The conductive properties of exponentially dividing LNCaP prostate cancer cells

Abstract

The intermediate conductance Ca2+‐activated K+ channel (hIK1) is thought to be involved in the cell division of cancer cells. However, direct measurements of the expression and properties of hIK1 during the cell cycle have not been made. Therefore, as an initial step in defining the role of hIK1 in the cell cycle we have measured the conductive properties of exponentially growing LNCaP cells using the whole cell patch clamp technique. Flow cytometry analysis indicated that 24 h after plating 84% of the cells were in the G1 phase, and 7% and 8% of the cells were in the S and G2/M phases, respectively (n = 4). In these cells three distinct conductances were identified in different cells. The majority of the cells (18 out of 29 cells) exhibited an outwardly rectified K+ current. In the presence of 500 μM free Ca2+, this current was inhibited by 10 mM tetraethylammonium (TEA) (n = 8, P < 0.0001) but not the hIK1 inhibitor clotrimazole (10 μM, n = 3, P = 0.11). Furthermore, 1‐EBIO (100 μM), an activator of hIK1, did not stimulate an increase in current in these cells (n = 3, P = 0.27). In a second group of cells (5 of 29) an outwardly rectified current was also seen, but this was relatively insensitive to TEA. In the remaining 5 cells the dominant current was inwardly rectified. 1‐EBIO increased this current from ‐2.7 ± 1.3 to ‐10.8 ± 6.7 pA pF−1 at ERev‐60 mV (n = 3, P = 0.2), but the increase was not significant suggesting the lack of hIK1 activity. Therefore, if hIK1 is involved in proliferation of LNCaP cells, there must be a dramatic change in the expression level or biophysical properties of the channel as the cells proceed through the cell cycle. This work was funded by Grants from the HS & JC Anderson Trust and Lotteries Health.