Urethral smooth muscle (USM) contracts to generate myogenic tone during bladder filling, thus maintaining urinary continence by preventing urine leakage. Historically, USM physiological investigation has largely utilized mammalian models such as pigs, guinea-pigs and rabbits, which have provided a wealth of information on how different cell types and ionic conductances contribute to USM tone and function. For example, urethral tone was hypothezied to originate from Ca²⁺ influx into USM cells (USMC) via a window current for voltage-dependent L-type Ca²⁺ channels, as drugs such as nifedipine reduced tone in these species. Previous studies from our laboratory identified a population of spontaneously active, non-contractile cells in rabbit USM termed interstitial cells of Cajal-like cells (ICC-LC) which we purported to serve as electrical pacemakers to USMC to control tone (Sergeant et al., 2000). Rabbit ICC-LC exclusively expressed the Ca²⁺-activated-Cl^– channel ANO1, and inhibitors of Ca²⁺-activated-Cl^– channels drastically reduced rabbit urethral tone and contractions evoked by neurotransmitters (Fedigan et al., 2017).

More recently, our laboratory has sought to further elucidate the cell types and ionic conductances that regulate USM contractility using transgenic mouse models, combined with the most up to date pharmacological targeting of ion channels suggested to play a role in USM contractility. Using a genetically encoded Ca²⁺ reporter expressed exclusively in either USMC or ICC-LC, we have been able to characterize the underlying Ca²⁺ signals in USM that generate myogenic tone. Asynchronous Ca²⁺ waves in USMC bundles cause uncoordinated contractions across the sphincter, which summate to generate uniform tone (Drumm et al., 2018). Cell-specific optogenetic reporter mice have allowed us to unambiguously identify and stimulate ICC-LC within intact tissues, allowing us to report, to our surprise, that while ICC-LC are a dynamically active and distinct cell type in the urethra, they do not appear to act as pacemakers nor neuromodulators in mice (Gupta et al., 2024). Furthermore, using our in-situ Ca²⁺ imaging capacity along with potent and specific modulators of ANO1 and L-type Ca²⁺ channels, we have again to our surprise found that neither conductance is required for normal USM Ca²⁺ activity nor contractility, but instead that store-operated Ca²⁺ entry is an essential pathway required for normal USM function (Gupta et al., 2025).

Our research at Dundalk Institute of Technology highlights how the advent of nascent technologies and tools allows us to re-examine conclusions drawn from previous studies and to further advance our understanding of complex physiological processes across different species.