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First published online December 26, 2008
Journal of Experimental Biology 212, 270-276 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.023283
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Spontaneous fluctuation of the resting membrane potential in Paramecium: amplification caused by intracellular Ca2+

Yasuo Nakaoka1,2,*, Takafumi Imaji2, Masahiro Hara2 and Noboru Hashimoto3

1 Biophysical Dynamics Laboratories, Graduate School of Frontier Bioscience, Osaka University, Toyonaka, Osaka 560-8531, Japan
2 Division of Biophysical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
3 Division of Integrated Human Sciences, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido 061-0293, Japan


Figure 1
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  		Fig. 1. Simultaneous measurements of the resting potential and intracellular Ca2+ concentration ([Ca2+]i). (A) A composite image from a synchroscope and a fluorescence microscope. Both images from the synchroscope and fluorescence microscope indicate resting potential and [Ca2+]I, respectively, and are joined to form a single image. The bottom right of the fluorescence cellular image is the anterior side of the cell. (B) Fluctuations of resting potential and fluorescence intensity (FI). (i) Fluctuation of resting potential. Time average of membrane potential is shown as zero. (ii) Fluctuation of fluorescence intensity measured across the whole cell area. Fluorescence intensity was normalized using the time average of fluorescence intensity for the whole cell area. Changes from the average are shown. (iii) Fluctuation of fluorescence intensity measured across the anterior half of the cell. Fluorescence intensity was normalized using the time average of fluorescence intensity of the anterior half of the cell. (iv) Fluctuation of fluorescence intensity measured across the posterior half of the cell. Fluorescence intensity was normalized using the time average of fluorescence intensity of the posterior half of the cell. Above data represent data obtained from a single cell.

 

Figure 2
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  		Fig. 2. Effects of Ca2+ inflow on the fluctuations of membrane potential. The fluctuation of membrane potential at the resting level was recorded for 5 min, and a fluctuation histogram from the mean potential level was calculated. (A) Fluctuation of membrane potential and (B) a fluctuation histogram using standard solution as the control. (C) Membrane potential fluctuation and (D) a fluctuation histogram in the presence of 5 µmol l–1 Ruthenium Red. (E) Membrane potential fluctuation and (F) a fluctuation histogram recorded from the anterior fragment of the cell. (G) Membrane potential fluctuation and (H) a fluctuation histogram recorded from the posterior fragment of the cell. Fluctuation amplitudes corresponding to the full width at half maximum (FWHMs) of the distributions are shown on the right side of the histograms.

 

Figure 3
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  		Fig. 3. Effects of [Ca2+]i on the fluctuations of membrane potential. (A) Membrane potential fluctuation and (B) a fluctuation histogram recorded from a cell injected with BAPTA. (C) Membrane potential fluctuation and (D) a fluctuation histogram in the presence of 5 mmol l–1 BaCl2. Fluctuation amplitudes corresponding to the full width at half maximum (FWHMs) of the distributions are shown on the right side of the histograms.

 

Figure 4
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  		Fig. 4. Simulation of membrane potential fluctuations with a computational model as described in Appendix 1. Three cases of Ca2+ sensitivity of ion channels are assumed. The parameter values used in the simulation are given in Appendix 1. (A) Membrane potential fluctuation and (B) a fluctuation histogram in Case I, in which neither K+ nor Ca2+ channels are assumed to have Ca2+ sensitivity. (C) Membrane potential fluctuation and (D) a fluctuation histogram in Case II, in which only K+ channels are assumed to have Ca2+ sensitivity. (E) Membrane potential fluctuation and (F) a fluctuation histogram in Case III, in which both K+ and Ca2+ channels are assumed to have Ca2+ sensitivity. Fluctuation amplitudes corresponding to the FWHMs of the distributions are shown on the right side of the histograms.

 

Figure 5
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  		Fig. 5. Simulation of simultaneous changes of membrane potential and intracellular Ca2+ concentration ([Ca2+]i) for Case III of the computational model as described in Appendix 1. Membrane potential fluctuations {delta}V(t) and fluctuation ratios of intracellular Ca2+ concentration {delta}{rho}i(t) are defined as {delta}V(t){equiv}V(t)–<V(t)> and {delta}{rho}i(t){equiv}[{rho}i(t)–<{rho}i(t)>]/<{rho}i(t)>, respectively, where <V(t)> and <{rho}i(t)> are long time averages of membrane potential V(t) and intracellular Ca2+ concentration {rho}i(t), respectively. Fluctuation ratios of intracellular Ca2+ concentration {delta}{rho}i(t) are indicated as changes in [Ca2+]i in the ordinate.

 

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© The Company of Biologists Ltd 2009