Signaling by intracellular Ca²⁺ and H⁺ in larval mosquito (Aedes aegypti) midgut epithelium in response to serosal serotonin and lumen pH

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• 作者：David F. Moffett^a ; ^{dmoffett@wsu.edu} ; Urmila Jagadeshwaran^a ; Zeping Wang^a ; ¹ ; Hana M. Davis^a ; Horst Onken^a ; ^b ; Greg G. Goss^c
• 关键词：Mosquito ; Aedes aegypti ; Serotonin ; Serotonin receptor ; Midgut ; Alkalinization ; Acidification ; Epithelium ; Intracellular calcium ; Cyclic AMP
• 刊名：Journal of Insect Physiology
• 出版年：2012
• 期刊代码：92_00221910
• 类别：bio
• 出版时间：April, 2012
• 卷：58
• 期：4
• 页码：506-512
• 文件大小：635 K

摘要

The midgut of larval mosquitoes (Aedes aegypti) mediates a cycle of alkali secretion in the anterior segment (AMG) followed by partial reacidification in the posterior segment (PMG); both processes are serotonin-dependent. Here we report that intracellular Ca²⁺ as indicated by Fura-2 fluorescence, is elevated in both tissues in response to serotonin, but the time courses differ characteristically in the two gut segments, and Ca²⁺-free solution abolishes the serotonin response in AMG, but not in PMG, whereas Thapsigargin, an inhibitor of endoplasmic Ca²⁺ transport, abolished responsiveness to 5-HT in PMG. These results suggest the origins for the Ca²⁺ signal differ between the two tissues. Quantitative real-time RT-PCR revealed expression of 5 putative 5-HT receptor types in AMG, including 5-HT₂-like receptors which would be expected to initiate a Ca²⁺ signal. None of these receptors were highly expressed in PMG. Cyclic AMP (cAMP) is a secretagogue for both tissues, but H89, an inhibitor of Protein Kinase A (PKA), is also a secretagogue, suggesting that the stimulatory effect of cAMP involves a non-PKA pathway. Cytochalasins B and D block the effect of 5-HT in AMG, suggesting a vesicle-fusion mechanism of activation of the basal V-ATPase in this tissue. Finally, in PMG, elevation of luminal pH increases and decreases intracellular pH as measured by BCECF fluorescence. These responses suggest that the rate of acid secretion by PMG might be responsive to local demand for luminal reacidification as well as to serosal serotonin.