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A study was conducted on pepsinogen secretion and its relation to Ca2+ changes over short time periods. The findings indicate that initial exocytosis is related to the mobilization of Ca2+ from intracellular pools and that Ca2+ influx from the extracellular medium is responsible for continuing exocytosis in from pepsinogen-secreting cells. Moreover, there is a relation between continued exocytosis at lower levels and Ca2+ oscillation.

Photosynthetic water oxidation takes place through the light-driven cycle of five intermediates (S0–S4) of the water oxidizing complex (WOC), which consists of the Mn4CaO5 cluster and surrounding amino acid residues in photosystem II. Clarifying the protonation structures of the Mn4CaO5 cluster and its water ligands (W1–W4) is essential for understanding the molecular mechanism of water oxidation. Here, we performed normal mode analysis of WOC in the S0 and S1 states using quantum mechanics/molecular mechanics calculations and simulated an S1-minus-S0 infrared difference spectrum focusing on the symmetric COO− stretching (νsCOO−) region. The calculated spectrum by an S0 model, in which O4 of the Mn4CaO5 cluster is protonated and W2 is H2O, and a corresponding S1 state with deprotonated O4 best reproduced the νsCOO− features of the experimental spectrum, whereas models with protonated O5 showed poor agreement. In addition, comparison of the calculated coordination distances of the water ligands with the experimental data by X-ray diffraction analysis indicates that W2 is most probably not OH− but H2O both in the S0 and S1 states. The present calculations thus strongly suggest that the S0 state has a protonation structure of O4–H and W2 = H2O. The O4–H structure in the S0 state supports the view that this proton is released through the O4–water chain immediately after electron transfer during the S0 → S1 transition. [ABSTRACT FROM AUTHOR]

Primary cultures of adult mouse hepatocytes are shown here to reexpress differentiated hepatocyte features following treatment with 2% DMSO and [10.sup.-7] M glucagon. To examine the roles of gap junctional communication during hepatocyte growth and differentiation, we have compared treated and untreated hepatocytes from connexin (Cx)32-deficient [Cx32 knockout (KO)] and wild-type mice. In untreated cultures, DNA replication of Cx32 KO hepatocytes was markedly higher than of wild types. Although Cx26 mRNA levels remained high at all time points in wild-type and Cx32 KO hepatocytes, Cx32 mRNA and protein in wild-type hepatocytes underwent a marked decline, which recovered in 10-day treated cultures. Increased levels of Cx26 protein and junctional conductance were observed in Cx32 KO hepatocytes at 96 h in culture, a time when cell growth rate was high. Treatment with DMSO/glucagon highly reinduced Cx26 expression in Cx32 KO hepatocytes, and such treatment reinduced expression of both Cx32 and Cx26 expression in wild types. Dye transfer was not observed following Lucifer yellow injection into DMSO/glucagon-treated Cx32 KO hepatocytes, whereas the spread was extensive in wild types. Nevertheless, high junctional conductance values were observed in treated cells from both genotypes. These studies provide a method by which the differentiated phenotype can be obtained in cultured mouse hepatocytes and provide in vitro evidence that expression of gap junctions formed of Cx32 are involved in the regulation of growth of mouse hepatocytes. connexin32; connexin26; knockout mice