Dataset Information

Ca(2+)-mobilizing hormones induce sequentially ordered Ca2+ signals in multicellular systems of rat hepatocytes.

ABSTRACT: The development of hormone-mediated Ca2+ signals was analysed in polarized doublets, triplets and quadruplets of rat hepatocytes by video imaging of fura2 fluorescence. These multicellular models showed dilated bile canaliculi, and gap junctions were observed by using an anti-connexin-32 antibody. They also showed highly organized Ca2+ signals in response to vasopressin or noradrenaline. Surprisingly, the primary rises in intracellular Ca2+ concentration ([Ca2+]i) did not start randomly from any cell of the multiplet. It originated invariably in the same hepatocyte (first-responding cell), and then was propagated in a sequential manner to the nearest connected cells (cell 2, then 3, in triplets; cell 2, 3, then 4 in quadruplets). The sequential activation of the cells appeared to be an intrinsic property of multiplets of rat hepatocytes. (1) In the continued presence of hormones, the same sequential order was observed up to six times, i.e. at each train of oscillations occurring between the cells. (2) The order of [Ca2+]i responses was modified neither by the repeated addition of hormones nor by the hormonal dose. (3) The mechanical disruption of an intermediate cell slowed down the speed of the propagation, suggesting a role of gap junctions in the rapidity of the sequential activation of cells. (4) The same multiplet could have a different first-responding cell for vasopressin or noradrenaline, suggesting a role of the hormonal receptors in the sequentiality of cell responses. It is postulated that a functional heterogeneity of hormonal receptors, and the presence of functional gap junctions, are involved in the existence of sequentially ordered hormone-mediated [Ca2+]i rises in the multiplets of rat hepatocytes.

SUBMITTER: Combettes L

PROVIDER: S-EPMC1137532 | biostudies-other | 1994 Dec

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Novel CRISPR-Cas systems possess substantial potential for genome editing and manipulation of gene expression. The types and numbers of CRISPR-Cas systems vary substantially between different organisms. Some filamentous cyanobacteria harbor > 40 different putative CRISPR repeat-spacer cassettes, while the number of cas gene instances is much lower. Here we addressed the types and diversity of CRISPR-Cas systems and of CRISPR-like repeat-spacer arrays in 171 publicly available genomes of multicellular cyanobacteria. The number of 1328 repeat-spacer arrays exceeded the total of 391 encoded Cas1 proteins suggesting a tendency for fragmentation or the involvement of alternative adaptation factors. The model cyanobacterium Anabaena sp. PCC 7120 contains only three cas1 genes but hosts three Class 1, possibly one Class 2 and five orphan repeat-spacer arrays, all of which exhibit crRNA-typical expression patterns suggesting active transcription, maturation and incorporation into CRISPR complexes. The CRISPR-Cas system within the element interrupting the Anabaena sp. PCC 7120 fdxN gene, as well as analogous arrangements in other strains, occupy the genetic elements that become excised during the differentiation-related programmed site-specific recombination. This fact indicates the propensity of these elements for the integration of CRISPR-cas systems and points to a previously not recognized connection. The gene all3613 resembling a possible Class 2 effector protein is linked to a short repeat-spacer array and a single tRNA gene, similar to its homologs in other cyanobacteria. The diversity and presence of numerous CRISPR-Cas systems in DNA elements that are programmed for homologous recombination make filamentous cyanobacteria a prolific resource for their study. Abbreviations: Cas: CRISPR associated sequences; CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats; C2c: Class 2 candidate; SDR: small dispersed repeat; TSS: transcriptional start site; UTR: untranslated region.

Project description:Rat hepatocytes rapidly incorporate [32P]Pi into phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]; their monoester phosphate groups approach isotopic equilibrium with the cellular precursor pools within 1 h. Upon stimulation of these prelabelled cells with Ca2+-mobilizing stimuli (V1-vasopressin, angiotensin, alpha 1-adrenergic, ATP) there is a rapid fall in the labelling of PtdIns4P and PtdIns(4,5)P2. Pharmacological studies suggest that each of the four stimuli acts at a different population of receptors. Insulin, glucagon and prolactin do not provoke disappearance of labelled PtdIns4P and PtdIns(4,5)P2. The labelling of PtdIns4P and PtdIns(4,5)P2 in cells stimulated with vasopressin or angiotensin initially declines at a rate of 0.5-1.0% per s, reaches a minimum after 1-2 min and then returns towards the initial value. The dose-response curves for the vasopressin- and angiotensin-stimulated responses lie close to the respective receptor occupation curves, rather than at the lower hormone concentrations needed to evoke activation of glycogen phosphorylase. Disappearance of labelled PtdIns4P and PtdIns(4,5)P2 is not observed when cells are incubated with the ionophore A23187. The hormone-stimulated polyphosphoinositide disappearance is reduced, but not abolished, in Ca2+-depleted cells. These hormonal effects are not modified by 8-bromo cyclic GMP, cycloheximide or delta-hexachlorocyclohexane. The absolute rate of polyphosphoinositide breakdown in stimulated cells is similar to the rate previously reported for the disappearance of phosphatidylinositol [Kirk, Michell & Hems (1981) Biochem. J. 194, 155-165]. It seems likely that these changes in polyphosphoinositide labelling are caused by hormonal activation of the breakdown of PtdIns(4,5)P2 (and may be also PtdIns4P) by the action of a polyphosphoinositide phosphodiesterase. We therefore suggest that the initial response to hormones is breakdown of PtdIns(4,5)P2 (and PtdIns4P?), and that the simultaneous disappearance of phosphatidylinositol might be a result of its consumption for the continuing synthesis of polyphosphoinositides.

Dataset Information

Ca(2+)-mobilizing hormones induce sequentially ordered Ca2+ signals in multicellular systems of rat hepatocytes.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets