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Intracellular calcium signaling in nucleotide stimulated porcine aortic smooth muscle cells
Abstract
Individual smooth muscle cells respond in a dose dependent manner to extracellular ATP with an immediate initial transient rise followed by oscillations in (Ca$\sp{2+}$) $\sb{\rm i}$ that are asynchronous from cell to cell. There is convincing pharmacological evidence that two receptors, the putative P$\sb{\rm 2u}$ and P$\sb{\rm 2g}$ nucleotide receptors mediate the cellular response to extracellular nucleotides. At low ATP concentrations, cells initially respond with a measurable lag time that is a function of ligand concentration. Electrophysiological experiments also provide evidence that ATP produces an initial transient and oscillations of Cl$\sp-$ inward current with a time course similar to the (Ca$\sp{2+}$) $\sb{\rm i}$ transient and oscillations. This Cl$\sp-$ current is activated only in the presence of both receptor occupation and a (Ca$\sp{2+}$) $\sb{\rm i}$ rise. While the initial transient rise in (Ca$\sp{2+}$) $\sb{\rm i}$ rapidly desensitizes, the subsequent oscillations can persist in the continued presence of extracellular ATP and Ca$\sp{2+}$. Further evidence indicates that the oscillations are controlled by a different mechanism than the initial transient. First, the EC$\sb{50}$ for the oscillations is 20 fold higher than that for the initial transient (2.6 and O.11 $\mu$M, respectively). Second, the initial transient appears to have access to a separate intracellular Ca$\sp{2+}$ pool from the one shared by both phenomena. The (Ca$\sp{2+}$) $\sb{\rm i}$ oscillations are shown to be spatially nonuniform, with (Ca$\sp{2+}$) $\sb{\rm i}$ propagating from multiple initiation sites as both cytoplasmic (Ca$\sp{2+}$) $\sb{\rm i}$ waves and gradients. Furthermore, an individual cell can display separate oscillations of discrete frequencies that draw upon Ca$\sp{2+}$ pools that are independently regulated. Adenosine, a metabolite of ATP, increases the fraction of cells that oscillate without an initial transient. ATP stimulates a rise in arachidonic acid production and secretion in a time- and dose-dependent manner. Pretreatment with indomethacin, an inhibitor of PGE$\sb2$ production from arachidonic acid (AA), abolished the ATP-mediated oscillations. Forskolin, an activator of adenylyl cyclase which causes a rise in cellular (cAMP), supports oscillations in ATP-stimulated cells that have previously responded with an initial transient followed by a high noisy plateau. These findings indicate that (Ca$\sp{2+}$) $\sb{\rm i}$ oscillations are regulated by the cAMP second messenger signal cascade.
Subject Area
Cellular biology|Biophysics|Physiology
Recommended Citation
Mahoney, My Georgia, "Intracellular calcium signaling in nucleotide stimulated porcine aortic smooth muscle cells" (1993). Doctoral Dissertations Available from Proquest. AAI9329641.
https://scholarworks.umass.edu/dissertations/AAI9329641