Data from: A four-component model of the action potential in mouse detrusor smooth muscle cell

Detrusor smooth muscle cells (DSMCs) of the urinary bladder are electrically connected to one another via gap junctions and form a three dimensional syncytium. DSMCs exhibit spontaneous electrical activity, including passive depolarizations and action potentials. The shapes of spontaneous action potentials (sAPs) observed from a single DSM cell can vary widely. The biophysical origins of this variability, and the precise components which contribute to the complex shapes observed are not known. To address these questions, the basic components which constitute the sAPs were investigated. We hypothesized that linear combinations of scaled versions of these basic components can produce sAP shapes observed in the syncytium.

The basic components were identified as spontaneous evoked junction potentials (sEJP), native AP (nAP), slow after hyperpolarization (sAHP) and very slow after hyperpolarization (vsAHP). The experimental recordings were grouped into two sets: a training data set and a testing data set. A training set was used to estimate the components, and a test set to evaluate the efficiency of the estimated components. We found that a linear combination of the identified components when appropriately amplified and time shifted replicated various AP shapes to a high degree of similarity, as quantified by the root mean square error (RMSE) measure.

We conclude that the four basic components - sEJP, nAP, sAHP, and vsAHP - identified and isolated in this work are necessary and sufficient to replicate all varieties of the sAPs recorded experimentally in DSMCs. This model has the potential to generate testable hypotheses that can help identify the physiological processes underlying various features of the sAPs. Further, this model also provides a means to classify the sAPs into various shape classes.

膀胱逼尿平滑肌细胞（Detrusor smooth muscle cells, DSMCs）通过缝隙连接彼此实现电连通，并构成三维合胞体。此类细胞可产生自发电活动，包括被动去极化与动作电位。从单个逼尿平滑肌细胞记录到的自发放电动作电位（spontaneous action potentials, sAPs）形态差异极大，但其变异性的生物物理起源以及构成复杂形态的精确组分仍未明确。为解答上述问题，本研究针对构成自发放电动作电位的基本组分展开探究，并提出假说：对这些基本组分进行缩放后的线性组合，可复现合胞体中观测到的自发放电动作电位形态。

本研究将上述基本组分界定为自发放电诱发接头电位（spontaneous evoked junction potentials, sEJP）、原生动作电位（native AP, nAP）、慢后超极化（slow after hyperpolarization, sAHP）以及极慢后超极化（very slow after hyperpolarization, vsAHP）。实验记录被划分为两组：训练数据集与测试数据集。其中训练集用于估算基本组分，测试集则用于评估所估算组分的有效性。研究结果显示，对已识别组分进行适当放大与时移后的线性组合，可高度复现各类动作电位形态，该结果通过均方根误差（root mean square error, RMSE）量化得以验证。

综上，本研究中识别并分离得到的四类基本组分——sEJP、nAP、sAHP与vsAHP——是复现实验中记录的逼尿平滑肌细胞自发放电动作电位所有形态变体的必要且充分条件。该模型有望生成可检验的假说，助力阐明自发放电动作电位各类特征背后的生理过程。此外，该模型还可实现将自发放电动作电位按不同形态类别进行分类。