BKCa channels activating at resting potential without calcium in LNCaP prostate cancer cells

Large-conductance Ca2+-dependent K+ (BKCa) channels are activated by intracellular Ca2+ and membrane depolarization in an allosteric manner. We investigated the pharmacological and biophysical characteristics of a BKCa-type K+ channel in androgen-dependent LNCaP (lymph node carcinoma of the prostate) cells with novel functional properties, here termed BKL. K+ selectivity, high conductance, activation by Mg2+ or NS1619, and inhibition by paxilline and penitrem A largely resembled the properties of recombinant BKCa channels. However, unlike conventional BKCa channels, BKL channels activated in the absence of free cytosolic Ca2+ at physiological membrane potentials; the half-maximal activation voltage was shifted by about -100 mV compared with BKCa channels. Half-maximal Ca2+-dependent activation was observed at 0.4 mu M for BKL (at -20 mV) and at 4.1 mu M for BKCa channels (at +50 mV). Heterologous expression of hSlo1 in LNCaP cells increased the BKL conductance. Expression of hSlo-beta 1 in LNCaP cells shifted voltage-dependent activation to values between that of BKL and BKCa channels and reduced the slope of the P-open (open probability)-voltage curve. We propose that LNCaP cells harbor a so far unknown type of BKCa subunit, which is responsible for the BKL phenotype in a dominant manner. BKL-like channels are also expressed in the human breast cancer cell line T47D. In addition, functional expression of BKL in LNCaP cells is regulated by serum-derived factors, however not by androgens.