Functional cardiac Na+ channels are expressed in human melanoma cells

Resting membrane potential (RMP) and intracellular Ca²⁺ concentration [(Ca²⁺)_i] are involved in tumorigenesis and metastasis. The present study investigated whether functional cardiac Na⁺ channels are expressed in human melanoma cells (WM 266-4) and its nonmalignant human melanocytes (HMC), as well as whether they participate in RMP maintenance and Ca²⁺ homeostasis. Confocal microscopy and western blot analysis were used to detect Na⁺ channels. The patch-clamp technique was employed to record Na⁺ currents and action potentials. Cytoplasmic Ca²⁺ was measured by loading Fluo-4. Cardiac (Na_v1.5) Na⁺ channels were expressed in HMCs and WM 266-4 cells. Tetrodotoxin (TTX) dose-dependently blocked Na⁺ currents in WM 266-4 while HMCs had no Na⁺ currents. Ultraviolet light induced similar action potentials in HMCs and WM 266-4 cells, which were abolished by transient receptor potential A1 channel-specific blocker, HC-030031. Compared with HMCs, RMP was substantially depolarized in WM 266-4. TTX hyperpolarized RMP in WM 266-4 cells at a concentration of 30 µM, which facilitated Ca²⁺ influx. Compared with HMCs, (Ca²⁺)_i was significantly higher in WM 266-4 cells and was elevated by 30 µM TTX. Collectively, Cardiac Na⁺ channels depolarize RMP and inhibit Ca²⁺ uptake in melanoma cells possibly contributing to tumorigenesis and metastasis. Na⁺ channel agonists may be developed to treat melanoma such as WM 266-4.

Abstract 234A: Aberrant sodium current contributes to constitutive mTOR activity in malignant melanoma cells

Transformation from disciplined melanocytes to untamed melanoma cells remains an enigma. Our previous studies have demonstrated that melanoma cells are more resistant to oxidative stress and melanoma cells exhibit constitutive mTOR activity. Surprisingly, further studies have failed to present the expression and activity of EGFR using conventional anti-EGFR antibodies. We hypothesized that constitutive mTOR activity in melanoma cells may be due to mutated EGFR variants and membrane channel activities. Using patch clamping technique, we have shown that melanoma cells (WM 266-4) but not human skin melanocytes exhibit Na+ current which is blocked by TTX. Interestingly, mTOR inhibitor, rapamycin, blocks Na+ current. Western blot and confocal microscopy data further revealed that Na+/Ca2+ exchanger blocker KB-R7943 (KBR), and L-type Ca2+ channel blocker Nifedipine (NIF) inhibits mTOR activity in melanoma cells in a dose dependent manner. To further characterize Na+ channels, we used commercially available channel antibodies. Western blot analysis data showed that melanoma cells but not human melanocytes express Na+ v1.5 and Na+ v1.6 and NCX3. Functional studies also indicated that KBR and NIF inhibit melanoma cell proliferation and migration. Taken all together, our data suggest that aberrant Na+ current contributes to constitutive mTOR activity in melanoma cells and channel blockers may be potential for the treatment of melanoma.

Citation Format: Benjamin Gallant, Nicole Lizza, Ryan Garrity, Audrey Madigan, Zachary Jost, Alfredo Gonzalez, Jeanine Justiniano, An Xie, Yinsheng Wan. Aberrant sodium current contributes to constitutive mTOR activity in malignant melanoma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 234A.

Recovery characteristics following induction of anaesthesia with a combination of thiopentone and propofol

The purpose of this study was to determine the rate and quality of recovery when general anaesthesia was induced with a mixture of thiopentone and propofol, compared with thiopentone or propofol alone. Sixty ASA class I and II women scheduled for out-patient laparoscopic surgery underwent induction of anaesthesia with either (i) thiopentone, (ii) propofol, or (iii) a mixture of the two, in a randomized, double-blind fashion. Anaesthesia was then maintained using nitrous oxide, isoflurane and fentanyl. A psychometric test was administered before and after surgery, and the time taken to reach a series of recovery milestones was noted. Patients were discharged as soon as they were ambulant and had satisfactory control of pain and nausea with oral agents. They were telephoned at 24-48 hr later, and asked to rate their experience of a list of side effects on an ordinal scale. Patient groups were demographically comparable and underwent surgery of the same duration. Those receiving thiopentone were discharged after a mean time of 3 hr 25 +/- 58 min (SD). The corresponding figures for propofol and the thiopentone/propofol mixture were 2 hr 40 min (+/- 49) and 2 hr 48 min (+/- 68) respectively. The recovery time between thiopentone and the other two regimes was different (P < 0.05). All three groups experienced equally frequent and severe nausea, headache, tiredness and other side effects during the next 24 hr. It is concluded that induction with a mixture of thiopentone and propofol leads to a similar rate and quality of recovery to that of propofol above.(ABSTRACT TRUNCATED AT 250 WORDS)