Muscarinic receptor function, density and G‐protein coupling in the overactive diabetic rat bladder

Abstract

1 Bladder smooth muscle sensitivity to muscarinic agonists is increased in the overactive bladder. Treatment of rats with streptozotocin induces a diabetic state in which the bladder muscle is overactive and also supersensitive to muscarinic agonists. This study has examined bladder contraction, muscarinic receptor density and receptor/G-protein coupling in the streptozotocin-induced overactive bladder of the rat. 2 Diabetes was induced by a single intraperitoneal dose of streptozotocin. Seven days later contraction of isolated detrusor muscle strips was assessed in tissue bath experiments, while receptor density was assayed in saturation experiments with [3H]-QNB (quinuclidinyl benzilate, L-[benzilic-4,4'-3H]) and receptor/G-protein coupling was determined in agonist displacement experiments with this radioligand. 3 Isolated detrusor strips from diabetic animals displayed an enhanced degree of spontaneous activity (0.060 +/- 0.016 g mg(-1), compared with 0.015 +/- 0.004 g mg(-1), P < 0.05). Carbachol produced contractile responses in tissues from both control and diabetic rats, but the diabetic tissues were more sensitive to this agonist, the pEC50 being 6.52 +/- 0.17 compared with 5.93 +/- 0.06 in controls (P < 0.001). Maximum responses to carbachol were similar in both groups of animals. The increase in carbachol potency was accompanied by a 40% increase in receptor density from 158 +/- 5 to 221 +/- 22 fmol mg(-1) protein (P < 0.05), but this was not enough to fully account for the change in tissue sensitivity. 4 In the absence of GTP-gamma-S, carbachol displaced [3H]-QNB from two binding sites, the high-affinity site (pKi = 7.06 +/- 0.26) which represents the receptors coupled to G-proteins made up 43.1 +/- 5.9% of the total binding sites in control tissues and this value was similar (41.0 +/- 4.0%) in the diabetic tissues (pKi = 6.64 +/- 0.31). In the presence of GTP-gamma-S, carbachol displaced [3H]-QNB from a single binding site which had a low-affinity, similar to the low-affinity site observed in the absence of GTP-gamma-S. 5 These data demonstrate that detrusor supersensitivity is observed after only 1 week of untreated diabetes in the rat. The overactivity is associated with an enhanced sensitivity to carbachol, which is partly explained by an increase in receptor density, but there appears to be no change in receptor/G-protein coupling.

Glucose-Dependent Enhancement of Diabetic Bladder Contraction Is Associated with a Rho Kinase-Regulated Protein Kinase C Pathway

“…Mechanisms governing the enhancement of contractions have been suggested in the SHR. An increase in the total number of muscarinic receptors and/or the level of sensitization of the receptor induced the dysfunction (Sherer et al, 2000;Stevens et al, 2006). In addition, bladder dysfunction in the absence of alterations of muscarinic receptor was also documented (Schneider et al, 2005).…”

Diabetes mellitus- and cooling-induced bladder contraction: an in vitro study

“…Kamata et al (1992) have also shown that the enhanced contractile response to ACh in detrusor strips of urinary bladders from STZ-induced diabetic rats were associated with an increased population of muscarinic receptors. Furthermore, the overactivity was characterized by an enhanced sensitivity to carbachol, partly due to an increase in receptor density, but without change in receptor/G-protein coupling (Hampel et al, 2003;Mumtaz et al, 2006;Stevens et al, 2006).…”

Muscarinic Receptor Subtypes in the Lower Urinary Tract

“…Denervation and decentralization induce super-sensitivity to cholinergic stimuli, as been observed in the rat bladder [109] , which also occurs after capsaicin treatment [110] . In the denervated rat bladder Color version available online and in the bladder of spinal cord-injured rats, the expression of muscarinic M 2 receptors increases [111][112][113] , while, in diabetic rats, a super-sensitivity to cholinergic stimuli occurs concomitantly with increments in muscarinic receptor density and in muscarinic M 3 receptor expression [114][115][116] . Modulations in the cholinergic bladder contraction also occur during cystitis [78,108] .…”