MEMBRANE POTASSIUM CHANNELS AND HUMAN BLADDER-TUMOR CELLS - I - ELECTRICAL-PROPERTIES

These experiments were conducted to determine the membrane K+ currents and channels in human urinary bladder (HTB-9) carcinoma cells in vitr o. K+ currents and channel activity were assessed by the whole-cell vo ltage clamp and by either inside-out or outside-out patch clamp record ings. Cell depolarization re suited in activation of a Ca2+-dependent outward KC current, 0.57 +/- 0.13 nS/pF at -70 mV holding potential an d 3.10 +/- 0.15 nS/pF at 30 mV holding potential. Corresponding patch clamp measurements demonstrated a Ca2+-activated, voltage-dependent K channel (I,,) of 214 +/- 3.0 pS. Scorpion venom peptides, charybdotox in (ChTx) and iberiotoxin (IbTx), inhibited both the activated current and the K-Ca activity. In addition, on-cell patch recordings demonstr ated an inwardly rectifying KC channel, 21 +/- 1 pS at positive transm embrane potential (V-m) and 145 +/- 13 pS at negative V-m. Glibenclami de (50 mu M), Ba2+ (1 mM) and quinine (100 mu M) each inhibited the co rresponding nonactivated, basal whole-cell current. Moreover, glibencl amide inhibited K+ channels in inside/out patches in a dose-dependent manner, and the IC50 = 46 mu M. The identity of this K+ channel with a n ATP-sensitive K+ channel (K-ATP) was confirmed by its inhibition wit h ATP (2 mM) and by its activation with diazoxide (100 mu M). We concl ude that plasma membranes of HTB-9 cells contain the K-Ca and a lower conductance KC channel with properties consistent with a sulfonylurea receptor-linked K-ATP.