NAADP-mediated channel “chatter” in neurons of the rat medulla oblongata

G. Cristina Brailoiu , Eugene Brailoiu , Raman Parkesh , Antony Galione , Grant C Churchill , Sandip Patel (1) , Nae J. Dun

1 Department of Cell and Developmental Biology

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca2+-mobilizing messenger that stimulates Ca2+ release in a variety of cells. NAADP-sensitive Ca2+ channels are thought to reside on acidic Ca2+ stores and to be functionally coupled to inositol trisphosphate and/or ryanodine receptors located on the endoplasmic reticulum. Whether NAADP-sensitive Ca2+ channels “chatter” to other channels, however, is not clear. In the present study, we have used a cell-permeant NAADP analogue to probe NAADP-mediated responses in rat medulla oblongata neurons. NAADP acetoxymethyl ester (NAADP-AM) evoked global cytosolic Ca2+ signals in isolated neurons that were reduced in amplitude by removal of external Ca2+, abolished by disruption of acidic compartments and substantially inhibited by blockade of ryanodine receptors. In rat medullary slices, NAADP-AM depolarized neurons from the nucleus ambiguus in the presence of intracellular EGTA but not of the faster Ca2+ chelator BAPTA. Depolarization was also dependent upon extracellular Ca2+, acidic stores and ryanodine receptors. In voltage-clamp mode, NAADP-AM induced an inward current with a reversal potential of approximately 0 mV. Our data reveal the presence of acidic NAADP-sensitive Ca2+ stores in medulla neurons the mobilization of which results not only in global Ca2+ signals but also in local signals that activate non-selective cation channels on the cell surface resulting in depolarization. Thus, NAADP is capable of coordinating channels both within the cell interior and at the cell membrane representing a novel mechanism for excitation of central neurons.

Mots clés: Life Sciences

G. Cristina Brailoiu, Eugene Brailoiu, Raman Parkesh, Antony Galione, Grant C Churchill, et al.. NAADP-mediated channel “chatter” in neurons of the rat medulla oblongata. Biochemical Journal, 2009, 419 (1), pp.91-97. ⟨10.1042/BJ20081138⟩. ⟨hal-00479036⟩