Kurt A. G. Schmidt

Forskolin binding sites in rat liver and brain membranes

Using [3H]14,15-dihydroforskolin as a radioactive ligand, forskolin binding sites in rat liver and rat brain membranes were identified. Scatchard analysis of binding data revealed equilibrium dissociation constants of 1.6 microM in liver and 0.79 microM in brain membranes. The ligand could be displaced by either forskolin or dihydroforskolin. The maximal number of binding sites in liver and brain was 179 and 3.2 pmol/mg protein, respectively. The question whether these forskolin binding sites are related to the adenylate cyclase stimulating action of the diterpene remains open.

Characterization of forskolin binding sites in rat brain membranes using [14,15-3H]14,15-dihydroforskolin as a ligand.

Summary[14, 15-3H]14, 15-Dihydroforskolin ([3H]DHF) has been used as a radioactive ligand to identify forskolin binding sites in rat brain membranes. The binding was saturable and reversible. The binding sites showed positive cooperative properties as evident from an upward convex Scatchard plot and a Hill coefficient of 1.6. The equilibrium dissociation constants (KD) were in the range between 10 μM and 10 nM as estimated from the limiting slopes of the curved Scatchard plot. Half-maximal saturation of the binding sites was observed at a ligand concentration of 225 nM. The binding kinetics were very rapid: Binding equilibrium was reached in less than 2 min and a large excess of cold forskolin displaced 80% of the radioligand within 2 min. The dissociation reaction was not first order, characterized by a decreasing dissociation rate constant. Bound [3H]DHF could be displaced with forskolin (IC50 0.3 μM), 14,15-dihydroforskolin (IC50 0.8 μM) and 7-desacetylforskolin (IC50 3 μM). However, nucleotides (ATP, GTP) and other receptor ligands (adenosine, isoproterenol) had no effect on the binding. Although the density of the forskolin binding sites (3.2 pmole/mg protein) is similar to those of other adenylate cyclase linked receptors, discrepancies between the KD and the ED50 obtained in adenylate cyclase studies and the finding that activation of the enzyme by forskolin is negative cooperative makes it difficult to clearly relate the binding sites to adenylate cyclase.

Correction to “New Experimental Data and Reference Models for the Viscosity and Density of Squalane”

Squalane” Kurt A. G. Schmidt*1, Doug Pagnutti2, Meghan D. Curran3, Anil Singh4, J. P. Martin Trusler5, Geoffrey C. Maitland5, Mark McBride-Wright5 1Schlumberger, Abingdon Technology Center, Lambourn Court, Wyndyke Furlong, Abingdon, United Kingdom, OX14 1UJ 2 Schlumberger, DBR Technology Center, 9450-17 Ave, Edmonton, AB, Canada, T6N 1M9 3Department of Chemical and Materials Engineering, University of Alberta, 9107 116 Street, Edmonton, AB, Canada, T6G 2V4 4Schlumberger, Schlumberger Rosharon Campus, 14910 Airline Road, Rosharon, TX, USA, 77583 5Department of Chemical Engineering, Imperial College London, South Kensington Campus, London, United Kingdom, SW7 2AZ *Corresponding Author E-mail: kschmidt@slb.com J. Chem. Eng. Data 2015, 60 (1), 137−150. DOI:10.1021/je5008789 In Table 8 of the original paper, the parameters for the density model were labeled incorrectly. The partial table below correctly relates the parameters with their numerical values. This correction will allow readers to use the proposed density model correctly. It should be mentioned that all the results and findings reported in the original paper are valid. The authors would like to apologize for any inconvenience this may have caused. Table 8. Results of the regression analysis Density Parameter Value