Okadaic acid‐sensitive activation of Maxi Cl⁻ channels by triphenylethylene antioestrogens in C1300 mouse neuroblastoma cells

Abstract

The regulation of Maxi Cl− channels by 17β‐oestradiol and non‐steroidal triphenylethylene antioestrogens represents a rapid, non‐classical effect of these compounds. In the present study we have investigated the signalling pathways used for the regulation of Maxi Cl− channel activity by oestrogens and antioestrogens in C1300 neuroblastoma cells. Whole‐cell Maxi Cl− currents were readily and reversibly activated by tamoxifen, toremifene and the membrane‐impermeant ethyl‐bromide tamoxifen, only when applied to the extracellular medium. Pre‐treatment of C1300 cells with oestrogen or cAMP prevented the antioestrogen‐induced activation of Maxi Cl− channels. The inhibitory effect of 17β‐oestradiol and cAMP was abolished by the kinase inhibitor staurosporine. Current activation was unaffected by the removal of intracellular Ca2+ and Mg2+, but was completely abolished in the presence of okadaic acid. These results are consistent with the participation of an okadaic acid‐sensitive serine/threonine protein phosphatase in the activation of Maxi Cl− channels. However, neither oestrogen or antioestrogen treatment modified the total activity of the two major serine/threonine phosphatases, PP1 and PP2A, in C1300 cells. Although the role of these Maxi Cl− channels remains unknown, our findings suggest strongly that their modulation by oestrogens and antioestrogens is linked to intracellular signalling pathways.

The maxi-anion channel: a classical channel playing novel roles through an unidentified molecular entity

“…The effect could be blocked by 17b-estradiol but not by progesterone. A similar effect of these antiestrogens on C1300 neuroblastoma cells was blocked by okadaic acid, suggesting a role of Ser/ Thr phosphorylation in this process [42]. Henriquez and …”

“…In the heart, maxianion channels were described in neonatal cardiac myocytes in primary culture [2,12,34,35] and freshly isolated adult ventricular cardiomyocytes [12]. In the nervous system, the maxi-anion channel activity was detected in embryonic Xenopus spinal neurons [36], demyelinated Xenopus axons [37], in neuroblastoma cell lines [3,[38][39][40][41][42][43][44] and in a hippocampal cell line [45,46]. In glia, maxi-anion channels were found in cultured Schwann cells from 1 to and in inside-out patches (filled circles).…”

“…-ATPase [115]. Regulation by estrogens and antiestrogens links the maxi-anion channel to the intracellular signaling pathways of the cells expressing estrogen receptors [42,89]. A possible role in signal transduction in B cell activation [99,100] and in receptor-mediated initial cell depolarization in colonic smooth muscle cells [29] has also been proposed.…”

A Novel Human Cl- Channel Family Related to Drosophila flightless Locus

“…However, there is argument against a direct ligand-type Ca 2ϩ dependence in the activation of maxiCl Ϫ channels. Some maxi-Cl Ϫ channels are activated by polymyxin B, an inhibitor of protein kinase C (6), G-protein (24), or okadaic acid (30). Although we used various reagents to investigate the regulation, none of them activated the hTTYH3 channel.…”

Plasma Membrane Voltage-dependent Anion Channel Mediates Antiestrogen-activated Maxi Cl– Currents in C1300 Neuroblastoma Cells

“…Cell Culture and Chemicals-C1300 mouse neuroblastoma cells, obtained from the Imperial Cancer Research Fund Laboratories, Clare Hall, Herts, UK, were cultured as described previously (8). For experimental procedures, cells were plated onto 35-mm culture dishes (NUNC) or 13-mm glass coverslips treated with poly-D-lysine (10 g/ml for 1 h).…”