Chemosignal transduction in the vomeronasal organ of garter snakes: Ca(2+)-dependent regulation of adenylate cyclase.
Earthworm shock secretion contains a 20-kDa vomeronasally mediated chemoattractive protein for garter snakes. Both the ligand-receptor binding and the chemoattractivity of ES20 are Ca(2+)-dependent. When ES20 binds to its G-protein-coupled receptors in the vomeronasal epithelium, the inositol 1,4,5-trisphosphate (IP3) level is increased, but the level of cAMP is reduced. Furthermore, forskolin-stimulated levels of cAMP are completely blocked by ES20-receptor binding or by Ca2+ alone and the effect of calcium ions can be nullified by EGTA. Previously, we hypothesized that the decrease in cAMP was due to activation of a Ca(2+)-dependent phosphodiesterase. In the present study, we provide evidence that the decrease in cAMP is due mainly to the regulation of adenylate cyclase (AC) activity by Ca2+ or is indirectly mediated by ES20. Results obtained with intact vomeronasal sensory epithelium suggest that the binding of ES20 to its receptors facilitates generation of IP3 which mobilizes intracellularly sequestered Ca2+, resulting in an increase of cystosolic Ca2+. A further increase in cytosolic Ca2+ occurs through Ca2+ influx from extracellular sources. Garter snake vomeronasal AC does not require calmodulin for its activity and shows a biphasic response to increasing concentrations of Ca2+; its activity is modulated both positively and negatively by this bivalent cation.
Wang
D
D
Department of Biochemistry, State University of New York Health Science Center at Brooklyn, New York 11203, USA.
Chen
P
P
Liu
W
W
Li
C S
CS
Halpern
M
M
D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002630:Chemotactic Factors; D005576:Colforsin / Q000494:pharmacology; D017812:Colubridae; D004597:Electroshock; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008954:Models, Biological; D009812:Odorants; D009835:Oligochaeta; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D019147:Vomeronasal Organ / Q000187:drug effects / Q000502:physiology*
D037361:Adenylate Cyclase Toxin; D002630:Chemotactic Factors; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000262:Adenylyl Cyclases; D008274:Magnesium; D002118:Calcium