Synergistic effects in neuromuscular activation and calcium-sensitization in the bladder trigone

To elucidate possible synergistic effects between adrenergic, muscarinic, and purinergic neuromuscular activation in the bladder trigone, and to examine the relevance of the Rho-kinase (ROCK)/protein kinase C (PKC) pathway as a possible underlying mechanism.

Muscle strips were dissected from the superficial trigone of male guinea-pigs. Contractions were elicited by electrical-field stimulation (EFS: 0.1 ms pulses, 1-64 Hz for 3 s) or exposure to exogenous agonists.

There was evidence for functional adrenergic, purinergic, and muscarinic neurotransmission. Selective inhibition of individual components suggested synergistic interactions. The mean (sd) EFS contractions were enhanced by carbachol (0.3 microm) and phenylephrine (10 microm) to 2.4 (0.4) and 6.4 (1.5)-fold of control (32 Hz), respectively. Phenylephrine (10 microm) also augmented contractions induced by carbachol (1 microm) to 3.9 (1.2)-fold of control, alpha,beta-methylene ATP (1 microm) to 4.3 (0.4) and 20 mm superfusate K(+) to 5.0 (2.0). The PKC inhibitors GF 109203X (5 microm) and H-7 (100 microm), as well as the ROCK inhibitor Y-27632 (5 microm) reduced the phenylephrine contracture to 37.3 (7.4), 38.5 (11.2) and 54.9 (7.8)% of control, respectively. With the exception of H-7 they had no significant effect on the carbachol response.

This study shows a synergistic effect between adrenergic, muscarinic, and purinergic receptor activation on the muscle of the superficial trigone. The study suggests that Ca(2+)-sensitization of contractile proteins plays a key role in this synergism, particularly for adrenergic activation.