Neuroligand-mediated calcium signaling in cultured human schwannoma cells.

Intracellular Ca2+ release regulates proliferation of nonexcitable cells, however, it is not known whether and which neuroligands modulate the free intracellular Ca2+ concentration in human schwannoma cells. Confocal laser scanning microscopy was used for the study of neuroligand-induced Ca2+ signaling in cultured human schwannoma cells loaded with the Ca2+-sensitive fluorescent dyes Calcium Green-1 and Fura Red. Intracellular Ca2+ transients were observed during bath application of ATP (90% of cells tested), endothelin (60%), and norepinephrine (20%); histamine, serotonin, glutamate, and bradykinin did not have this effect. Two types of P2Y nucleotide receptor subtypes involved in ATP-induced Ca2+ transients could be separated by application of different P2Y receptor agonists and cross desensitization experiments: P2Y1 (rank order of potency: 2-MeSADP > 2-MeSATP > ADP > ATP) and P2Y2 (sensitive to UTP and ATP). Endothelin-induced Ca2+ signaling was also seen during application of [Ala(1,3,11,15)]ET-1; this suggests the presence of an ET(B) receptor subtype. The results indicate that the presence of receptors linked to neuroligand-triggered Ca2+ signaling does not seem to be abnormal in a human Schwann cell tumor, i.e. schwannoma cells retain this characteristic of peripheral glia.

Confocal calcium imaging reveals an ionotropic P2 nucleotide receptor in the paranodal membrane of rat Schwann cells.

1. The paranodal Schwann cell region is of major importance for the function of a myelinated axon. In the present study we searched for a possible ionotropic effect of extracellular ATP in this Schwann cell compartment. 2. Whole-cell patch-clamp recordings from cultured rat Schwann cells revealed that ATP and 2'-3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP) induced a non-specific cation current. The effect of ATP was much enhanced in a Ca2+- and Mg2+-free solution. ADP, UTP and alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-meATP) had no effect. 3. Confocal Ca2+ imaging of myelinating Schwann cells in isolated rat spinal roots showed a BzATP-induced rise in the free intracellular Ca2+ concentration in the paranodal Schwann cell cytoplasm whereas alpha,beta-meATP and 2-(methylthio)-adenosine 5'-triphosphate were without effect. In contrast to the known metabotropic effect of UTP on these Schwann cell regions, the BzATP-induced Ca2+ signal was not transient, was unaffected by depletion of intracellular Ca2+ stores and dependent on the presence of extracellular Ca2+. 4. These results suggest that an ionotropic ATP receptor with electrophysiological and pharmacological characteristics of the P2X7 subtype of nucleotide receptors is functionally active in myelinating Schwann cells of peripheral nerves. Such a receptor might contribute to Schwann cell reactions in nerve injury or neuropathy.