Intra- and intercellular calcium signaling in human SK-N-MCIXC neuroepithelioma cells.
Palmer, Roy Kyle
1995
Abstract
Rapid, transient changes in cytosolic Ca$\sp{2+}$ are known to mediate a diverse variety of cellular functions (such as contraction, secretion, growth and proliferation) in response to the presence of extracellular signaling molecules. In nonexcitable cells, the principal event responsible for mobilization of intracellular Ca$\sp{2+}$ is agonist occupancy of receptors coupled to phosphoinositide-specific phospholipase C (PIC). The activation of this enzyme results in the formation of inositol 1,4,5-trisphosphate (IP$\sb3$), a second messenger molecule that effects the release of Ca$\sp{2+}$ from the endoplasmic reticulum into the cytosol. I used digital imaging microfluorimetry to measure agonist-elicited intracellular Ca$\sp{2+}$ signals in human clonal SK-N-MCIXC neuroepithelioma cells loaded with the fluorescent Ca$\sp{2+}$-binding dye fura-2. The Ca$\sp{2+}$ signals produced by full agonists acting at different PIC-coupled receptors were clearly distinguishable with respect to their kinetics and magnitude. In addition, each agonist stimulated Ca$\sp{2+}$ signals from different numbers of cells. These findings indicate that differences in Ca$\sp{2+}$ signals may allow SK-N-MCIXC cells to distinguish extracellular stimuli received through multiple receptors coupling to the same signal transduction pathway. Some, but not all, of the diversity in the Ca$\sp{2+}$ signals could be accounted for by the intracellular concentrations of IP$\sb3$ generated by the different agonists. I then microinjected individual SK-N-MCIXC cells with IP$\sb3,$ in an attempt to examine regulation of intracellular Ca$\sp{2+}$ in the absence of cell-surface receptor stimulation. Following microinjection of IP$\sb3,$ a rise in cytosolic Ca$\sp{2+}$ was observed not only in the injected cell, but also in adjacent cells. The mediator of the intercellular propagation of the Ca$\sp{2+}$ responses appears to have been a secreted nucleotide, possibly ATP or ADP. Pharmacological evidence indicates that these may activate P$\sb{\rm2Y}$ purinergic receptors on SK-N-MCIXC cells. I conclude that activation of different PIC-linked receptors on SK-N-MCIXC cells results in Ca$\sp{2+}$ "signatures" which allow the signals from extracellular stimuli to remain distinct. Furthermore, a rise in intracellular Ca$\sp{2+}$ in SK-N-MCIXC cells results in the release of nucleotides which then activate specific P$\sb{\rm2Y}$ receptors on neighboring cells, serving to further the propagation of intercellular Ca$\sp{2+}$ signals. Nucleotides secreted as a result of high intracellular Ca$\sp{2+}$ could potentially influence the characteristics of agonist-elicited Ca$\sp{2+}$ signals, contributing to the maintenance of specificity in the PIC signal transduction cascade.Other Identifiers
(UMI)AAI9610215
Subjects
Health Sciences, Pharmacology Biology, Animal Physiology
Types
Thesis
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