When a water droplet spreads on a vertically aligned nanorod surface, the nanorod array will deform into statistically percolated patterns. This nanocarpet effect has been investigated for Si nanorods. Three distinct morphologies were found: a center region due to the water droplet impact, a tilting region due to gravity, and a percolation region due to capillary invasion. The corresponding capillary forces have been estimated through finite element analysis. This effect presents a challenge for nanodevices involving liquid interactions.

The endogenous phospholipid mediator lysophosphatidic acid (LPA) caused growth cone collapse, neurite retraction, and cell flattening in differentiated PC12 cells. Neurite retraction was blocked by cytochalasin B and ADP‐ribosylation of the small‐molecular‐weight G protein Rho by the Clostridium botulinum C‐3 toxin. LPA induced a transient rise in the level of inositol 1,4,5‐trisphosphate, and retraction was blocked by inhibitors of phospholipase β. Repeated application of LPA elicited homologous desensitization of the Ca2+ mobilization response. The activation of the phosphoinositide (PIP)‐Ca2+ second messenger system played a permissive role in the morphoregulatory response. Blockers of protein kinase C—chelerythrine, a myristoylated pseudosubstrate peptide, staurosporine, and depletion of protein kinase C from the cells by long‐term phorbol ester treatment—all diminished neurite retraction by interfering with LPA‐induced Ca2+ mobilization, which was required for the withdrawal of neurites. A brief 15‐min treatment with 4β‐phorbol 12‐myristate 13‐acetate also blocked retraction and Ca2+ mobilization, by inactivating the LPA receptor. Inhibition of protein tyrosine phosphorylation by herbimycin diminished retraction. Although activation of the PIP‐Ca2+ second messenger system appears necessary for the Rho‐mediated rearrangements of the actin cytoskeleton, bradykinin, which activates similar signaling events, failed to cause retraction, indicating that a yet unidentified novel mechanism is also involved in the LPA‐induced morphoregulatory response.

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Previous studies showed that the normal microflora of the large intestine synthesizes biotin and that the colon is capable of absorbing intraluminally introduced free biotin. Nothing, however, is known about the mechanism of biotin absorption in the large intestine and its regulation. To address these issues, we used the human-derived, nontransformed colonic epithelial cell line NCM460. The initial rate of biotin uptake was found to be 1) temperature and energy dependent, 2) Na+ dependent (coupling ratio of 1:1), 3) saturable as a function of concentration [apparent Michaelis constant ( K m) of 19.7 μM], 4) inhibited by structural analogs with a free carboxyl group at the valeric acid moiety, and 5) competitively inhibited by the vitamin pantothenic acid (inhibition constant of 14.4 μM). Pretreatment with the protein kinase C (PKC) activators phorbol 12-myristate 13-acetate (PMA) and 1,2-dioctanoyl- sn-glycerol significantly inhibited biotin uptake. In contrast, pretreatment with the PKC inhibitors staurosporine and chelerythrine led to a slight, but significant, increase in biotin uptake. The effect of PMA was mediated via a marked decrease in maximal uptake velocity and a slight increase in apparent K m. Pretreatment of cells with modulators of the protein kinase A-mediated pathway, on the other hand, showed no significant effect on biotin uptake. These results demonstrate, for the first time, the functional existence of a Na+-dependent, specialized carrier-mediated system for biotin uptake in colonic epithelial cells. This system is shared with pantothenic acid and appears to be under the regulation of an intracellular PKC-mediated pathway.