Expression of IP3 receptor isoforms at the nodes of Ranvier in rat sciatic nerve.

Inositol 1,4,5-trisphosphate receptors (IP3R) are modulated by the second messenger IP3, which induces intracellular calcium release. Using immunohistochemical techniques, we show that the three isoforms are expressed in sciatic nerve. IP3R1 and IP3R2 are mainly present in the nucleus of Schwann cells. IP3R1 is also expressed in Schmidt-Lanterman incisures. IP3R3 is primarily localized at very high levels in nonmyelinating Schwann cells. Interestingly, the three isoforms are expressed at the nodes of Ranvier. IP3R1 is clustered at the node of Ranvier, in a distribution that is similar to the Nav1.6 sodium channels in the sciatic nerve. IP3R3 is present in the paranodal regions of the nodes. IP3R2 is concentrated in the vicinity of the node, and the outer Schwann cell cytoplasm similar to the Kv1.5 potassium channel.