Extracellular Electrophysiology in the Prostate Cancer Cell Model PC-3

Abstract

Although prostate cancer is one of the most common cancers in the male population, its basic biological function at a cellular level remains to be fully understood. This lack of in depth understanding of its physiology significantly hinders the development of new, targeted and more effective treatment strategies. Whilst electrophysiological studies can provide in depth analysis, the possibility of recording electrical activity in large populations of non-neuronal cells remains a significant challenge, even harder to address in the picoAmpere-range, which is typical of cellular level electrical activities. In this paper, we present the measurement and characterization of electrical activity of populations of prostate cancer cells PC-3, demonstrating for the first time a meaningful electrical pattern. The low noise system used comprises a multi-electrode array (MEA) with circular gold electrodes on silicon oxide substrates. The extracellular capacitive currents present two standard patterns: an asynchronous sporadic pattern and a synchronous quasi-periodic biphasic spike pattern. An amplitude of ±150 pA, a width between 50⁻300 ms and an inter-spike interval around 0.5 Hz characterize the quasi-periodic spikes. Our experiments using treatment of cells with Gd³⁺, known as an inhibitor for the Ca²⁺ exchanges, suggest that the quasi-periodic signals originate from Ca²⁺ channels. After adding the Gd³⁺ to a population of living PC-3 cells, their electrical activity considerably decreased; once the culture was washed, thus eliminating the Gd³⁺ containing medium and addition of fresh cellular growth medium, the PC-3 cells recovered their normal electrical activity. Cellular viability plots have been carried out, demonstrating that the PC-3 cells remain viable after the use of Gd³⁺, on the timescale of this experiment. Hence, this experimental work suggests that Ca²⁺ is significantly affecting the electrophysiological communication pattern among PC-3 cell populations. Our measuring platform opens up new avenues for real time and highly sensitive investigations of prostate cancer signalling pathways.

Keywords: PC-3 cells; calcium channel inhibitor; electrical activity; prostate cancer signalling.

Figure 1

(a) Drawing of the transducer used for the culturing of PC-3 cells. PC-3 cells are represented as red circles within the culture medium. (b) PC-3 cells adhered to the gold electrodes 3 days after being deposited. (c) Cell viability describing a typical exponential PC-3 cell growth in the MEA device.

Figure 2

Electrical activity of a PC-3 cells culture on a Si/SiO₂/Au substrate chip. (a) Baseline measured on the chip with only cell medium. (b) Most representative electrical activity of PC-3 cells during the experiment, showing on the left side of the graph the sporadic and mostly unipolar electrical activity. (c) Zoom-in to the sporadic and asynchronous regime showing a typical unipolar negative spike. (d) Quasi-periodic activity of PC-3 cells, presenting Biphasic spikes. (e) Biphasic pulses of the electrical activity of PC-3 cells, with a measurable distance between the positive and the negative pulse of about 0.3 s. (f–h) represent the characterization of the quasi-periodic activity of PC-3 cells: (f) Number of spikes depending on its amplitude. (g) Number of spikes depending on its width. (h) Number of spikes depending on its distance between them. The interspike intervals were distributed into time slots with a resolution of 1 s.

Figure 3

(a) Electrical activity of PC-3 cells culture before, during and after using Gd³⁺ has been used as a Ca²⁺ inhibitor. Before and after the use of Gd³⁺, the electrical activity shows quasi-periodic current oscillations. (b) Number of spikes detected in three different moments: before, during and after the use of the Ca²⁺ inhibitor. (c) Gadolinium chloride MTT assays. The result shows that there is no significant toxicity of GdCl³ in 20 min of incubation. The results of (c) are reported as means ±SEM. The data were analysed by one way ANOVA, p < 0.05, which means there is a significant difference between results of different concentrations (n = 3). Error bars represent standard error with respect to the repeated six measurements of the same concentration. (d) Positive and negative control test of gadolinium chloride. The result shows that there is no significant toxicity of 250 µM GdCl³ in 20 min of incubation compared with negative control (water) and positive control (250 µM triton). The results are reported as means ±SEM. (* p < 0.05, Student’s t-test). There is a significant difference between results of GdCl³ and positive control at 250 µM concentration (n = 3). Error bars represent standard error with respect to the three independent experiments.