ATP induced-relaxation in the mouse bladder smooth muscle

Area of Science:

• Physiology
• Pharmacology
• Urology

Background:

• Adenosine triphosphate (ATP) is a key signaling molecule in smooth muscle.
• Its role in urinary bladder function, particularly calcium-force dynamics, requires further elucidation.

Purpose of the Study:

• To investigate the effects of exogenous and endogenous adenosine triphosphate (ATP) on intracellular calcium ([Ca2+]i) and force in mouse urinary bladder smooth muscle.
• To characterize the purinergic receptors involved in ATP-mediated responses.

Main Methods:

• Measurements of intracellular calcium concentration ([Ca2+]i) using fura-2 fluorescence.
• Assessment of smooth muscle force development in intact mouse urinary bladder strips.
• Pharmacological characterization using ATP analogues and a P1-purinoceptor antagonist (8-phenyltheophylline).

Main Results:

• Exogenous ATP caused a significant increase in [Ca2+]i with minimal force, indicating Ca(2+)-force dissociation.
• Electrical stimulation released endogenous neurotransmitters, inducing transient contraction followed by relaxation.
• ATP-induced relaxation was mediated by P2Y purinoceptors, as evidenced by analogue potency (2-MeSATP > ATP > beta gamma Me-ATP) and lack of inhibition by a P1 antagonist.

Conclusions:

• ATP exhibits both activating and relaxing effects on mouse urinary bladder smooth muscle.
• The relaxant effect, mediated via P2Y purinoceptors, is the dominant action and explains ATP's low contractile potency in this tissue.