Functional changes in bladder tissue from type III collagen-deficient mice.

OBJECTIVE: Collagen fibers impart tensile strength and transfer tension from bladder smooth muscle cells. We have previously shown that fibrotic bladders are characterized by an increased type III:type I collagen ratio. To determine the effect of decreased type III collagen on bladder function, type III collagen-deficient mice (COL3A1) were studied physiologically.
METHODS: Bladders from wild-type (+/+) and heterozygous (+/-) COL3A1 mice were biochemically characterized to determine total collagen (hydroxyproline analysis) and collagen subtype concentration (cyanogen bromide digestion and ELISA). Alterations in collagen fiber diameter were assessed by electron microscopy. Bladder muscle strips were used to assess physiologic function.
RESULTS: Hydroxyproline content decreased in heterozygous bladders, which had 50% less type III collagen. Wild-type bladders had a biphasic distribution of collagen fiber sizes, whereas heterozygous bladder collagen fibers spanned a broad range. Physiologically, there were no differences in contractile responses between wild-type and heterozygotes when stimulated with ATP, carbachol or KCl, indicating normal contraction via purinergic and muscarinic receptors, and in response to direct membrane depolarization. In contrast, tension generation in heterozygotes was decreased after field stimulation (FS), indicating decreased synaptic transmission. Length-tension studies showed that the heterozygote muscle strips generated less tension per unit length, indicating that they were more compliant than wild-type controls.
CONCLUSIONS: Critical levels of type III collagen appear to be a requirement for normal bladder tension development and contraction. Our data show that a decrease in the type III:type I collagen ratio, and altered fiber size, results in a more compliant bladder with altered neurotransmitter function.