Abstract
Background and hypothesisDetrusor 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.Methods and resultsThe 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.ConclusionsWe 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.
Highlights
The detrusor smooth muscle (DSM) located in the mammalian urinary bladder wall controls the bladder tone, aiding the storage and micturition of urine
The basic components were identified as spontaneous evoked junction potentials, native AP, slow after hyperpolarization and very slow after hyperpolarization
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
Summary
The detrusor smooth muscle (DSM) located in the mammalian urinary bladder wall controls the bladder tone, aiding the storage and micturition of urine. DSM cells (DSMCs) are electrically connected to one another via gap junctions and form a three dimensional electrical syncytium [1,2,3,4,5,6]. Single axon supplies multiple DSMCs and several axons can excite the same DSMC Due to this many-to-many mapping of the DSMCs and the neurotransmitter release sites, and due to the electrically interconnected DSM syncytium, the DSMCs exhibit complex electrical activity. Detrusor smooth muscle cells (DSMCs) of the urinary bladder are electrically connected to one another via gap junctions and form a three dimensional syncytium. 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
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