HISTAMINE H-1 RECEPTORS IN UC-11MG ASTROCYTES AND THEIR REGULATION OF CYTOPLASMIC CA-2+

Experiments were carried out on UC-11MG human astrocytoma cells, a continuous cell line that expresses a broad range of the biochemical and electrophysiological properties found in well-differentiated astrocytes. Because of a number of recent reports that astrocytes may express receptors for a variety of neuro-active substances, we measured the effects of 12 different neurotransmitters on intracellular free Ca2+(Ca(i)2+) in UC-11MG cells. Of these neurotransmitters only histamine was found to have a significant effect. Further characterization of the nature of the histamine response showed that UC-11MG cells express mepyramine-sensitive H-1 receptors the activation of which causes both mobilization of Ca2+ from intracellular stores and entry of Ca2+ from the extracellular solution. No evidence was found for the presence of H-2 receptors. The Ca(i)2+ response was maximal at 300 muM histamine and was attenuated by increasing cell density. We suggest that this neurotransmitter may play a role in astrocytic function in the human CNS.