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This Article Full Text Full Text (PDF) All Versions of this Article: 297/1/C102    most recent 00354.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Fioretti, B. Articles by Franciolini, F. PubMed PubMed Citation Articles by Fioretti, B. Articles by Franciolini, F.

MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Histamine hyperpolarizes human glioblastoma cells by activating the intermediate-conductance Ca²⁺-activated K⁺ channel

¹Dipartimento di Biologia Cellulare e Ambientale, Universita' di Perugia, Perugia, Italy; and ²Dipartimento di Fisiologia e Farmacologia, Università di Roma "Sapienza", Roma, Italy

Submitted 8 July 2008 ; accepted in final form 17 April 2009

The effects of histamine on the membrane potential and currents of human glioblastoma (GL-15) cells were investigated. In perforated whole cell configuration, short (3 s) applications of histamine (100 µM) hyperpolarized the membrane by activating a K⁺-selective current. The response involved the activation of the pyrilamine-sensitive H₁ receptor and Ca²⁺ release from thapsigargin-sensitive intracellular stores. The histamine-activated current was insensitive to tetraethylammonium (3 mM), iberiotoxin (100 nM), and d-tubocurarine (100 µM) but was markedly inhibited by charybdotoxin (100 nM), clotrimazole (1 µM), and 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34, 1 µM), a pharmacological profile congruent with the intermediate conductance Ca²⁺-activated K⁺ (IK_Ca) channel. Cell-attached recordings confirmed that histamine activated a K⁺ channel with properties congruent with the IK_Ca channel (voltage independence, 22 pS unitary conductance and slight inward rectification in symmetrical 140 mM K⁺). More prolonged histamine applications (2–3 min) often evoked a sustained IK_Ca channel activity, which depended on a La²⁺ (10 µM)-sensitive Ca²⁺ influx. Intracellular Ca²⁺ measurements revealed that the sustained IK_Ca channel activity enhanced the histamine-induced Ca²⁺ signal, most likely by a hyperpolarization-induced increase in the driving force for Ca²⁺ influx. In virtually all cells examined we also observed the expression of the large conductance Ca²⁺-activated K⁺ (BK_Ca) channel, with a unitary conductance of ca. 230 pS in symmetrical 140 mM K⁺, and a Ca²⁺ dissociation constant [K_D(Ca)] of ca. 3 µM, at –40 mV. Notably in no instance was the BK_Ca channel activated by histamine under physiological conditions. The most parsimonious explanation based on the different K_D(Ca) for the two K_Ca channels is provided.

histamine; intermediate conductance Ca²⁺-activated K⁺ channels; large conductance Ca²⁺-activated K⁺ channels; human glioblastoma GL-15 cells