Premium
Agonist‐Specific Calcium Signaling and Phosphoinositide Hydrolysis in Human SK‐N‐MCIXC Neuroepithelioma Cells
Author(s) -
Palmer R. Kyle,
Yule David I.,
McEwen Edward L.,
Williams John A.,
Fisher Stephen K.
Publication year - 1994
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1994.63062099.x
Subject(s) - extracellular , biophysics , chemistry , cytosol , calcium , calcium signaling , fura 2 , agonist , endocrinology , medicine , intracellular , biochemistry , biology , receptor , enzyme
Fura‐2 digital imaging microfluorimetry was used to evaluate the Ca 2+ signals generated in single clonal human neuroepithelioma cells (SK‐N‐MCIXC) in response to agonists that stimulate phosphoinositide hydrolysis. Addition of optimal concentrations of either endothelin‐1 (ET‐1), ATP, oxotremorine‐M (Oxo‐M), or norepinephrine (NE) all resulted in an increase in the concentration of cytosolic calcium (Ca 2+ i ) but of different magnitudes (ET‐1 = ATP> NE). The Ca 2+ signals elicited by the individual agonists also differed from each other in terms of their latency of onset, rate of rise and decay, and prevalence of a sustained phase of Ca 2+ influx. The Ca 2+ signals that occurred in response to ATP had a shorter latency and more rapid rates of rise and decay than those observed for the other three agonists. Furthermore, a sustained plateau phase of the Ca 2+ signal, which was characteristic of the response to Oxo‐M, was observed in <40% of cells stimulated with ET‐1 and absent from Ca 2+ signals elicited after NE addition. Removal of extracellular Ca 2+ enhanced the rate of decay of Ca 2+ signals generated by ATP, ET‐1, or Oxo‐M and, when evident, abolished the sustained phase of Ca 2+ influx. In the absence of extracellular Ca 2+ , NE elicited asynchronous multiple Ca 2+ transients. In either the absence or presence of extracellular Ca 2+ ,>94% of cells responded to ET‐1 or ATP, whereas corresponding values for Oxo‐M and NE were ∼74 and ∼48%. Sequential addition of agonists to cells maintained in a Ca 2+ ‐free buffer indicated that each ligand mobilized Ca 2+ from a common intracellular pool. When monitored as a release of a total inositol phosphate fraction, all four agonists elicited similar (four‐ to sixfold) increases in phosphoinositide hydrolysis. However, the addition of ET‐1 or ATP resulted in larger increases in the net formation of inositol 1,4,5‐trisphosphate than did either Oxo‐M or NE. These results indicate that, in SK‐N‐MCIXC cells, the characteristics of both Ca 2+ signaling and inositol phosphate production are agonist specific.