Spatial distribution and developmental appearance of postjunctional P2X(1)receptors on smooth muscle cells of the mouse vas deferens

P2X(1)-type purinoceptors, have been shown to mediate fast transmission bet ween sympathetic varicosities and smooth muscle cells in the mouse vas defe rens but the spatial organization of these receptors on the smooth muscle c ells remains inconclusive. Voltage clamp techniques were used to estimate t he amplitudes of spontaneous excitatory junction currents (SEJCs) in cells of the vas deferens longitudinal smooth muscle layer. These currents involv ed the activation of about 6% of the P2X-type channels present on the cell, as compared to whole cell currents produced when isolated smooth muscle ce lls were exposed to maximal concentrations of either ATP or alpha,beta -MeA TP. Immunofluorescence staining of the vas deferens with antibodies against P2X(1) receptor showed a diffuse, grainy distribution over the entire memb rane of each smooth muscle cell. Anti-P2X(1) staining was not markedly clus tered beneath anti-SV2-stained sympathetic varicosities. Similar results we re obtained for cells in the urinary bladder. During development, P2X(1) mR NA was detected as early as embryonic day 15 (E15). Increasing intensities of diffuse immunostaining for P2X(1) were observed in the walls of the blad der, tail artery, and aorta from E15 until 6 weeks postnatal. The vas defer ens showed increasing intensities of diffuse staining of its smooth muscle layers between 2 and 6 weeks postnatal, consistent with the time-course of development of fast purinergic transmission described previously. Together, the results suggest that the response of smooth muscle of the vas deferens to ATP released from sympathetic varicosities relies on rapidly desensitiz ing P2X(1) receptors, distributed diffusely across the smooth muscle cell s urface. Synapse 42:1-11, 2001. (C) 2001 Wiley-Liss, Inc.