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  • 1
    ISSN: 1432-2013
    Keywords: Key words Calcium channels ; α2-Adrenoceptors ; G proteins ; Dexmedetomidine ; PC-12 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The ability of recombinant rat α2D-and α2B-adrenoceptors expressed in nerve-growth-factor-differentiated pheochromocytoma PC-12 cells to modulate Ca2+ currents, recorded by the whole-cell patch-clamp technique, has been studied. Ca2+ currents in different cells were either reversibly reduced or increased by dexmedetomidine, an α2-adrenergic agonist, in a concentration-dependent manner. Pertussis toxin pretreatment reduced the number of cells that showed an inhibitory response and reduced the magnitude of inhibition. In cells expressing the α2B-adrenoceptor, pertussis toxin increased the proportion of cells from which a stimulatory effect on Ca2+ currents could be recorded. The magnitude of the inhibitory responses was unaffected but the stimulatory responses were considerably reduced by the dihydropyridine Ca2+ channel blocker nifedipine (5 μM). All effects of dexmedetomidine were reversible upon wash-out and inhibited by the antagonist rauwolscine. The results support the idea that modulation of voltage-dependent Ca2+ channels in transfected PC-12 cells is mediated by activation of recombinant α2D- and α2B-adrenoceptors. This receptor activation predominantly causes inhibition of dihydropyridine-insensitive Ca2+ channels via pertussis-toxin-sensitive G proteins. Additionally receptor activation can also lead to stimulation of dihydropyridine-sensitive Ca2+ channels via pertussis-toxin-insensitive mechanisms.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0878
    Keywords: Carotid body ; Glomus cells ; Endocytosis ; Cationized ferritin ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Glomus cells from carotid bodies of adult rats dissociated by means of collagenase or collagenase + trypsin were used to study by electron microscopy the endocytotic uptake of cationized ferritin (CF) tracer into subcellular compartments. The glomus cells were incubated with the tracer (1) in a basic salt medium (BM), or (2) in the BM into which calcium ionophore A23187 had been added, or (3) in a potassium-rich medium. Incubation of the cells in BM containing CF for 30 min resulted in attachment of the tracer to the cell membrane and uptake of a few solitary tracer particles into small vesicles and multivesicular bodies. No uptake into the cisternae of the Golgi apparatus was observed. Further incubation in BM containing CF for another 30 min resulted in increased uptake of the tracer into small vesicles and multivesicular bodies. A similar pattern of uptake was observed when the dissociated glomus cells were first preincubated in BM with CF for 30 min and then incubated for 1 min or 30 min in the BM solution containing both the ionophore and CF. Upon such incubation, CF particles were seen to penetrate into coated pits and sites of exocytosis at the cell surface. When the 30-min preincubation in BM was followed by incubation in a CF-containing potassium-rich medium for 15–30 min, uptake into vesicles, small lysosomes and occasionally also into profiles of the smooth endoplasmic reticulum was seen. Endocytotic mechanisms of the glomus cells are outlined.
    Type of Medium: Electronic Resource
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