Premium
Changes in threshold for calcium transients in frog skeletal muscle fibres owing to calcium depletion in the T‐tubules.
Author(s) -
Miledi R,
Parker I,
Zhu P H
Publication year - 1983
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1983.sp014936
Subject(s) - calcium , depolarization , biophysics , chemistry , barium , calcium in biology , membrane potential , contraction (grammar) , endocrinology , inorganic chemistry , biology , organic chemistry
Strength‐duration curves were measured for voltage‐clamp depolarizations required to elicit a just detectable rise in intracellular calcium, as monitored using arsenazo III, in frog twitch muscle fibres. In normal Ringer solution, the threshold for a 5 sec duration depolarization was about 5 mV more negative than for a 200 msec duration pulse. The shift in threshold comparing 200 msec and 5 sec pulses was almost abolished in bathing solutions including magnesium or nickel (4 mM), or where the free calcium concentration was buffered. The shift in threshold was little changed by substitution of barium for calcium. These results can be explained by supposing that the 5 sec depolarization activates an inward calcium flux across the T‐tubule membrane, which decreases the calcium concentration in the tubules, and hence alters the threshold for activation of excitation‐contraction (e.‐c.) coupling because of surface charge effects.