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 P2X(2) receptors and heteromers containing P2X(2), P2X(3), P2X(4) or P2X(6) subunits. "Flickery" P2X receptor channels with a high open probability (P-0) 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 P-0 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 P-0 of 0.01 +/-0.004 at -80 mV were observed in the presence of I 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 P-0 (for all data records) at 10 muM was 0.030 +/-0.017 and 0.030 +/-0.028 at 1 mM.