Short-term incubation of cardiac myocytes with isoprenaline has no effect on heparin-releasable or cellular lipoprotein lipase activity.

Heparin (5 units/ml) produced a rapid (5-10 min) release of lipoprotein lipase (LPL) into the incubation medium of cardiac myocytes. Preincubation of myocytes for 30 min with 0.01-10 microM-isoprenaline, 100 microM-forskolin or 500 microM-8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate did not increase heparin-releasable LPL activity. Incubation with isoprenaline also did not change cellular LPL activity, even though the catecholamine did increase the phosphorylase a activity ratio.     

Microtubule assembly in cultivated Greene melanoma cells is stimulated by dibutyryl adenosine 3'':5''-cyclic monophosphate or cholera toxin

Both dibutyryl cyclic AMP (DBcAMP) and cholera toxin promote the formation and elongation of processes of cultivated Greene hamster melanoma cells. The formation and maintenance of these processes, which contain many microtubules, are sensitive to colcemid and vinblastine. Tubulin was measured by [3H]colchicine binding and by acrylamide gel electrophoresis. We found that DBcAMP or cholera toxin increases the ratio of polymerized to unpolymerized tubulin but not the total amount of tubulin per cell. The sum of the lengths of microtubules per unit area was significantly greater in cells treated with DBcAMP than in control cells. Our findings support the hypothesis that cyclic AMP promotes the elongation of cell processes by stimulating the assembly of microtubules from existing tubulin.     

Testosterone and 6-N,2''-O-dibutyryladenosine 3'':5''-cyclic monophosphate stimulate protein and lysosomal enzyme secretion in rat seminal vesicle.

Rat seminal-vesicle secretion was studied in vitro in a slice-incubation system. Seminal-vesicle slices were preincubated with 32Pi for 15 min, rinsed, and incubated in an isotope-free 'chase' medium for up to 4h. Gland slices spontaneously discharged protein, three lysosomal hydrolases and trichloroacetic acid-insoluble 32P into the medium in a time- and temperature-dependent manner. Testosterone (10 muM) and dibutyryl cyclic AMP (1 mM) stimulated the discharge of protein, acid hydrolases and trichloroacetic acid-insoluble 32P, and also stimulated the incorporation of 32Pi into trichloroacetic acid-insoluble components. The acid phosphatase and beta-N-acetylhexosaminidase isoenzymes were separated by isoelectric focusing. These hydrolases were secreted into the medium as acidic isoenzymes, presumably contained within primary lysosomes, whereas they occurred largely as less acidic and basic isoenzymes in the glandular tissue.     

Diffusion coefficient of the cyclic GMP analog 8-(fluoresceinyl)thioguanosine 3'',5'' cyclic monophosphate in the salamander rod outer segment.

Cyclic GMP (cGMP) is the intracellular messenger mediating phototransduction in retinal rods, with its longitudinal diffusion in the rod outer segment (ROS) likely to be a factor in determining light sensitivity. From the kinetics of cGMP-activated currents in the truncated ROS of the salamander (Ambystoma tigrinum), the cGMP diffusion coefficient was previously estimated to be approximately 60 x 10(-8) cm2 s-1. On the other hand, fluorescence measurements in intact salamander ROS using 8-(fluoresceinyl)thioguanosine 3',5'-cyclic monophosphate (Fl-cGMP) led to a diffusion coefficient for this compound of 1 x 10(-8) cm2 s-1; after corrections for differences in size and in binding to cellular components between cGMP and Fl-cGMP, this gave an upper limit of 11 x 10(-8) cm2 s-1 for the cGMP diffusion coefficient. To properly compare the two sets of measurements, we have examined the diffusion of Fl-cGMP in the truncated ROS. From the kinetics of Fl-cGMP-activated currents, we have obtained a diffusion coefficient of 3 x 10(-8) cm2 s-1 for this analog; the cGMP diffusion coefficient measured from the same truncated ROSs was approximately 80 x 10(-8) cm2 s-1. Thus, a factor of 27 appears appropriate for correcting differences in size and intracellular binding between cGMP and Fl-cGMP. Application of this correction factor to the Fl-cGMP diffusion coefficient measurements by Olson and Pugh (1993) gives a cGMP diffusion coefficient of approximately 30 x 10(-8) cm2 s-1, in reasonable agreement with the value measured from the truncated ROS.     

Treatment of intact striatal neurones with cholera toxin or 8-bromoadenosine 3',5'-(cyclic)phosphate decreases the ability of pertussis toxin to ADP-ribosylate the alpha-subunits of inhibitory and other guanine-nucleotide-binding regulatory proteins, Gi and Go. Evidence for two distinct mechanisms.

Using primary cultures of striatal neurones from the mouse embryo, we showed that treatment of intact cells with cholera toxin (5 micrograms/ml, 22 h) decreases the subsequent ADP-ribosylation of the alpha subunit of the guanine-nucleotide-binding regulatory protein Go (Go alpha) and the alpha subunit of the inhibitory guanine-nucleotide-binding regulatory protein (Gi alpha) of adenylate cyclase, which is catalyzed in vitro on neuronal membranes by pertussis toxin. The inhibitory effect of cholera toxin could not only be attributed to an increased production of cAMP in neurones. Treatment of cells with 0.1 microM 8-bromoadenosine 3',5'-(cyclic)phosphate (BrcAMP) for 16 h, or with 0.1 mM BrcAMP for 5 min, mimicked the effect of cholera toxin on the ADP-ribosylation of Go alpha and Gi alpha in vitro. However, the two agents seem to act through distinct mechanisms. The protein kinase inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine prevented the action of Br8cAMP but not that of cholera toxin. In addition, measurements of the pI of the Go alpha deduced from immunoblots of two-dimensional gels performed using a specific antibody directed against Go alpha suggest that treatment of neurones with cholera toxin induces ADP-ribosylation of Go alpha in intact cells, while BrcAMP does not.