The characteristics of KCl-stimulated 45Ca uptake by neuroblastoma X glioma hybrid NG108-15 cells induced to differentiate with dibutyryl cAMP (Bt2cAMP) and of PC12h pheochromocytoma cells induced to differentiate with nerve growth factor (NGF) were studied. The extent and rate of KCl-stimulated 45Ca uptake by differentiated NG108-15 cells induced with Bt2cAMP were significantly higher than those of the undifferentiated cells. However, differentiation of PC12h cells induced with NGF did not enhance their extent or rate of KCl-stimulated 45Ca uptake. The effects of Ca agonist and antagonists indicated that the characteristics of KCl-stimulated 45Ca uptake by Bt2cAMP-treated NG108-15 cells and NGF-treated PC12h cells mainly reflected those of peripheral L-type voltage-sensitive calcium channels activated by high KCl. These results suggest that differentiated neural cells did not all show an enhanced capacity for KCl-stimulated 45Ca uptake, although the characteristic patterns of differentiation (extension of neurite-like processes, etc.) and that of effect by Ca agonist or antagonists on NG108-15 cells and PC12h cells were similar.

The characteristics of the specific bindings of [3H](+)PN200-110 (PN: L-type Ca channel antagonist) and [125I]omega-conotoxin G VI A (omega-CgTX: neuronal L- or N-type Ca channel antagonist) to crude membranes from undifferentiated neuroblastoma X glioma hybrid NG108-15 (NG108-15) cells and differentiated cells induced with dibutyryl cAMP (Bt2cAMP) were examined, because we have already observed that the magnitude and rate of KCl-stimulated 45Ca uptake by NG108-15 cells increased progressively during differentiation of the cells induced with Bt2-cAMP (unpublished results). The specific binding of [3H](+)PN to these crude membranes was saturable at various concentrations of 2.5-5.0 nM [3H](+)PN. Scatchard analysis showed that the specific binding of [3H](+)PN at equilibrium was significantly increased after differentiation of the NG108-15 cells with Bt2cAMP, but that the apparent Kd value for the specific binding of [3H](+)PN was not influenced by treatment with Bt2cAMP. The specific binding of [3H](+)PN to crude membranes from Bt2cAMP-treated NG108-15 cells was inhibited by a calcium agonist and antagonists, the order of their inhibitory potencies being (+)PN > nitrendipine > (-)PN > or = Bay K 8644 > > diltiazem = verapamil. Thus, PNs showed significant stereoselective inhibition of the specific binding of [3H](+)PN. On the other hand, [125I]omega-CgTX at concentrations of 0.075-0.6 nM showed scarcely any specific binding to these crude membranes, although at 0.6 nM it showed specific binding to crude membranes from rat brain in the same experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

ABSTRACT-We investigated the effects of various Ca channel agonists (Ca agonist) derived from 1,4-dihy dropyridine on KC1-stimulated 45Ca uptake by differentiated and undifferentiated neuroblastoma x glioma hybrid NG108-15 cells with and without dibutyryl cAMP. Ca agonists Bay K 8644, YC-170 and CGP 28392 enhanced KCl-stimulated 45Ca uptake in differentiated NG108-15 cells, but only slightly in undifferentiated NG108-15 cells. The rank order of the enhancing effects was roughly Bay K 8644 > YC-170 > CGP 28392. These results suggest that there is some difference between the mechanisms by which these Ca agonists affect KCl-stimulated 45Ca uptake in differentiated and undifferentiated NG108-15 cells, although the nature of that difference is not clear.