Interaction between muscarinic receptor subtype signal transduction pathways mediating bladder contraction

Area of Science:

• Pharmacology
• Urology
• Physiology

Background:

• Muscarinic receptors, specifically M(3), typically control smooth muscle contraction.
• In denervated rat bladders, M(2) receptors also contribute to contraction, as indicated by low affinities of M(3)-selective antagonists.
• The role of M(2) receptors in denervated bladders appears contradictory, suggesting a potential interaction with M(3) receptors.

Purpose of the Study:

• To investigate the interaction between M(2) and M(3) muscarinic receptors in mediating cholinergic contractions.
• To determine if M(2) and M(3) receptors interact synergistically or additively in normal versus denervated rat bladders.

Main Methods:

• Measurement of inhibitory potencies of combined M(2)-selective (methoctramine) and M(3)-selective (p-F-HHSiD) antagonists.
• Assessment of these combinations in normal and denervated rat bladder tissues.
• Utilizing thapsigargin, a sarcoplasmic reticulum ATPase inhibitor, to mimic denervation effects in normal tissue.

Main Results:

• In normal bladders, the combined antagonists showed additive effects, indicating independent receptor pathways.
• In denervated bladders, specific ratios (10:1 and 1:1 methoctramine:p-F-HHSiD) of antagonists exhibited synergistic effects.
• Thapsigargin treatment in normal bladders induced synergistic effects similar to denervated bladders.

Conclusions:

• Both M(2) and M(3) muscarinic receptors can independently induce contraction in normal rat bladders.
• In denervated rat bladders, M(2) and M(3) receptors interact in a facilitatory manner to mediate cholinergic contractions.
• This interaction in denervated bladders may involve calcium signaling pathways affected by sarcoplasmic reticulum dysfunction.