Effects of length changes on Na+ current amplitude and excitability near and far from the end-plate

✍ Scribed by Robert L. Ruff

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 874 KB
• Volume: 19
• Category: Article
• ISSN: 0148-639X
• DOI: 10.1002/(sici)1097-4598(199609)19:9<1084::aid-mus2>3.0.co;2-w

✦ Synopsis

Na+ current ( lNa), membrane capacitance (C,), action potential (AP) properties, and cable properties were studied on the end-plate (E), the end-plate border (EB), and extrajunctional (EJ) membrane of rat fast twitch muscle fibers. INa normalized to C, , which is proportional to the density of Na' channels, was the same on the E and the EB and smallest on EJ membrane. The AP threshold was lower and rate of rise of the AP was larger at the EB compared with EJ membrane. On the E and the EB, C, and INa did not change in response to changes in fiber length. On EJ membrane, lNa, C, , and membrane cable properties changed in a manner consistent with folding and unfolding of the sarcolemma during length changes. The stiffness of the E membrane may add mechanical stability to the neuromuscular junction so that the electrical properties of the end-plate do not change with 'iber length. The higher density of Na+ channels near the end-plate increases the safety factor for neuromuscular transmission by lowering the AP threshold.