Model organisms: new insights into ion channel and transporter function. L-type calcium channels regulate epithelial fluid transport in Drosophila melanogaster |
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Authors: | MacPherson M R Pollock V P Broderick K E Kean L O'Connell F C Dow J A Davies S A |
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Affiliation: | Institute of Biomedical and Life Sciences, Division of Molecular Genetics, University of Glasgow, Glasgow G11 6NU, United Kingdom. |
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Abstract: | The neuropeptide CAP2b stimulates fluid transport obligatorily via calcium entry, nitric oxide, and cGMP in Drosophila melanogaster Malpighian (renal) tubules. We have shown by RT-PCR that the Drosophila L-type calcium channel alpha1-subunit genes Dmca1D and Dmca1A (nbA) are both expressed in tubules. CAP2b-stimulated fluid transport and cytosolic calcium concentration ([Ca2+]i) increases are inhibited by the L-type calcium channel blockers verapamil and nifedipine. cGMP-stimulated fluid transport is verapamil and nifedipine sensitive. Furthermore, cGMP induces a slow [Ca2+]i increase in tubule principal cells via verapamil- and nifedipine-sensitive calcium entry; RT-PCR shows that tubules express Drosophila cyclic nucleotide-gated channel (cng). Additionally, thapsigargin-induced [Ca2+]i increase is verapamil sensitive. Phenylalkylamines bind with differing affinities to the basolateral and apical surfaces of principal cells in the main segment; however, dihydropyridine binds apically in the tubule initial segment. Immunocytochemical evidence suggests localization of alpha1-subunits to both basolateral and apical surfaces of principal cells in the tubule main segment. We suggest roles for L-type calcium channels and cGMP-mediated calcium influx in both calcium signaling and fluid transport mechanisms in Drosophila. |
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