Hypothesis / aims of study
Acid-sensing ion channel (ASIC) is a member of sodium channel superfamily including the epithelial sodium channel/degenerin (ENaC/DEG) that play crucial roles in mechanosensation, chemosensation, and nociception. ASIC is composed of 5 subunits, ASIC1, ASIC2, ASIC3, ASIC4, and ASIC5; and ASIC1 and ASIC2 have ‘a’ and ‘b’ forms . Previous study revealed that genes of ASIC subunits are largely expressed in the mouse urinary bladder (i.e., detrusor and bladder mucosa) and L6/S1 dorsal root ganglia (DRGs) innervating the bladder, suggesting the possibility that ASICs are involved in modulation of lower urinary tract (LUT) function . Furthermore, the study showed that the total amounts of ASIC genes which are expressed in the bladder and the DRGs are more than those of TRPV1 genes in mice. A-317567 is a potent ASIC3 inhibitor, which has been reported to exert antidepressant and antinociception effects. We conducted this study using A-317567 to determine whether ASIC3 play a functional role in control of LUT activity.
Study design, materials and methods
Female C57BL/6 mice (12-14 week-old) were used. The animals were anesthetized with sevoflurane during surgery including precollicular decerebration. A low midline abdominal incision was made, and a PE-50 tube was inserted into the bladder dome to record intravesical pressure. Cystometrogram (CMG) recordings conducted under unanesthetized conditions were started 2 h after decerebration, by continuously infusing saline (pH 6.3; infusion rate: 30 µl/min) at room temperature. CMG parameters evaluated were: maximal voiding pressure (MVP) and inter-contraction interval (ICI). A-317567 was dissolved in physiological saline adjusted to pH 2.8 and pH 6.0 with 1 N sodium hydroxide for i.p. injection (100 mM) and intravesical perfusion (100 µM), respectively. A-317567 was also dissolved in dilute acetic acid (A/A, pH 3.0) for intravesical perfusion (100 µM), to examine the drug effects on the bladder hyperactivity during irritation of LUT. The dose for i.p. injection was 30 μmol/kg; the dose was chosen because it has been shown to produce marked analgesic effects in previous study . Effects of A-317567 were compared with those of the vehicle. All values are expressed as mean ± S.E.M. Statistical analysis was made using repeated measures two-way ANOVA followed by Sidak's multiple comparisons test when applicable. P < 0.05 was considered significant.
I.p. injection of A-317567 increased ICI by 30 % during saline infusion CMG, whereas it had no effects on MVP (***P < 0.001) (Table 1a). The drug ameliorated an aberrance in urine storage such as bladder hyperactivity induced by intravesical A/A perfusion, increasing ICI by 70 % (****P < 0.0001) (Table 1b). The effect only lasted for less than 10 min. The i.p. dose produced no changes in MVP (i.e., during bladder contraction period). The vehicle i.p. injection did not produce any effects on either normal LUT activity (during saline infusion) or A/A-induced bladder hyperactivity.
Intravesical perfusion of A-317567 (100 µM) had no effects on bladder activity with or without A/A irritation (i.e., pH3.0 or pH6.0) to the LUT (Table 2a,b).
Interpretation of results
ASIC3 is involved in afferent signal transduction of reflex bladder activity under conditions of the LUT either with or without acid irritation, showing a contribution to urine storage function; whereas it does not participate in modulation of bladder contractility (i.e., efferent modulation). The systemic injection of A-317567 exhibited a short duration in the action. Meanwhile, ASIC3 blocker given intravesically did not change the LUT activity either with or without acid irritation.