Electrophysiological characterization of voltage-gated Na+ current expressed in the highly metastatic Mat-LyLu cell line of rat prostate cancer.
Voltage-gated Na+ channels, classically associated with impulse conduction in excitable tissues, are also found in a variety of epithelial cell types where their possible functions are not known so well. We have previously reported expression of a voltage-gated Na+ channel specifically in the highly metastatic Mat-LyLu rat prostate cancer cell line; blockage of the current with tetrodotoxin (TTX) significantly reduced the invasiveness of the cells in vitro, suggesting that the channel may have a functional role in metastasis. The aim of the present study was to characterize this current using the whole-cell patch clamp recording technique, and compare it to Na+ currents found in various other tissues. The inward current of the Mat-LyLu cells was abolished completely, but reversibly, in Na+-free solution, confirming that Na+ was indeed the permeant ion. Activation occurred at -40 mV and currents reached a maximal amplitude at around 6 mV. Boltzmann fits to current activation and steady-state inactivation revealed that the currents were half activated at about -15 mV and half inactivated at -80 mV. Both current inactivation and recovery from inactivation followed a double-exponential time course with fast and slow components. The Na+ currents were highly sensitive to block by TTX (IC50 approximately 18 nM), whilst 1 microM mu-conotoxin GIIIA mostly had no effect. 100 microM Cd2+ also had no effect on the current, whilst 2.5 mM Cd2+, Mn2+, and Co2+ each caused a depolarizing shift in activation and a reduction in peak conductance of around 20%. In conclusion, the Na+ channel expressed in the highly metastatic Mat-LyLu cell line appeared to have electrophysiological and pharmacological properties of TTX-sensitive channels. Further work is needed, however, to elucidate the exact nature of the channel protein and the mechanism(s) of its involvement in cellular invasiveness.
Grimes
J A
JA
Department of Biology, Imperial College of Science, Technology and Medicine, London, United Kingdom.
Djamgoz
M B
MB
D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology; D020916:Conotoxins; D004558:Electric Stimulation; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008297:Male; D018408:Patch-Clamp Techniques; D010456:Peptides, Cyclic / Q000494:pharmacology; D011471:Prostatic Neoplasms; D051381:Rats; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000737:chemistry / Q000502:physiology
D002413:Cations, Divalent; D020916:Conotoxins; D010456:Peptides, Cyclic; D015222:Sodium Channels; C046101:conotoxin GIII; D013779:Tetrodotoxin; D012964:Sodium