Palmer_1994_J.Neurochem_63_2099

Fura-2 digital imaging microfluorimetry was used to evaluate the Ca2+ 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 (Ca2+i) but of different magnitudes (ET-1 = ATP > Oxo-M > NE). The Ca2+ 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 Ca2+ influx. The Ca2+ 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 Ca2+ signal, which was characteristic of the response to Oxo-M, was observed in < 40% of cells stimulated with ET-1 and absent from Ca2+ signals elicited after NE addition. Removal of extracellular Ca2+ enhanced the rate of decay of Ca2+ signals generated by ATP, ET-1, or Oxo-M and, when evident, abolished the sustained phase of Ca2+ influx. In the absence of extracellular Ca2+, NE elicited asynchronous multiple Ca2+ transients. In either the absence or presence of extracellular Ca2+-, > 94% of cells responded to ET-1 or ATP, whereas corresponding values for Oxo-M and NE were approximately 74 and approximately 48%.(ABSTRACT TRUNCATED AT 250 WORDS)