RESEARCH INTERESTS
Complete sequencing of human and other genomes has pointed to an extremely important role played by ion channel genes in many physiological processes. Genomic information also highlights the strong evolutionary conservation of molecular mechanisms across species. This makes genetic model systems, such as Drosophila, very powerful for understanding molecular mechanisms underlying most biological phenomena, including membrane excitability.
Using genetic protocols developed in our laboratory, we have identified more than 15 novel mutations that produce striking alterations in calcium and potassium currents in Drosophila. These mutations also affect other functions in flies, such as locomotor ability, heart rate, and/or sensitivity to the effects of pharmacological agents that act on ion channels. Cloning and molecular analysis of nine genes, and the gene products disrupted by these mutations, is underway in the laboratory. This analysis is yielding important information on modulation and regulation of ion channels, and their essential role in maintaining cellular physiology.
In addition to identifying and studying the above mutations, we are using existing mutations to analyze modulation of calcium channels via signal transduction pathways. By combining mutations with pharmacological agents, we have shown that the L-type calcium channels in Drosophila are modulated via the PLC - DAG - PKC pathway and a pathway involving PACAP, PAC1 receptors, adenylyl cyclase, cAMP, and PKA.
Regulation of Ca2+ and K+ channels plays an exceedingly important role in several neuromuscular and other functions, and these channels are targets of a number of pharmacological agents. To link our studies on Drosophila channels to those on channels in other systems, and to understand the mechanisms of ion channel regulation from a broader perspective, we are pursuing electrophysiological and pharmacological studies on the regulation of potassium and calcium channels in mammalian cells, and in cell lines, using patch-clamp recordings.
PUBLICATIONS
Frolov, R. V., Slaughter, M. and Singh, S. (2008). Effects of Celecoxib on Ionic Currents and Spontaneous Firing in Rat Retinal Neurons. Neuroscience. In Press.
Frolov, R. V., Berim, I. and Singh, S. (2008). Inhibition of Delayed Rectifier Potassium Channels and Induction of Arrhythmia - a Novel Effect of Celecoxib and the Mechanism Underlying it. J. Biol. Chem. 283, 1518-1524.
Liu, W., Gnanasambandam, R., Benjamin, J., Kaur, G., Getman, P.B., Siegel, A. J., Shortridge, R. and Singh S. (2007). Mutations in Cytochrome c Oxidase subunit VIa Cause Neurodegeneration and Motor Dysfunction in Drosophila. Genetics 176, 937-946.
Bhattacharya, A., Lakhman, S. S. and Singh, S. Modulation of L-type Ca2+ Channels in Drosophila via a Pituitary Adenylyl Cyclase-activating Polypeptide (PACAP)-mediated pathway. (2004). J. Biol. Chem. 279, 37291-37297
Peri, R., Triggle, D. J. and Singh, S. (2001) Regulation of L-type calcium channels in pituitary GH4C1 cells by depolarization. J. Biol. Chem. 276, 31667-31673.
Peri, R., Padmanabhan, S., Rutledge, A, Singh S. and Triggle, D. J. (2000) Permanently charged chiral 1,4dihydropyridines: molecular probes of L-type calcium channels. Synthesis and Pharmacological characterization of methyl (w-trimethylalkylammonium) 1,4-dihydro-2,6-dimethyl-4-(3nitrophenyl)-3,5pyridinedicarboxylate iodide, calcium channel antagonists. J. Med. Chem. 43: 2906-2914.
Chopra, M., Gu, G.-G. and Singh, S. (2000) Mutations Affecting the Delayed Rectifier Potassium Current in Drosophila. J. Neurogenetics 14: 107-123.
Hegde, P., Gu, G-G., Chen, D., Free, S. J. and Singh, S. (1999) Mutational Analysis of the Shab-encoded Delayed Rectifier K+ channels in Drosophila. J. Biol. Chem. 274, 22109-22113.
Singh, A., and Singh, S. (1999) Unmasking of a Novel Potassium Current in Drosophila by a Mutation and Drugs. J. Neurosci. 19, 6838-6843.
Bhattacharya, A., Gu., G.-G. and Singh S. (1999) Modulation of the Dihydropyridine-Sensitive Calcium Channels in Drosophila by a cAMP-Mediated Pathway. J. Neurobiol. 39, 491-500.
Singh, S. and Wu, C.-F. (1999). Ionic currents in the larval muscles of Drosophila. In: International Review of Neurobiology (Vol. 43 - Neuromuscular Junctions in Drosophila). V. Budnik and S. Gramates, eds. Academic Press. pp. 191-220.
Kraliz, D., Bhattacharya, A. and Singh, S. (1998) Blockade of the Delayed Rectifier Potassium Current in Drosophila by Quinidine and Related Compounds. J. Neurogenet. 12: 25-39.
Gu G.-G. and Singh, S. (1997) Modulation of the dihydropyridine-sensitive Ca2+ channels in Drosophila by a phospholipase C-mediated pathway. J. Neurobiology. 33: 265-275
Kraliz, D. and Singh, S. (1997) Selective blockade of the delayed rectifier potassium current by tacrine in Drosophila. J. Neurobiology 32: 1-10
Gielow, M. L., Gu, G.-G. and Singh, S. S. (1995) Resolution and pharmacological analysis of the voltage dependent calcium channels of Drosophila larval muscles. J. Neuroscience 15: 6085-6093
Gu, G.-G. and Singh, S. (1995) Pharmacological analysis of heartbeat in Drosophila. J. Neurobiology 28: 269-280
Chopra, M. and Singh, S. (1994). Developmental temperature selectively regulates a voltage-activated potassium current in Drosophila. J. Neurobiol. 25, 119-126
Singh S. (1993). Quantification of countercurrent distribution: from molecular partition to animal behavior. Biochem. Biophys. Res. Comm. 196: 430 - 434
Komatsu, A. K., Singh, S., Rathe, P. and Wu, C.-F. (1990). Mutational and gene-dosage analysis of calcium activated potassium channels in Drosophila : Correlation of micro- and macroscopic currents. Neuron 4: 313-321
Singh, S. and Wu, C.-F. (1990). Properties of potassium currents and their role in membrane excitability in Drosophila larval muscle fibers. J. Exp. Biol. 152: 59-76
Singh, S. and Wu, C.-F. (1989). Complete separation of four potassium currents in Drosophila. Neuron 2: 1325-1329.
Wu, C.-F., Tsai, M.-C., Chen, M.-L., Zhong, Y., Singh, S. and Lee, C. Y. (1989). Actions of dendrotoxin on K+ channels and neuromuscular transmission in Drosophila melanogaster and its effects in synergy with K+ channel-specific drugs and mutations. J. Exp. Biol. 147: 21-41.
Singh, S., Chopra, M. J. S., Bhandari, P. and Guha, D. (1989). Isolation of autosomal behavioral mutations in Drosophila. In 'Neurobiology of Sensory Systems', (R. N. Singh and N. J. Strausfeld, eds) Plenum Press, NY, pp 419-426.
Schlegel, P., Jen, P. H.-S. and Singh, S. (1988). Auditory spatial sensitivity of inferior collicular neurons of echolocating bats. Brain Res. 456: 127-138.
Singh, S., Bhandari, P., Chopra, M. J. S. and Guha, D. (1987). Isolation of autosomal mutations in Drosophila melanogaster without setting up lines. Molec. Gen. Genet. 208: 226-229.
Neuweiler, G., Singh, S. and Sripathi, K. (1984). Audiograms of a South Indian bat community. J. Comp. Physiol. 154: 133-142.
Schlegel, P. and Singh, S. (1983). Unmasking in neurons of the inferior colliculus of Eptesicus fuscus with binaural stimulation. Hearing Res. 10: 331-343.
Singh, S. (1983). A mutagenesis scheme for obtaining autosomal mutations in Drosophila . Ind. J. Exp. Biol. 21: 635-636.
Singh, S. and Siddiqi, O. (1981). torpid , a new sex linked temperature paralytic mutation in Drosophila melanogaster. Molec. Gen. Genet. 181: 400-402.
