No abstract

Xenopus oocytes indicates that calcium-activated chloride currents are evoked by PACAP and vasoactive intinal polypeptide, sggesting that PACAPR-3 can also be coupled to phospholipase C. RNA blot analysis studies reveal that PACAPR-3 mRNA is expressed at high levels in MIN6, at moderate levels in pancreatic islets and other insulin-secreting cell lines, HIT-T15 and RINm5F, as well as in the lung, brain, stomach, and colon, and at low levels in the heart. Furthermore, insulin secretion from MIN6 cells is scantiy stimulated by PACAP-38. These results suggest that the diverse biological effects of PACAP are mediated by a family of structurally related proteins and that PACAPR-3 participates in the regulation of insulin secretion.

The self-association of acetic acid in organic solvents at 25 °C has been investigated by infrared spectroscopy. The organic solvents used are n-hexane, carbon tetrachloride, toluene, benzene, chlorobenzene, chloroform, 1,2-dichloroethane, and dichloromethane. The spectra of the carbonyl region were fitted with four Lorentzian curves, two for acetic acid monomer and cyclic dimer and the other two for the linear dimer. The formation constants of the cyclic and linear species were determined over concentration range from 8.4 X 10"3 to 1.3 x 10"1 mol dm'3. The solvent effect on the dimerization is considered in relation to the solvent effect on the partition of the acid monomer.

The structure of graphite fluoride, (C2F)n has been investigated by X‐ray analyses, solid state 19F‐n.m.r., and electron microscopy for well characterized and crystallized samples obtained from natural graphite or HOPG (highly oriented pyrolytic graphite). On the basis of the present results and structural properties derived from previous works, (C2F)n has a layered structure of stage‐2 which belongs hexagonal to the system with C3h symmetry. Detailed discussions on the symmetry both for (CF)n and (C2F)n have led to possible stacking sequences each unit cell of graphite fluoride should require. The ideal structure of (C2F)n is a hexagonal crystal lattice with a = b = 2.5 Å; c = 16.2 Å, and a plausible stacking sequence of AB/B′A′/ with Ic (identity period) = 8.09 Å. The layered structure of (CF)n is of stage‐1 with A/A′/ stacking sequence.

Dihydropyridine-sensitive voltage-dependent calcium channels (VDCC) play a crucial role in insulin secretion. We recently have cloned a human alpha 1-subunit of the VDCC expressed in pancreatic beta-cells, designated CACN4. In this study we have isolated complementary DNAs encoding two forms of rat CACN4 (rCACN4A and rCACN4B) from a rat insulinoma RINm5F complementary DNA library. Rat CACN4A is a protein of 2203 amino acids and is the rat homolog of human CACN4, whereas rCACN4B lacks 535 amino acids in the carboxyl-terminal region, probably due to alternative splicing. We have found two additional variations, one in the intracellular loop between repeats I and II and the other in the extracellular region between the third and fourth segments of repeat IV. Reverse transcriptase-polymerase chain reaction analysis of rat pancreatic islet messenger RNA reveals that these variants are present in pancreatic islets. In addition, whole-cell voltage-clamp recordings of Chinese hamster ovary cells stably expressing the alpha 1-subunit (rCACN4A or rCACN4B) with or without the calcium channel beta 2-subunit show that coexpression of rCACN4A with the beta 2-subunit or rCACN4B with the beta 2-subunit elicits L-type VDCC currents, whereas expression of the alpha 1-subunit alone does not, indicating that CACN4 can associate functionally with the beta 2-subunit and that the beta-subunit is essential for functional expression of CACN4. These results suggest that there are various subtypes of CACN4 expressed in pancreatic beta-cells, and that both rCACN4A and rCACN4B can function as VDCC. Furthermore, the present study suggests that the expression of the beta-subunit as well as the alpha 1-subunit may participate in the regulation of insulin secretion.