title: Differential Regulation of Multiple Steps in Inositol 1,4,5-Trisphosphate Signaling by Protein Kinase C Shapes Hormone-stimulated Ca2+ Oscillations.
abstract: How Ca(2+) oscillations are generated and fine-tuned to yield versatile downstream responses remains to be elucidated. In hepatocytes, G protein-coupled receptor-linked Ca(2+) oscillations report signal strength via frequency, whereas Ca(2+) spike amplitude and wave velocity remain constant. IP3 uncaging also triggers oscillatory Ca(2+) release, but, in contrast to hormones, Ca(2+) spike amplitude, width, and wave velocity were dependent on [IP3] and were not perturbed by phospholipase C (PLC) inhibition. These data indicate that oscillations elicited by IP3 uncaging are driven by the biphasic regulation of the IP3 receptor by Ca(2+), and, unlike hormone-dependent responses, do not require PLC. Removal of extracellular Ca(2+) did not perturb Ca(2+) oscillations elicited by IP3 uncaging, indicating that reloading of endoplasmic reticulum stores via plasma membrane Ca(2+) influx does not entrain the signal. Activation and inhibition of PKC attenuated hormone-induced Ca(2+) oscillations but had no effect on Ca(2+) increases induced by uncaging IP3. Importantly, PKC activation and inhibition differentially affected Ca(2+) spike frequencies and kinetics. PKC activation amplifies negative feedback loops at the level of G protein-coupled receptor PLC activity and/or IP3 metabolism to attenuate IP3 levels and suppress the generation of Ca(2+) oscillations. Inhibition of PKC relieves negative feedback regulation of IP3 accumulation and, thereby, shifts Ca(2+) oscillations toward sustained responses or dramatically prolonged spikes. PKC down-regulation attenuates phenylephrine-induced Ca(2+) wave velocity, whereas responses to IP3 uncaging are enhanced. The ability to assess Ca(2+) responses in the absence of PLC activity indicates that IP3 receptor modulation by PKC regulates Ca(2+) release and wave velocity.
authors.affiliation: From the Department of Pharmacology and Physiology, New Jersey Medical School Rutgers, The State University of New Jersey, Newark, New Jersey 07103.
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Bartlett
authors.affiliation: From the Department of Pharmacology and Physiology, New Jersey Medical School Rutgers, The State University of New Jersey, Newark, New Jersey 07103.
authors.forename: Walson
authors.initials: W
authors.lastname: Metzger
authors.affiliation: From the Department of Pharmacology and Physiology, New Jersey Medical School Rutgers, The State University of New Jersey, Newark, New Jersey 07103.
authors.forename: Lawrence D
authors.initials: LD
authors.lastname: Gaspers
authors.affiliation: From the Department of Pharmacology and Physiology, New Jersey Medical School Rutgers, The State University of New Jersey, Newark, New Jersey 07103 andrew.thomas@rutgers.edu.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Thomas
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006728:Hormones / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007294:Inositol / Q000737:chemistry / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000737:chemistry / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000235:genetics / Q000378:metabolism*; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction
chemical_list: D006728:Hormones; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007294:Inositol; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D002118:Calcium
keywords: PKC; calcium; calcium intracellular release; calcium oscillations; hepatocyte; inositol 1,4,5-trisphosphate (IP3); inositol trisphosphate receptor (IP3R)