A quantitative analysis of purinoceptor expression in human fetal and adult bladders

Purpose: In adults there is evidence that adenosine triphosphate acting at P2X receptors functions as a co-transmitter at vesical smooth muscle. The c ontractile mechanisms of human fetal bladder have been studied to a limited extent and it remains undetermined whether P2X receptors contribute. We co mpared the expression of the 7 known P2X receptors in fetal and adult human bladders using a quantitative polymerase chain reaction (PCR) based method . Materials and Methods: Real-time quantitative reverse transcriptase-PCR pro vides a system for the detection and analysis of RNA. Four complete cadaver fetal bladders were obtained at 16 weeks to full-term gestation and divide d into a total of 12 segments. adult bladder samples were obtained from 4 p atients requiring bladder biopsy. Total RNA was extracted from each sample and 10 ng, were used for individual PCR reactions. an ABI 7700 machine (PE Applied Biosystems, California) determined expression levels of the 7 P2X g enes in total RNA. Results: In adult bladders P2X1 was by far the predominant purinergic recep tor at the messenger RNA level. The remaining purinergic receptors were con sistently present in the order P2X1 >> P2X4 > P2X7 >> P2X5 > P2X2 >> P2X3 = P2X6 = 0. In fetal bladders the expression of P2X1 transcripts was much lo wer than in adult bladders, and P2X4 and P2X7 were also present. The rank o rder of the P2X transcript level was P2X1 = P2X4 > P2X7 >> P2X5 >> P2X2 >> P2X3 = P2X6 = 0. With increasing gestation the P2X receptor transcript leve l (expression) shifted from the dome to the body of the bladder. Conclusions: P2X1 is the predominant purinoceptor subtype in adult human bl adders, consistent with pharmacological evidence. The fetal expression of a ll P2X receptor transcripts is much lower than in adults, suggesting that p urinergic transmission is of less importance. However, there are also sever al marked developmental changes in purinoceptor expression in the bladder, in that P2X4 is expressed in developing bladders at relatively high levels. There is also a marked developmental change in the regional distribution o f purinoceptors. These changes are likely to reflect the changing role of p urinergic transmission in the control of bladder motility during fetal matu ration.