Supplemental Information

PKD2L1/PKD1L3 Channel Complex with an Alkali-activated mechanism and Calcium-dependent Inactivation

Peihua Chen, Jinzhi Wu, Jie Zhao, Ping Wang, Jianhong Luo, Xiao-dong Liu and Wei Yang

I. Computational model of PKD2L1-1L3 channel

General scheme

Hodgkin-Huxley-type models were applied to quantify the ionic currents obtained from whole cell patch-clamp experiments. A nonlinear least-squares algorithm in Matlab was used to fit the recordings for parameter estimation. The model of PKD2L1-1L3 was created on the NEURON softwareplatform (Hines and Carnevale, 2001).

Currents through PKDL channels,IPKD

PKDais the activation parameter and PKDi is inactivation parameter of PKDL channels. [Ca2+]odenotes the Ca2+ concentration inextracellular space. GPKDand EPKD are the maximum conductance of PKDL channels and the reversal potential, respectively.

EPKD=0 mV; GASIC=0.0035S/cm2

Alkali-activated model

;

Acid-activated model

;

II. Single-channel kinetic model of PKD2channels

Based onsingle-channel recordings of PKD2 channels(Gonzalez-Perrett et al., 2002), two open states (O1 and O2)and two closed states (C1 and C2)were constructed as shown in the kinetic scheme. In addition, the time-constants of these four states were calculated from histograms of open and closed dwell-time, shown in Table S2. The rate constants between two adjacent states,knm (n, m=1, 2, 3, and 4), were calculated from the time-constants of dwell-time (τ).

, , , ;

The macroscopic current can be calculated as follows:

where g is the single channel conductance and Erev is the reversal potential. PO2 and PO3 are the fractions of channels staying at the states O2 and O3, respectively; and can be described as:

Knmbased on single-channel recordings can be defined as:

To model single channels in QuB, the above equations were simplified as:

To validate the model, the parameters between modeling and experiments are compared in Table S2.

Time Constant (Dwell Time) / τC1(ms) / τO2(ms) / τO3(ms) / τI4(ms) / pH
Experiment / 44.4 / 1.78 / 16.7 / 0.79 / 6.4
Simulation / 44.4 / 1.76 / 12.4 / 0.79
Experiment / 0.56 / 14.8 / 3.55 / 5.39 / 7.14
Simulation / 0.56 / 17.6 / 6.17 / 5.38

Table S1. Closed andopen dwell-time forexperimental data and the single-channel model

For single-channel recordingexperiments, time-constants corresponding to each state wereobtained from the closed and open dwell histograms in Figs2 and 3 (Gonzalez-Perrett et al., 2002). Dwell time constants for single-channel simulation were calculated from knm equations for each pH.

References

Gonzalez-Perrett, S., Batelli, M., Kim, K., Essafi, M., Timpanaro, G., Moltabetti, N., Reisin, I.L., Arnaout, M.A., and Cantiello, H.F. (2002). Voltage dependence and pH regulation of human polycystin-2-mediated cation channel activity. J Biol Chem 277, 24959-24966.

Hines, M.L., and Carnevale, N.T. (2001). NEURON: a tool for neuroscientists. Neuroscientist 7, 123-135.

Immke, D.C., and McCleskey, E.W. (2003). Protons open acid-sensing ion channels by catalyzing relief of Ca2+ blockade. Neuron 37, 75-84.

Chen P. et. al., 2014

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