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.

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 KCl in the pipette, it had a linear current/voltage (I/V) relation and was activated by depolarisation and in excised inside-out 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/l), quinidine (200 mumol 1) or apamin (50 nmol/l). It was activated by Ca2+ in the range 10(-7)-10(-6) mol/l. In cell-attached patches at a pipette potential of O 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.(ABSTRACT TRUNCATED AT 250 WORDS)