A 23-pS Ca2+-activated K+channel in MCF-7 human breast carcinoma cells: an apparent correlation of channel incidence with the rate of cell proliferation

✍ Scribed by E. A. Wegman; J. A. Young; D. I. Cook

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 978 KB
• Volume: 417
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00372952

✦ Synopsis

In studies on the apical membranes of cultured MCF-7 human breast carcinoma cells, we found two conspicuous K § channel types with conductances of 23 and 70 pS, respectively. Of these, the 23-pS K § channel was most conspicuous. In cell-attached patches with KC1 in the pipette, it had a linear current/voltage (I/V) relation and was activated by depolarisation and in excised insideout patches it was highly selective for K + over Na § (permeability ratio of Na § to K § PNa/PK = 0.02). Rubidium (Rb +) had a similar permeability to K § although it was only conducted at 20% of the rate of K § and cesium (Cs § had a permeability less than 30% that of K § and was not conducted at all. Both Cs § and Rb § acted as partial blockers when applied internally but the channel was not blocked by external tetraethylammonium (TEA, 10 mmol/1), quinidine (200 ~tmol/1) or apamin (50 nmol/1). It was activated by Ca 2 + in the range 10 .7-10 -6 mol/1. In cell-attached patches at a pipette potential of 0 mV, the open-time histogram was described by a single exponential (time constant 1.6 ms) and the closed-time histogram by two exponentials (time constants 0.5 and 1.5 ms). The incidence of the 23-pS but not the 70-pS channel depended on the rate of cell proliferation. Thus, in studies on cell-attached patches from cells in the exponential growth phase, the 23-pS channel was observed in 78% of patches. However, when the proliferation rate was decreased, whether as a result of allowing the monolayer to reach confluence, or of cell treatment with an anti-oestrogen (tamoxifen, 10 gmol/1), or a phorbol ester [phorbol 12-myristate 13-acetate (TPA), 2.6 nmol/1], the channel incidence was reduced to 42%, 60% and 42%, respectively. The activity of the 23-pS channel is not obligatory for cell division, however, since the rate of cell proliferation remained the same in MCF-7 cultures in which the channel was not expressed.