No abstract

No abstract

Insulin and hepatocyte growth factor (HGF) induced morphologically different membrane rufflings in KB cells. Insulin-induced membrane ruffling was inhibited by microinjection of rho GDI, an inhibitory GDP/GTP exchange regulator for both rho p21 and rac p21 small GTP-binding proteins, but not inhibited by microinjection of botulinum exoenzyme C3, known to selectively ADP-ribosylate rho p21 and to impair its function. This rho GDI action was prevented by comicroinjection with guanosine 5'-(3-O-thio)triphosphate (GTP gamma S)-bound rac1 p21. In contrast, HGF-induced membrane ruffling was inhibited by microinjection of rho GDI or C3. This rho GDI action was prevented by comicroinjection with GTP gamma S-bound rhoA p21, and this C3 action was prevented by comicroinjection with GTP gamma S-bound rhoAIle-41 p21, which is resistant to C3. Microinjection of either GTP gamma S-bound rac1 p21 or rhoA p21 alone induced membrane ruffling in the absence of the growth factors. The rac1 p21-induced membrane ruffling was morphologically similar to the insulin-induced kind, whereas rhoA p21-induced ruffling was apparently different from both the insulin- and HGF-induced kinds. Membrane ruffling was also induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C-activating phorbol ester, but not by Ca2+ ionophore or microinjection of a dominant active Ki-ras p21 mutant (Ki-rasVal-12 p21). The phorbol ester-induced membrane ruffling was morphologically similar to the rhoA p21-induced kind and inhibited by microinjection of rho GDI or C3. These results indicate that rac p21 and rho GDI are involved in insulin-induced membrane ruffling and that rho p21 and rho GDI are involved in HGF- and phorbol ester-induced membrane rufflings.

Cross-flow boiling in horizontal tube bundles occurs in kettle type evaporators. Convective heat transfer due to the motion of vapor bubbles is an important factor for boiling heat transfer in the evaporator under low heat flux conditions. To clarify the liquid agitation effect on heat transfer, the local heat transfer around a tube in in-line and staggered tube bundles was investigated in two-phase flows under adiabatic and atmospheric pressure conditions. Air and tap water were used as the working fluids. The test section was a vertical duct with inner dimensions of 90 × 90 mm 2 . In-line and staggered tube bundles each containing eight rows and five columns, were used as test sections. For both bundles, the tube diameter, d, was 18 mm, and the tube pitch, p, was 22.5 mm (p/d = 1.25). The local heat transfer had the highest values around θ = ± 90° where the liquid velocities were high in single-phase, bubbly and intermittent flows for both in-line and staggered arrays. A significant improvement in the heat transfer caused by the bubble motion was present for the in-line array as compared to the staggered array. Owing to the fluctuation of the liquid velocity, the heat transfer coefficient fluctuated significantly under intermittent flow conditions. In the bubbly flow at p/d = 1.25, the average heat transfer coefficient around a tube for the in-line array was higher than that for the staggered array. In contrast, the heat transfer coefficient of the staggered array was high under intermittent flow at a lower gas flow rate. This tendency is different from the results at p/d = 1.5. With a decrease in the relative size between the bubble diameter and the tube gap, there was a high improvement in the heat transfer coefficient due to the liquid agitation in the bubbly flow.