Most of my other articles are from my PhD research in cell biology where I looked at the way cell growth was controlled. Normal cells stop growing after they reached a certain density, but cancer involves a los of control of this growth inhibition. I looked at the elektrophysiological aspects of this phenomomen: calcium concentrations, membrane potential and electrical coupling. 

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de Roos ADG, Willems PH, Peters PH, van Zoelen EJ, Theuvenet AP (1997) Synchronized calcium spiking resulting from spontaneous calcium action potentials in monolayers of NRK fibroblasts. Cell Calcium 22:195-207.

de Roos ADG, Willems PH, van Zoelen EJ, Theuvenet AP (1997) Synchronized Ca2+ signaling by intercellular propagation of Ca2+ action potentials in NRK fibroblasts. Am J Physiol 273:C1900-7.

When I was doing initial calcium measurements with a fluorimeter, in which calcium was measured in a large number of cells simulatneously, I noticed large regular fluctuations that had to be synchronized in all cells. When we looked at the single cell level, we could confirm this (in collaboration with Peter Willems), but we had initially no idea how this happened because it was too fast to be due to diffusion-mediated calcium-induced calcium release. Interestingly, I found a similar phenomenon when I did membrane potential measurements using patch clamp, where I saw spike-like calcium increases. A comparison with the literature suggested that they may be calcium action potential, which was also met by incredulance by many. I set out to investigate this and confirmed that they were calcium action potential, a new finding in fibroblasts of unknow importance. I suspect that fibroblasts have a function in synchronizing responses in large numbers of cell. Another example of how serendipity and out-of-the-box thinking may lead to fruitful research.

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de Roos ADG, Van Zoelen EJ, Theuvenet AP (1997) Membrane depolarization in NRK fibroblasts by bradykinin is mediated by a calcium-dependent chloride conductance. J Cell Physiol. 1997 170:166-73.

Not one of my most interesting articles because it is mainly descriptive, but it did form the basis for further research in the actions of bradykinin and other growth factors. These molecules are able to induce density-independent cell growth, a model for cancer formation. Also it combined various cell physiological measurements.

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de Roos ADG, van Zoelen EJ, Theuvenet AP (1996) Determination of gap junctional intercellular communication by capacitance measurements. Pflugers Arch 431:556-63.

My first first-authorship and the first article of my PhD research. I was working on monolayers of fibroblasts and we found that they were electrically well connected. All cells have a certain capacitance (like an electrical capacitor) that can be measured by determining the decaying current response after a voltage step, representing the charging (and uncharging) of the cell. I found that when I applied a voltage step to one cell that was lying next to another cell, the reponse was twice as big, and I could see this effect up to ten or twenty cells. This indicates that fibroblasts were able to form an electrical syncytium. I remember that when I proposed these kind of experiments to experts in the field of electrophysiolgy they dismissed this possibility a priori. It turned out not to be the first time that my proposals were initially ridiculed but turned out to be true. Luckily, my PhD project leaders Lex Theuvenet and Joop van Zoelen were more open-minded than the rest and it proved to be a succesful start of my PhD research.