Cyclic nucleotide crosstalk in salivary glands from partially fed Dermacentor variabilis (Say)

• Published in: Journal of insect physiology 2009-09, Vol.55 (9), p.805-812
• Main Authors: Blaudow, Robert A., Coons, Lewis B., Cole, Judith A.
• Format: Article
• Language: English
• Subjects: adenylate cyclase; Animals; arthropod pests; calcium; Crosstalk; cyclic AMP; cyclic GMP; Cyclic GMP - metabolism; Cyclic nucleotide; cyclic nucleotides; Dermacentor variabilis; dopamine; enzyme activation; enzyme inhibitors; Feeding Behavior; Female; females; forskolin; guanylate cyclase; Guanylate Cyclase - genetics; Guanylate Cyclase - metabolism; Insect Proteins - genetics; Insect Proteins - metabolism; ion transport; Ixodidae; Ixodidae - enzymology; Ixodidae - genetics; Ixodidae - physiology; nitric oxide; nitric oxide synthase; Nucleotides, Cyclic - metabolism; protein kinases; Rabbits; Receptors, Cytoplasmic and Nuclear - genetics; Receptors, Cytoplasmic and Nuclear - metabolism; salivary glands; Salivary Glands - enzymology; Salivary Glands - metabolism; Signal Transduction; Soluble Guanylyl Cyclase; Tick salivary glands; ticks; tissue weight; uptake mechanisms
• ISSN: 0022-1910; 1879-1611
• DOI: 10.1016/j.jinsphys.2009.05.016

Enzyme immunosorbent assays were used to measure cyclic nucleotide concentrations in homogenates of salivary glands from partially fed female Dermacentor variabilis. The adenylyl cyclase activator forskolin (100 μM) increased homogenate cGMP concentrations greater than three-fold over controls. Competitive inhibition of nitric oxide synthase with 1 mM l-NMMA, an l-arginine analog, demonstrated that crosstalk occurs downstream of nitric oxide synthesis. Forskolin-stimulated synthesis of cGMP was diminished 58% by the soluble guanylyl cyclase inhibitor ODQ (2 μM). The protein kinase A selective inhibitor Rp-cAMPS (50 μM) inhibited forskolin-stimulated cGMP by 49%. Whole glands treated with 10 μM dopamine increased cGMP levels two-fold in the presence of 1 mM IBMX. Treatment of whole salivary glands with equimolar concentrations of 8-Br-cAMP and 8-Br-cGMP produced no greater fluid uptake than in glands treated with 8-Br-cGMP alone, suggesting that cAMP and cGMP share a downstream target. The protein kinase G-selective inhibitor Rp-8-pCPT-cGMPS (100 μM) impeded 10 mM 8-Bromo-cGMP-stimulated gland weight increases. Pretreatment with verapamil, a Ca 2+ channel blocker, attenuated cyclic nucleotide-stimulated fluid uptake indicating that whole gland fluid changes are dependent on extracellular Ca 2+. Together, our data suggest that cGMP production is mediated in part by cAMP-dependent activation of soluble guanylyl cyclase. Experiments measuring changes in whole salivary gland weight support the hypothesis that cAMP and cGMP signaling cascades have a common target and that cyclic nucleotide-stimulated fluid movement is dependent on Ca 2+ influx.