These experiments were conducted to determine the membrane K+ currents and channels in human urinary bladder (HTB-9) carcinoma cells in vitro. K+ currents and channel activity were assessed by the whole-cell voltage clamp and by either inside-out or outside-out patch clamp recordings. Cell depolarization resulted in activation of a Ca2+-dependent outward K+ current, 0.57 ± 0.13 nS/pF at -70 mV holding potential and 3.10 ± 0.15 nS/pF at 30 mV holding potential. Corresponding patch clamp measurements demonstrated a Ca2+-activated, voltage-dependent K+ channel (K(Ca)) of 214 ± 3.0 pS. Scorpion venom peptides, charybdotoxin (ChTx) and iberiotoxin (IbTx), inhibited both the activated current and the K(Ca) activity. In addition, on-cell patch recordings demonstrated an inwardly rectifying K+ channel, 21 ± 1 pS at positive transmembrane potential (V(m)) and 145 ± 13 pS at negative V(m). Glibenclamide (50 μM), Ba2+ (1 mM) and quinine (100 μM) each inhibited the corresponding nonactivated, basal whole-cell current. Moreover, glibenclamide inhibited K+ channels in inside/out patches in a dose-dependent manner, and the IC50 = 46 μM. The identity of this K+ channel with an ATP-sensitive K+ channel (K(ATP)) was confirmed by its inhibition with ATP (2 mM) and by its activation with diazoxide (100 μM). We conclude that plasma membranes of HTB-9 cells contain the K(Ca) and a lower conductance K+ channel with properties consistent with a sulfonylurea receptor-linked K(ATP).
| Identifer | oai:union.ndltd.org:ETSU/oai:dc.etsu.edu:etsu-works-13262 |
| Date | 01 February 1998 |
| Creators | Monen, S. H., Schmidt, P. H., Wondergem, R. |
| Publisher | Digital Commons @ East Tennessee State University |
| Source Sets | East Tennessee State University |
| Detected Language | English |
| Type | text |
| Source | ETSU Faculty Works |
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