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The effects of intracellular application of two novel Ca2+ releasing agents have been studied in cultured rat dorsal root ganglion (DRG) neurones by monitoring Ca(2+)-dependent currents as a physiological index of raised free cytosolic Ca2+ ([Ca2+]i). A protein based sperm factor (SF) extracted from mammalian sperm, has been found to trigger Ca2+ oscillations and to sensitize unfertilized mammalian eggs to calcium induced calcium release (CICR). In this study intracellular application of SF activated Ca(2+)-dependent currents in approximately two-thirds of DRG neurones. The SF induced activity was abolished by heat treatment, attenuated by increasing the intracellular Ca2+ buffering capacity of the cells and persisted when extracellular Ca2+ was replaced by Ba2+. In addition, activity could be triggered or potentiated by loading the cells with Ca2+ by activating a series of voltage-gated Ca2+ currents. Ca(2+)-activated inward current activity was also generated by intracellular application of cyclic ADP-ribose (cADPR), a metabolite of NAD+, which causes Ca2+ release in sea urchin eggs. This activity could also be enhanced by loading the cells with Ca2+. The cADPR induced activity, but not the SF induced activity, was abolished by depleting the caffeine sensitive Ca2+ store. Ruthenium red markedly attenuated SF induced activity but had little action on cADPR induced activity or caffeine induced activity. Our results indicate that both SF and cADPR release intracellular Ca2+ pools in DRG neurones and that they appear to act on subtly distinct stores or distinct intracellular Ca2+ release mechanisms, possibly by modulating CICR.

Original publication

DOI

10.1091/mbc.3.12.1415

Type

Journal article

Journal

Molecular biology of the cell

Publication Date

12/1992

Volume

3

Pages

1415 - 1425

Addresses

Department of Physiology, St. George's Hospital Medical School, London, UK.

Keywords

Spermatozoa, Ganglia, Spinal, Neurons, Cells, Cultured, Animals, Animals, Newborn, Swine, Rats, Rats, Wistar, Ruthenium Red, Barium, Calcium, Caffeine, Adenosine Diphosphate Ribose, Cyclic ADP-Ribose, Proteins, Calcium Channels, Tissue Extracts, Membrane Potentials, Cricetinae, Male