Changes in the distribution of different subtypes of P2X receptor clusters on smooth muscle cells in relation to nerve varicosities in the pregnant rat urinary bladder

Clusters of purinergic receptor subunits, about 1 mum diameter, are found on the smooth muscle cell membrane beneath junctional varicosities in the detrusor muscle of the rat urinary bladder. We have examined the extent of redistribution of the six different subunit clusters, P2X(1) to P2X(6), with respect to junctional varicosities during pregnancy, as it is known that the detrusor muscle undergoes changes in purinergic innervation during this period. Before pregnancy, clusters at junctional varicosities are principally composed of the subtypes P2X(1), P2X(2), P2X(3) and P2X(5). However this subtype distribution changes dramatically during pregnancy, such that by day 14 of pregnancy, the extent of P2X(1), P2X(2), P2X(3) and P2X(5) junctional clusters has decreased by more than 80% whereas the extent of P2X(4) and P2X(6) junctional clusters has increased by more than 80%. These changes were confirmed with Western blots for different subtypes. It is suggested that the changes in the purinergic innervation of the detrusor muscle during pregnancy reflect changes in the P2X subtypes found on the smooth muscle membrane beneath junctional varicosities.