Frog tonic muscle fibers: extracellular calcium and excitation-contraction coupling.
Frog tonic muscle fibers: extracellular calcium and excitation-contraction coupling.
复制标题
青蛙的强直肌纤维：细胞外钙和兴奋-收缩耦合。
DOI：
10.1152/ajplegacy.1970.219.5.1446
复制
发表时间：
1970
期刊：
影响因子：
--
通讯作者：
A. C. Kirby
中科院分区：
文献类型：
--
作者：
A. C. Kirby
METHODSSmall bundles (lo-25 fibers) of tonic fibers were isolated from the iliofibularis muscle of Rana@ iens according to the method of Liittgau(7). The tonic fibers form a fairly homogenous bundle where the nerve enters the iliofibularis muscle. The major portion of the muscle opposite the nerve entry was snipped away until approximately 50 fibers remained. Then a drop of 50 mM potassium solution was dripped onto the muscle. Under these conditions the tonic and phasic fibers can be differentiated visually, because the phasic fibers soon visibly relax while the tonic fibers remain contracted as long as they are immersed in the high-potassium solution. The phasic fibers were then cut away, and the tonic fiber bundle was stored in cold Ringer until used. The experiments were performed between July and October and were done at room temperature, 20-25 C.Solutions. The normal Ringer solution contained(mM): NaCI, 117.4; KCL, 2.5; CaCl, 2.0; and Tris buffer, 2.0. The pH was 7.1-7.3 in all solutions. The solutions were vigorously bubbled with 100% oxygen for 10 min before each experiment. In order to prevent changes in internal ion concentrations while the contraction-inducing solutions (described below) were being used, the product ([K+ 10+ b [Na+].) X [Cl-],, where b= PNa/Pk, was kept constant (4). This was accomplished by replacing Cl-with the appropriate amount of methyl sulfate. In order to eliminate the possibility that significant concentrations of sulfate might build up, the solutions were freshly made and the pH was checked before and after each experiment. This modification of the standard procedure of keeping [Kf],, X [Cl-]. constant was necessary, because P&Pk was found to be appreciable(0.13)(4) q Five different [K+ 10 values were employed in the contraction-inducing solutions-10, 15, 20, 30, and 50 mM. In all five of these solutions K0+ Na,= 119.9 mM. In the experiments on Na+-Ca+ f antagonism some of the sodium was replaced by an equivalent amount of sucrose. Three [Ca++]. values were used: 0.4, 2.0, and 10.0 mM. The calcium concentration was altered in both bathing Ringer solution and in the various contraction-inducing solutions so that a total of nine different combinations of [Ca* &, in bathing and contracting solutions could be presented to each muscle bundle at a given [K+ lO. For example, a bundle could be bathed in 0.4 mM: calcium-Ringer and then contracted in either 0.4, 2.0, or 10.0 mM calcium. Relative tension is the ratio of the tension produced under the experimental conditions to that produced by the
