Search

To obtain compounds that promote glucose uptake in muscle cells, the novel cell lines A31-IS derived from Balb/c 3T3 A31 and C2C12-IS from mouse myoblast C2C12 were established. In both cell lines, glucose consumption was induced by insulin and suppressed by the addition of Akt-activating kinase inhibitor. The A31-IS cells highly express the insulin receptor β chains, Glut4, and uncoupling protein-3, as compared to the parent Balb /c 3T3 A31 cells, and C2C12-IS cells highly express the insulin receptor β chain as compared to its parent cell line. Using A31-IS cells, we screened our library compounds and obtained three compounds, DF-4394, DF-4451, and DG-5451. These compounds dose-dependently promoted glucose consumption in A31-IS cells and facilitated [3H]-2-deoxyglucose uptake in differentiated C2C12-IS cells. The compounds that we obtained from the library screening will be good candidates for improving insulin resistance in muscle cells. Keywords:: skeletal muscle cell, insulin, glucose uptake

Corticotropin-releasing factor (CRF) increased intracellular Ca 2+ concentration in single astrocytes. The effect in increasing intracellular Ca 2+ was not observed in Ca 2+ -free solution. Furthermore, CRF at concentrations more than 10 nM stimulated 45 Ca 2+ uptake in cultured rat astrocytes. The action was blocked by α-helical CRF(9-41) in a competitive manner, but not by nifedipine and 3,4-dichlorobenzamil. On the other hand, CRF did not stimulate cAMP formation, cGMP formation and phosphoinositide hydrolysis in astrocytes. These results indicate that CRF increases Ca 2+ influx via an activation of CRF receptors in a cAMP-independent mechanism in cultured astrocytes.

Effect of endothelin-3 (ET-3) on dibutyryl cAMP (DBcAMP)-induced stellation of rat cerebral cultured astrocytes was examined. Treatment with 1 mM DBcAMP, 10 μM forskolin, 100 μM isoproterenol and 500 nM phorbol 12-myristate 13-acetate changed protoplasmic cultured astrocytes into process-bearing ones. ET-3 (1 nM) completely prevented the astrocytic stellation induced by these agents. The effect of ET-3 showed a dose-dependence, where IC 50 value and maximal effective dose were 49 pM and about 0.1 mM, respectively. ET-1 and sarafotoxin (SRTX) S6b prevented the DBcAMP-induced astrocytic stellation with potencies similar to that of ET-3. ET-3 (1 nM) did not affect the cAMP accumulation after DBcAMP treatment in cultured astrocytes. Stellate astrocytes were reversed to the protoplasmic type cells by addition of 1 mN ET-3 in the presence of DBcAMP. ET-1 and SRTX similarly reversed the astrocytic stellation. ET-3 reversed the astrocytic stellation in the absence of extracellular Ca 2+ . Pre-loading of BAPTA-AM, a permeable Ca 2+ chelator, on stellate astrocytes had no effect on the reversal by ET-3. ET-3 did not increase intracellular free Ca 2+ concentration ([Ca 2+ ] i ) of most astrocytes tested at 0.1 nM. A high concentration (100 nM) of ET-3 increased astrocytic [Ca 2+ ] i which was negated by Ca 2+ -free and BAPTA-AM loading. These results suggest that ETs modulate morphological changes in astrocytes through cAMP- and Ca 2+ -independent mechanisms.