Identification and localization of Ca(2+)-activated K+ channels in rat sciatic nerve.

To understand the physiology of Schwann cells and myelinated nerve, we have been engaged in identifying K+ channels in sciatic nerve and determining their subcellular localization. In the present study, we examined the slo family of Ca(2+)-activated K+ channels, a class of channel that had not previously been identified in myelinated nerve. We have determined that these channels are indeed expressed in peripheral nerve, and have cloned rat homologues of slo that are more than 95% identical to the murine slo. We found that sciatic nerve RNA contained numerous alternatively spliced variants of the slo homologue, as has been seen in other tissues. We raised a polyclonal antibody against a peptide from the carboxyl terminal of the channels. Immunocytochemistry revealed that the channel proteins are in Schwann cells and are associated with canaliculi that run along the outer surface of the cells. They are also relatively concentrated near the node of Ranvier in the Schwann cell outer membrane. This staining pattern is quite similar to what we previously reported for the voltage-dependent K+ channel Kv 1.5. We did not observe staining of axons or connective tissue in the nerve and so it seems likely that most or all of the splicing variants are located in the Schwann cells. The localization of these channels also suggests that they may participate in maintaining the resting potential of the Schwann cells during K+ buffering.