Myogenic differentiation in vitro has been usually viewed as being negatively controlled by serum mitogens. A depletion of critical serum components from medium has been considered to be essential for permanent withdrawal from the cell cycle and terminal differentiation of myoblasts. Removal of serum mitogens induces the expression of insulin-like growth factors (IGFs), whereas it inhibits that of basic fibroblast growth factor (bFGF) and transforming growth factor (TGF)-beta in myoblasts. These responses of growth factors to medium conditioning seem to be well matched to their functions in proliferation/differentiation. In the present study, we showed that C(2)C(12) myoblasts differentiated actively, even in mitogen-rich medium, and that this medium offered an advantage over mitogen-poor medium in terms of increasing differentiation. Our attention focused on endogenous growth factors, as described above, especially IGFs in mitogen-rich medium. During differentiation, IGF-I and IGF-II mRNA levels increased, but bFGF and TGF-beta(1) mRNAs decreased. Differentiation was commensurable with IGF mRNA levels and suppressed by antisense oligodeoxynucleotides and neutralizing monoclonal antibodies against IGFs. These results suggest that an autocrine/paracrine loop of IGFs, bFGF, and TGF-beta(1) is active in proliferating and differentiating C(2)C(12) cells without a depletion of serum and that endogenous IGFs actively override the negative control of differentiation by serum mitogens.

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The title compound, C28H20N4O4, is an organic pigment. The molecule has Ci symmetry. Accordingly, the pyridylethyl groups are arranged in a trans fashion across the naphthaleneimide skeleton. The interplanar distance between the two aromatic systems is 12.846 (2) Å and this clearly indicates a lack of π–πinteractions, as also shown by similar spectra in solution and in the solid state.

We have been involved in the research and development on H 2 gas sensors utilizing a high proton affinity of the pyridyl rings integrated in organic pigments such as diketopyrrolopyrroles, peryleneimides, and copperphthalocyanes. Our sensors exhibit a remarkable increase in electrical conductivity by three orders of magnitude even under 0.01% H 2. However, an anomalous phenomenon has been observed in the title compounds ͑pyridylimidazoperylene and pyridylimidazonaphthalene͒ that shows an additional increase in conductivity ͑i.e., reverse of the sensor current͒ as soon as H 2 shuts off. The unusual effect has been investigated in the present investigation on the basis of the crystal structure, molecular orbital calculations, and UV-visible/IR spectra with special attention to the sign of the charge carriers before and after exposure to H 2. As a result, the pyridylimidazole ring is found to be responsible for the unusual effect that involves two protonation sites. In addition, the charge carriers have been determined to be solely electrons in the build up of the sensor current; whereas both electrons and protons are involved in the decay process. The contribution of the proton conduction in the decay process prevails over the electron current, ending up with the reverse in sensor current.