Hypoxia inhibits the synthesis of phosphoinositides in the rabbit carotid body
Departamento de Bioquímica y Biologia Molecular y Fisiología, Instituto de Biología y Génetica Molecular (IBGM) CSIC, Facultad de Medicina, Universidad de Valladolid, E-47005 Valladolid, Spain.Pflügers Archiv - European Journal of Physiology (Impact Factor: 4.1). 06/1999; 437(6):839-45. DOI: 10.1007/s004240050853
Hypoxic transduction in the carotid body (CB) is regulated by several systems of second messengers, but the role of the phospholipase C system has not been studied. The aim of the present study was to characterize the turnover rate of inositol phosphates (InsPs) and phosphoinositides (PIs) and their modifications by hypoxia in the rabbit CB in vitro. In CBs, in which the PIs had been labelled previously with 3H-myo-inositol, hypoxia in the presence of LiCl did not modify the accumulation of 3H-InsPs, whilst exposure to hypoxia during the loading period in the presence of LiCl reduced the accumulation of 3H-InsPs by more than 50%. Endogenous levels of inositol 1,4,5-trisphosphate were unaltered by hypoxia. Synthesis of 3H-PIs from 3H-myo-inositol was markedly inhibited by hypoxia in the CB, but not in the rat superior cervical ganglion used as control tissue. Levels of 3H-phosphatidylinositol (3H-PtdIns), 3H-phosphatidylinositol 4-monophosphate and 3H-phosphatidylinositol 4,5-bisphosphate were similarly decreased, indicating that inhibition occurs at a step prior to PtdIns synthesis. It is concluded that the phospholipase C system of second messengers does not play a significant role in the short-term regulation of hypoxic transduction cascade. It can be speculated that the decrease in PI availability produced by hypoxia might be involved in the functional changes observed in the CB on chronic hypoxic exposure.
- [Show abstract] [Hide abstract]
ABSTRACT: The present study evaluated the effects of endothelin (ET) peptides on carotid sinus nerve (CSN) activity, catecholamine (CA) release, and second messenger signaling pathways in rabbit carotid bodies superfused in vitro, and in dissociated chemosensory type I cells. ET-1 (1.0 microM) and ET-3 (1.0 microM) did not alter basal CSN activity and CA release, but they potentiated nerve activity (P<0. 05) and CA release (P<0.05) evoked by hypoxia. Under basal conditions, ET-1 and ET-3 (1.0 microM each) elevated tissue cyclic AMP (cAMP) levels nearly 3-fold (P<0.001, ET-1; P<0.05, ET-3) and inositol phosphate (IP(n)) levels nearly 4-fold (P<0.01, ET-1). Hypoxia evoked an increase in carotid body cAMP, and this response was also potentiated in the presence of 1.0 microM ET-1 (P<0.01) or 1.0 microM ET-3 (P<0.001). Patch-clamp studies of isolated type I cells showed that 100 nM ET-1 elevated the peak amplitude of voltage-sensitive (L-type) Ca(2+)-currents by an average of 37.6% (P<0.001). Fluorescent Ca(2+)-imaging revealed that 100 nM ET-1 did not alter [Ca(2+)](i) under basal conditions, but that [Ca(2+)](i)-responses evoked by hypoxia were potentiated by 87% (P<0. 01). Our data indicate that ET augments chemoreceptor responses by activating second messenger signaling pathways which promote the phosphorylation of Ca(2+)-channel protein, thereby enhancing stimulus-evoked intracellular Ca(2+) levels.Respiration Physiology 06/2000; 121(1):13-23. DOI:10.1016/S0034-5687(00)00113-4
- [Show abstract] [Hide abstract]
ABSTRACT: The presence, subcellular distribution, species specificity and possible hypoxic stimulus-induced translocation of classical protein kinase C (cPKC) isozymes were examined in the carotid body. Carotid bodies were dissected from cats exposed in vivo to normoxic or acute hypoxic conditions and from normoxic rats. For immunohistochemistry isoform-specific monoclonal antisera to PKCalpha, PKCbetaI, PKCbetaII and PKCgamma were used. The immunoreactivity was visualized by fluorescein isothiocyanate (FITC) labelling. FITC/Texas red double-labelled specimens for the cPKC isozymes/tyrosine hydroxylase were used to demonstrate the chemoreceptor cell localization of cPKC isozymes. The immunofluorescence was detected using laser scanning confocal image technology. The results showed expression of the PKCalpha and PKCgamma but not PKCbeta isoforms in the cytoplasm of carotid body chemoreceptor cells. The double labelling provided evidence for the chemoreceptor cell localization of the cPKC isoforms detected. The immunostaining was most intense in the periphery of the perikarya, the nuclear envelope and, occasionally, the nucleoplasm. No major differences were found in the immunolocalization of PKCalpha and PKCgamma under normoxic and hypoxic conditions or between species. However, the immunoreactivity tended to accumulate more in the peripheral cytoplasm and away from the nucleus in the hypoxic chemoreceptor cell. This study demonstrates the presence of classical protein kinase C enzymes in chemoreceptor cells. The intensity of the immunoreactivity may suggest a role for the classical protein kinase C signalling pathway in shaping the hypoxic response at the carotid body. However, this study failed to provide firm evidence of this.European Respiratory Journal 10/2000; 16(3):459-63. DOI:10.1034/j.1399-3003.2000.016003459.x · 7.64 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Endothelin-1 (ET-1) excites carotid body (CB) chemoreceptors and induces mitosis of the chemoreceptors in chronic hypoxia. The aim of the present study was to examine the hypothesis that up-regulation of both ETA receptor and endogenous ET-1 expression in CB chemoreceptors enhances the response of intracellular Ca2+ to ET-1 following adaptation to chronic hypoxia (10% inspired O2 for 3-4 weeks). Cytosolic free [Ca2+] ([Ca2+]i) in type-I (glomus) cells freshly dissociated from rat CBs was measured by spectrofluorometry. Application of exogenous ET-1 (1-100 nM) concentration-dependently elevated [Ca2+]i in the glomus cells. This response to ET-1 (100 nM) was 49% greater in the chronically hypoxic (CH) group. The ET-1 response was abolished completely by the ETA receptor antagonist BQ610 (1 microM), but not by the ETB antagonist BQ788 (1 microM). The transient [Ca2+]i elevation induced by caffeine (30 mM) in the normoxic group was similar to that in the CH group, suggesting no differences in the intracellular Ca2+ stores. In situ hybridization with a digoxigenin-labelled antisense ETA receptor mRNA oligonucleotide probe revealed very intense and ubiquitous specific expression of ETA receptors in the lobules of glomus cells in the CH group, whereas staining in normoxic controls was light. Immunohistochemical studies revealed intense cytoplasmic staining for ET-1-immunoreactivity in most of the cell clusters in glomera in the CBs of CH rats but was faint in normoxic CBs. These findings indicate increased expression of both the ETA receptor and ET-1 in CB chemoreceptors during chronic hypoxia. Taken together, our results suggest that the [Ca2+]i response to ET-1 in rat CB chemoreceptors is augmented by up-regulation of ETA receptors and ET-1 expression. The enhancement of the paracrine/autocrine effect of ET-1 on the chemoreceptors is consistent with an excitatory and mitogenic role of the ET-1 and ETA receptor in the CB during chronic hypoxia.Pflügers Archiv - European Journal of Physiology 03/2002; 443(4):565-73. DOI:10.1007/s00424-001-0728-2 · 4.10 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.