Changes in the normalized volume <i>v</i> = V/V₀ of HEK293 cells in response to sequential application of sucrose and <i>myo</i>-inositol solutions of the same osmolality of 100 mOsm.

<p>The cells were bathed initially (<i>time</i> < ∼30 s) in isotonic growth medium (300 mOsm) and then exposed to a 100-mOsm sucrose solution. The strongly hypotonic sucrose solution (<i>filled symbols</i>) caused fast cell swelling to a transient maximum volume <i>v</i>_max of ∼1.6 within the first 2–3 min. After the initial swelling, the cells underwent RVD, i.e. they gradually shrank to reach the original isotonic volume (<i>v</i>₀ ≈ 1) within ∼20 min in the presence of sucrose. The replacement of sucrose by an equiosmotic amount of <i>myo</i>-inositol (<i>arrows</i>) abolished RVD and caused secondary cell swelling (<i>empty symbols</i>). The rate of secondary swelling (Δ<i>v</i>/Δ<i>t</i>_ino, <i>red fitted lines</i>) decreased with time during and after RVD (7–35 min). The addition of <i>myo</i>-inositol 40 min after hypotonic shock did not cause any significant cell swelling. Each data point represents the mean ± SE of 25–42 individual cells measured in 2–3 independent experiments. For each time point of <i>myo</i>-inositol addition, the rates of RVD Δ<i>v</i>/Δ<i>t</i>_RVD (<i>blue lines</i>) and the rates of secondary swelling Δ<i>v</i>/Δ<i>t</i>_ino (<i>red lines</i>) were determined to calculate the permeability coefficients for myo-inositol <i>P</i>_ino by applying Eqs. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0119990#pone.0119990.e001" target="_blank">1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0119990#pone.0119990.e004" target="_blank">2</a>. The inset illustrates the decay of <i>P</i>_ino with time during RVD.