The single-channel properties of purinergic P2X ATP receptors in outside-out patches from rat hypothalamic paraventricular parvocells.

The aim of this study was to characterize functionally the single-channel properties of rat hypothalamic paraventricular medial parvocell purinergic P2X receptors. Single-channel recordings were made from outside-out patches from coronal whole-brain slices from 4-day-old-rats. A heterogeneous population of functional P2X receptors were observed, possibly reflecting a mixture of homomeric P2X2 receptors and heteromers containing P2X2, P2X3, P2X4 or P2X6 subunits. "Flickery" P2X receptor channels with a high open probability (Po) and chord conductances of 14.4+/-1.75 and 29.6+/-0.5 pS at -80 mV were observed in nine patches. The mean open time was 2.51+/-1.30 ms. In the presence of 1 mM ATP, and excluding long periods of apparent desensitization, these channels had a mean Po of 0.58+/-0.29. "Non-flickery" P2X receptors with chord conductances of 16.9+/-3.48 and 32.4+/-3.75 pS, a mean open time of 0.63+/-0.15 ms and a mean Po of 0.01+/-0.004 at -80 mV were observed in the presence of 1 mM ATP in three patches. P2X receptors showed little apparent concentration dependence in their activity at ATP concentrations of 0.01-1 mM, probably reflecting considerable desensitization. The mean Po (for all data records) at 10 microM was 0.030+/-0.017 and 0.030+/-0.028 at 1 mM.