Spontaneous purinergic neurotransmission in the mouse urinary bladder

Abstract

Spontaneous purinergic neurotransmission was characterized in the mouse urinary bladder, a model for the pathological or ageing human bladder. Intracellular electrophysiological recording from smooth muscle cells of the detrusor muscle revealed spontaneous depolarizations, distinguishable from spontaneous action potentials (sAPs) by their amplitude (< 40 mV) and insensitivity to the L-type Ca 2+ channel blocker nifedipine (1 μm) (100 ± 29%). Spontaneous depolarizations were abolished by the P2X 1 receptor antagonist NF449 (10 μm) (frequency 8.5 ± 8.5% of controls), insensitive to the muscarinic acetylcholine receptor antagonist atropine (1 μm) (103.4 ± 3.0%), and became more frequent in latrotoxin (LTX; 1 nm) (438 ± 95%), suggesting that they are spontaneous excitatory junction potentials (sEJPs). Such sEJPs were correlated, in amplitude and timing, with focal Ca 2+ transients in smooth muscle cells (measured using confocal microscopy), suggesting a common origin: ATP binding to P2X 1 receptors. sAPs were abolished by NF449, insensitive to atropine (126 ± 39%) and increased in frequency by LTX (930 ± 450%) suggesting a neurogenic, purinergic origin, in common with sEJPs. By comparing the kinetics of sAPs and sEJPs, we demonstrated that sAPs occur when sufficient cation influx through P2X 1 receptors triggers L-type Ca 2+ channels; the first peak of the differentiated rising phase of depolarizations -attributed to the influx of cations through the P2X 1 receptor -is of larger amplitude for sAPs (2248 mV s −1 ) than sEJPs (439 mV s −1 ). Surprisingly, sAPs in the mouse urinary bladder, unlike those from other species, are triggered by stochastic ATP release from parasympathetic nerve terminals rather than being myogenic.

Aging differentially modifies agonist-evoked mouse detrusor contraction and calcium signals

“…A recent report in mouse bladder shows that P2X receptors mediate spontaneous muscle depolarization independently of voltage-activated Ca 2+ influx (Young et al 2008). This activity could be related to the spread of depolarization along bundles of cells, a pattern which is thought to actively accommodate the wall tension to the increasing volume of bladder during the filling phase (Hashitani et al 2001).…”

Altered Caveolar Mediated Purinergic Signaling in Spontaneously Hypertensive Rats with Detrusor Overactivity

“…However, a similar effect was described in vasa rectal pericytes, where vasoconstriction was generated not only by purinergic agonists but also after administration of purinergic receptor antagonists, 27 suggesting tonic nucleotide mediated vasodilation. In the bladder stochastic ATP release from parasympathetic fibers was described, 28 which could activate purinergic receptors presynaptically or postsynaptically to modulate SA. Although the mechanism by which P2X1R suppresses SA requires further investigation, our data suggest a physiologically relevant process that Counterstaining with membrane marker wheat germ agglutinin Alexa Fluor 647 conjugate (blue areas) confirmed membrane distribution of spots (Cav-1ϩP2X1).…”

The purinergic neurotransmitter revisited: A single substance or multiple players?

“…For example, local Ca 2+ transients that were resistant to atropine but were inhibited by P2X receptor desensitization with α,β-methylene ATP or by suramin are proposed to be elementary signals of ATP release from nerve varicosities (Heppner et al, 2005). Spontaneous EJPs that are mediated by P2X1 receptors are used to characterize neurogenic release of ATP in the mouse urinary bladder (Young et al, 2008). The purinergic pathway appears to play a greater role at lower stimulation frequencies (Werner et al, 2007).…”