A QUANTITATIVE ANALYSIS OF PURINOCEPTOR EXPRESSION IN HUMAN FETAL AND ADULT BLADDERS

Abstract

In adults there is evidence that adenosine triphosphate acting at P2X receptors functions as a co-transmitter at vesical smooth muscle. The contractile mechanisms of human fetal bladder have been studied to a limited extent and it remains undetermined whether P2X receptors contribute. We compared the expression of the 7 known P2X receptors in fetal and adult human bladders using a quantitative polymerase chain reaction (PCR) based method. Real-time quantitative reverse transcriptase-PCR provides a system for the detection and analysis of RNA. Four complete cadaver fetal bladders were obtained at 16 weeks to full-term gestation and divided into a total of 12 segments. Adult bladder samples were obtained from 4 patients 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 genes in total RNA. In adult bladders P2X1 was by far the predominant purinergic receptor at the messenger RNA level. The remaining purinergic receptors were consistently present in the order P2X1 >> P2X4 > P2X7 >> P2X5 > P2X2 >> P2X3 = P2X6 = 0. In fetal bladders the expression of P2X1 transcripts was much lower than in adult bladders, and P2X4 and P2X7 were also present. The rank order of the P2X transcript level was P2X1 = P2X4 > P2X7 >> P2X5 >> P2X2 >> P2X3 = P2X6 = 0. With increasing gestation the P2X receptor transcript level (expression) shifted from the dome to the body of the bladder. P2X1 is the predominant purinoceptor subtype in adult human bladders, consistent with pharmacological evidence. The fetal expression of all P2X receptor transcripts is much lower than in adults, suggesting that purinergic transmission is of less importance. However, there are also several 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 of purinoceptors. These changes are likely to reflect the changing role of purinergic transmission in the control of bladder motility during fetal maturation.