-receptor expression defines chemosensory properties of trigeminal neurons.

The facial innervation pattern of trigeminal nerve fibres comprises the innervation of the nasal epithelium, where free trigeminal nerve endings contribute to detection and discrimination of chemical stimuli including odourants. The signal transduction mechanisms in sensory nerve endings underlying perception of chemical stimuli remain widely uncovered. Here, we characterized trigeminal ATP-activated P2X receptors in cultured rat trigeminal neurons and investigated their role in chemoperception. We identified a new subpopulation of neurons lacking typical nociceptive characteristics and expressing homomeric P2X(2) receptors. Using a certain group of chemicals known as trigeminal stimuli we found no direct activation of trigeminal neurons, but a modulation of P2X(2) receptor mediated currents. In contrast, P2X(3) receptor mediated currents of nociceptive trigeminal neurons remained unaffected by the tested chemicals. Therefore, we assume a functional role for the newly identified subpopulation in chemodetection of certain trigeminal stimuli.