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  • 1
    Electronic Resource
    Electronic Resource
    Ca2+/Calmodulin Distinguishes Between Guanyl-5′-yl-Imidodiphosphate-and Opiate-Mediated Inhibition of Rat Striatal Adenylate Cyclase (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 49 (1987), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The inhibition of adenylate cyclase from rat striatal plasma membranes by guanyl-5′-yl-imidodiphos-phate [Gpp(NH)p] and morphine was compared to determine whether Gpp(NH)p-mediated inhibition accurately reflected hormone-mediated inhibition in this system. Inhibition of adenylate cyclase activity by Gpp(NH)p and morphine was examined with respect to temperature, divalent cation concentration, and the presence of Ca2+/calmodulin (Ca2+/CaM). Gpp(NH)p-mediated inhibition was dependent on the presence of Ca2+/CaM at 24°C; the inhibition was independent of Ca2+/CaM at 18°C; and inhibition could not be detected in the presence, or absence, of Ca2+/ CaM at 30°C. In contrast, naloxone-reversible, morphine-induced inhibition of adenylate cyclase was independent of both temperature and the presence of Ca2+/CaM. Mg2+dose-response curves also reinforced the differences in the Ca2+/CaM requirement for Gpp(NH)p-and morphine-induced inhibition. Because Gpp(NH)p-mediated inhibition was independent of Ca2+/CaM at low basal activities (i.e., 18°C, or below 1 mM Mg2+) and dependent on the presence of Ca2+/CaM at higher basal activities (24°C, or above 1 mM Mg2+), the inhibitory effects of Gpp(NH)p were examined at 1 mM Mg2+ in the presence of 100 nM forskolin. Under these conditions, both Gpp(NH)p-and morphine-induced inhibition of adenylate cyclase were independent of Ca2+/CaM. The results demonstrate that the requirement for Ca2+/CaM to observe Gpp(NH)p-mediated inhibition depends on the basal activity of adenylate cyclase, whereas hormone-mediated inhibition is Ca2+/CaM independent under all conditions. Further, this study shows that, under certain conditions, Gpp(NH)p-mediated inhibition of adenylate cyclase does not mimic the inhibition of adenylate cyclase produced by a complete interaction between the inhibitory hormone receptor, the guanine nucleotide-regulatory component that mediates inhibition, and the catalytic unit of the adenylate cyclase complex in striatal plasma membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1987.tb10025.x
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  • 2
    Electronic Resource
    Electronic Resource
    Interaction of the Inhibitory GTP Regulatory Component with Soluble Cerebral Cortical Adenylate Cyclase (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 46 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Functional interaction of the inhibitory GTP regulatory component (Ni) with the adenylate cyclase catalytic subunit has not previously been demonstrated after detergent solubilization. The present report describes a sodium cholate-solubilized preparation of rat cerebral cortical membrane adenylate cyclase that retains guanine nucleotide-mediated inhibition of activity. Methods of membrane preparation, cholate extraction, and assay conditions were manipulated such that guanosine-5′-(β-γ-imido)triphosphate [Gpp(NH)p] inhibited basal activity 40–60%. The rank order of potency among various GTP analogs was similar in cholate extracts and in membranes: guanosine-5′-0-(3-thiotriphosphate) 〉 Gpp(NH)p 〉 GTP. Inclusion of 0.1 mM EGTA reduced basal activity 70–90% and abolished Gpp(NH)p inhibition of basal activity in both membranes and cholate extracts. Forskolin-stimulated activity was also inhibited by Gpp(NH)p. Treatment of either membranes or cholate extracts with N-ethylmaleimide abolished Gpp(NH)p inhibition. Gel filtration of the cholate extract over a Sepharose 6B column in 0.1% Lubrol PX partially resolved the adenylate cyclase components. However, Gpp(NH)p inhibitin of basal activity (60% of the control) was maintained in select column fractions. Sucrose gradient centrifugation totally resolved the catalytic subunit from both functional Ni and stimulatory GTP regulatory component (Ns) activities. The sedimentation of functional Ni activity was detected by assaying the ability of sucrose gradient fractions to confer Gpp(NH)p inhibition of the resolved catalytic activity. Labeling of gradient or column fractions with pertussis toxin and [32P]NAD revealed that both the 39,000- and 41,000-dalton substrates comigrated with the functional Ni activity. These results demonstrate the feasibility of reconstituting Ni inhibition with resolved catalytic activity directly in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb01769.x
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  • 3
    Electronic Resource
    Electronic Resource
    Distinct interactions between Ca2+/calmodulin and neurotransmitter stimulation of adenylate cyclase in striatum and hippocampus (1988)
    Springer
    Cellular and molecular neurobiology 8 (1988), S. 459-469 
    Details
    ISSN: 1573-6830
    Keywords: calmodulin ; adenylate cyclase ; hippocampus ; striatum ; dopamine ; vasoactive intestinal peptide (VIP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Ca2+ and cAMP both act as intracellular second messengers of receptor activation. In neuronal tissue, Ca2+ acting via calmodulin can elevate cAMP levels. This regulation by Ca2+ provides a means whereby the elevation of intracellular [Ca2+] might modulate cAMP generation. 2. In the present studies, the impact of the Ca2+/calmodulin regulation on receptor-mediated stimulation of activity is compared in striatum and hippocampus—regions of differing sensitivity to Ca2+/camodulin. Ca2+/calmodulin stimulated striatal and hippocampal adenylate cyclase activity by 1.4-and 2.7-fold respectively, while dopamine and vasoactive intestinal peptide (VIP) stimulated the enzyme activity of these respective regions by 1.3- and 2-fold. 3. In the presence of Ca2+/calmodulin, the dopamine dose-response curve in the striatum was shifted upward, without alteration of the slope of the curve or of the maximal stimulation of activity elicited by dopamine. In the hippocampus, the ability of VIP to stimulate adenylate cyclase activity was reduced by the presence of calmodulin. 4. The dose dependence of these actions of calmodulin was examined. In the striatum, the stimulation of adenylate cyclase activity by 0.1 to 0.3µM calmodulin obscured dopamine stimulation, while 1 to 10µM was additive with the dopamine stimulation. In the hippocampus, all concentrations of calmodulin (0.1 to 10µM) reduced VIP-mediated stimulation of enzyme activity. 5. These data suggest that the ratio of calmodulin-sensitive to calmodulin-insensitive adenylate cyclase activity varies in different rat brain regions and that, in those regions in which this ratio is low (e.g., rat striatum and most peripheral systems), calmodulin- and receptor-mediated activation of adenylate cyclase activity will be additive, while in those systems in which this ratio is high (e.g., most of the central nervous system), calmodulin will reduce receptor-mediated stimulation of enzyme activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00711229
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  • 4
    Electronic Resource
    Electronic Resource
    Calmodulin plays a dominant role in determining neurotransmitter regulation of neuronal adenylate cyclase (1988)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 36 (1988), S. 417-427 
    Details
    ISSN: 0730-2312
    Keywords: rat brain ; hormones ; calcium ; cAMP ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Ca2+, through the mediation of calmodulin, stimulates the activity of brain adenylate cyclase. The growing awareness that fluctuating Ca2+, concentrations play a major role in intracellular signalling prompted the present study, which aimed to investigate the implications for neurotransmitter (receptor) regulation of enzymatic activity of this calmodulin regulation. The role of Ca2+/calmodulin in regulating neurotransmitter-mediated inhibition and stimulation was assessed in a number of rat brain areas. Ca2+/calmodulin stimulated adenylate cyclase activity in EGTA-washed plasma preparations from each region studied - from 1.3-fold (in striatum) to 3.4-fold (in cerebral cortex). The fold-stimulation produced by Ca2+/calmodulin was decreased in the presence of GTP, forskolin, or Mn2+. In EGTA-washed membranes, receptor-mediated inhibition of adenylate cyclase was strictly dependent upon Ca2+/calmodulin stimulation in all regions, except striatum. A requirement for Mg2+ in combination with Ca2+/calmodulin to observe neurotransmitter-mediated inhibition was also observed. In contrast, receptor-mediated stimulation of activity was much greater in the absence of Ca2+/calmodulin. The findings demonstrate that ambient Ca2+ concentrations, in concert with endogenous calmodulin, may play a central role in dictating whether inhibition or stimulation of adenylate cyclase by neurotransmitters may proceed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240360410
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