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

Abstract.

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 (P _o) 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 _o 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 _o 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 P _o (for all data records) at 10 µM was 0.030±0.017 and 0.030±0.028 at 1 mM.