Inositol 1,4,5-trisphosphate receptors (IP(3)R) are ubiquitous intracellular Ca(2+) channels. They are regulated by IP(3) and Ca(2+) and can thereby both initiate local Ca(2+) release events and regeneratively propagate Ca(2+) signals evoked by receptors that stimulate IP(3) formation. Local signaling by small numbers of IP(3)R underpins the utility of IP(3)-evoked Ca(2+) signals as a ubiquitous signaling pathway. The physiological impact of Ca(2+) release by very small numbers of IP(3)R underscores the necessity to understand the behavior of IP(3)R at the single-channel level. In addition, and in common with analyses of every other ion channel, single-channel analyses have the potential to define the steps linking IP(3) binding to channel opening. Patch-clamp recording, by resolving the openings and closings of single channels with exquisite temporal resolution, is the most powerful technique for analysis of single-channel events. It has contributed enormously to the understanding of gating and desensitization/inactivation of numerous ion channels. However, most IP(3)R reside within intracellular membranes, where they are inaccessible to conventional patch-clamp recording methods. Here, we describe the application of nuclear patch-clamp methods to single-channel analyses of native and recombinant IP(3)R.
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