Accounting for variability in ion current recordings using a mathematical model of artefacts in voltage-clamp experiments

Abstract

Mathematical models of ion channels, which constitute indispensable components of action potential models, are commonly constructed by fitting to whole-cell patch-clamp data. In a previous study we fitted cell-specific models to hERG1a (Kv11.1) recordings simultaneously measured using an automated high-throughput system, and studied cell-cell variability by inspecting the resulting model parameters. However, the origin of the observed variability was not identified. Here we study the source of variability by constructing a model that describes not just ion current dynamics, but the entire voltage-clamp experiment. The experimental artefact components of the model include: series resistance, membrane and pipette capacitance, voltage offsets, imperfect compensations made by the amplifier for these phenomena, and leak current. In this model, variability in the observations can be explained by either cell properties, measurement artefacts, or both. Remarkably, by assuming that variability arises exclusively from measurement artefacts, it is possible to explain a larger amount of the observed variability than when assuming cell-specific ion current kinetics. This assumption also leads to a smaller number of model parameters. This result suggests that most of the observed variability in patch-clamp data measured under the same conditions is caused by experimental artefacts, and hence can be compensated for in post-processing by using our model for the patch-clamp experiment. This study has implications for the question of the extent to which cell-cell variability in ion channel kinetics exists, and opens up routes for better correction of artefacts in patch-clamp data.

Calibration of ionic and cellular cardiac electrophysiology models

“…Another source of problems is lack of control over the experimental system. For example, there are several factors in voltage‐clamping that can cause a difference between the intended and the true membrane potential (Lei, Clerx, Whittaker, et al, ; Neher, ; Sherman et al, ; White, Sekar, & Kay, ). Similarly, intracellular ion concentrations are often assumed to be set by the pipette concentrations, but can vary in nontrivial ways (Mathias, Cohen, & Oliva, ), which will also affect calculated estimates of reversal potentials.…”

“…Some simple measures can be taken, for example, Clerx, Collins, and Volders () modified the identifiability analysis by Fink and Noble () to omit parts of the data routinely “cut out” of current recordings to avoid capacitative artifacts. But in general a more complex approach will be required, including modeling the origins of experimental artifacts as was recently demonstrated in Lei, Clerx, Whittaker, et al (). In this respect it is interesting to notice that any compensation for noise or artifacts carried out experimentally introduces new parameters into the statistical noise model (see Section 2.4), which may then need to be estimated.…”

“…It is often difficult to establish whether discrepancy between model fits or predictions and data is due to experimental artifacts/limitations, model discrepancy, or both (Lei, Clerx, Whittaker, et al, ). Characterizing the size and consequences of model discrepancy is a major and fundamental challenge for our field as predictions begin to be used in safety‐critical settings.…”

Computer modeling of whole-cell voltage-clamp analyses to delineate guidelines for good practice of manual and automated patch-clamp

“…Interpretation of voltagedependence of activation can further be hindered in cases where treatments of interest alter the current amplitude ( Figure 8). A similar mathematical model, taking into account the R S impact has been used to study the causes of variability of current recordings obtained from the voltage-gated potassium channel K v 11.1 (Lei et al, 2019). Here we used such a model to provide a guideline focusing on parameters that the manipulator can easily act on: current amplitude and R S .…”