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Effects of length changes on Na + current amplitude and excitability near and far from the end‐plate
Author(s) -
Ruff Robert L.
Publication year - 1996
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/(sici)1097-4598(199609)19:9<1084::aid-mus2>3.0.co;2-w
Subject(s) - membrane , sarcolemma , biophysics , membrane potential , chemistry , muscle fibre , neuromuscular junction , materials science , anatomy , skeletal muscle , biology , biochemistry , neuroscience
Abstract Na + current (I Na ), membrane capacitance (C m ), 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. I Na normalized to C m , 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 m and I Na did not change in response to changes in fiber length. On EJ membrane, I Na , C m , 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 fiber length. The higher density of Na + channels near the end‐plate increases the safety factor for neuromuscular transmission by lowering the AP threshold. © 1996 John Wiley & Sons, Inc.