Frusemide potentiates acetylcholine and carbachol in contracting the rat urinary bladder

Identification by virtual screening and functional characterisation of novel positive and negative allosteric modulators of the α7 nicotinic acetylcholine receptor

Several previous studies have demonstrated that the activity of neurotransmitters acting on ligand-gated ion channels such as the nicotinic acetylcholine receptor (nAChR) can be altered by compounds binding to allosteric modulatory sites. In the case of α7 nAChRs, both positive and negative allosteric modulators (PAMs and NAMs) have been identified and have attracted considerable interest. A recent study, employing revised structural models of the transmembrane domain of the α7 nAChR in closed and open conformations, has provided support for an inter-subunit transmembrane allosteric binding site (Newcombe et al 2017). In the present study, we have performed virtual screening of the DrugBank database using pharmacophore queries that were based on the predicted binding mode of PAMs to α7 nAChR structural models. A total of 81 compounds were identified in the DrugBank database, of which the 25 highest-ranked hits corresponded to one of four previously-identified therapeutic compound groups (carbonic anhydrase inhibitors, cyclin-dependent kinase inhibitors, diuretics targeting the Na⁺-K⁺-Cl^- cotransporter, and fluoroquinolone antibiotics targeting DNA gyrase). The top-ranked compound from each of these four groups (DB04763, DB08122, furosemide and pefloxacin, respectively) was tested for its effects on human α7 nAChR expressed in Xenopus oocytes using two-electrode voltage-clamp electrophysiology. These studies, conducted with wild-type, mutant and chimeric receptors, resulted in all four compounds exerting allosteric modulatory effects. While DB04763, DB08122 and pefloxacin were antagonists, furosemide potentiated ACh responses. Our findings, supported by docking studies, are consistent with these compounds acting as PAMs and NAMs of the α7 nAChR via interaction with a transmembrane site.

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Identification of α7 nAChR positive and negative allosteric modulators.

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Furosemide is a positive allosteric modulator of α7 nAChRs.

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DB04763, DB08122 and pefloxacin are negative allosteric modulators of α7 nAChRs.

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Modulation of α7 nAChRs by an allosteric transmembrane site.

Temporal changes in rabbit urinary bladder function and DNA synthesis during chronic treatment with furosemide

In a preliminary study we showed that 14 days of furosemide infusion in rabbits caused increases in bladder mass and contractile responses of bladder body strips to field stimulation, bethanechol, ATP and KCl. The present study investigated the temporal effects of furosemide-induced diuresis on micturition, bladder mass, bladder wall proliferation activity and DNA synthesis. In addition, contractile responses of bladder body strips were monitored. Furosemide-containing osmotic pumps were implanted in male New Zealand White rabbits. Micturition was monitored for 7 days. Biochemical analyses were done 3, 7 and 14 days after implantation. Contractile responses were measured at 3 and 7 days. Polyuria and polydipsia started within 1 day after implantation of furosemide-containing osmotic pumps and continued at the same level for 7 days. Bladder mass was significantly increased at 3 and 7 days. Diuresis stimulated 3H-thymidine uptake and caused an increase in bladder DNA concentration at 3 days. However, both DNA concentrations and 3H-thymidine levels returned to control levels by 7 days. Contractile responses to field stimulation and agonists were increased at 7 days but unchanged at 3 days. The data confirm that modest increases in bladder mass and the ensuing increases in contractile function are a normal and beneficial physiological response to diuresis.