Model organisms: New insights into ion channel and transporter function. L-type calcium channels regulate epithelial fluid transport in Drosophila melanogaster

The neuropeptide CAP(2b) stimulates fluid transport obligatorily via calciu m entry, nitric oxide, and cGMP in Drosophila melanogaster Malpighian (rena l) tubules. We have shown by RT-PCR that the Drosophila L-type calcium chan nel alpha (1)-subunit genes Dmca1D and Dmca1A (nbA) are both expressed in t ubules. CAP(2b)-stimulated fluid transport and cytosolic calcium concentrat ion ([Ca2+](i)) increases are inhibited by the L-type calcium channel block ers verapamil and nifedipine. cGMP-stimulated fluid transport is verapamil and nifedipine sensitive. Furthermore, cGMP induces a slow [Ca2+](i) increa se in tubule principal cells via verapamil- and nifedipine-sensitive calciu m entry; RT-PCR shows that tubules express Drosophila cyclic nucleotide-gat ed channel (cng). Additionally, thapsigargin-induced [Ca2+](i) increase is verapamil sensitive. Phenylalkylamines bind with differing affinities to th e basolateral and apical surfaces of principal cells in the main segment; h owever, dihydropyridine binds apically in the tubule initial segment. Immun ocytochemical evidence suggests localization of alpha (1)-subunits to both basolateral and apical surfaces of principal cells in the tubule main segme nt. We suggest roles for L-type calcium channels and cGMP-mediated calcium influx in both calcium signaling and fluid transport mechanisms in Drosophi la.