Effects of External Calcium Deprivation on Single Muscle Fibers

Abstract

Deprivation of external calcium causes sudden potentiation of the twitch response of single muscle fibers. The potentiation was 64 4-8 %. Potentiation is simultaneous with membrane depolarization occurring after Ca +÷ removal. This depolarization amounted to 9 4-2 my. Ca ++ removal also alters the action potential. 3 rain after calcium withdrawal, action potential amplitude fell by 36 4-3 my; maximum rates of rise and fall of the spike decreased by 55 4-5 and 63 4-5 % respectively. Changes in shape of the A. P. differ from those seen with other potentiators of the twitch response, such as Zn ++. After short exposure to calcium-free media, potassium-induced contractures show potentiation of peak tension. The S-shaped curve relating potassium contracture tension to log [K]o shifts to the left after such treatment. Calcium deprivation also increased the rate of relaxation of the contractures. This effect depends on the duration of calcium deprivation, and is probably related to the effect of calcium lack on the membrane. The change in relaxation occurred immediately after calcium deprivation, and was reversed by sudden readmission of calcium. Relaxation of twitch and tetanus responses also were affected by Ca lack, but not as rapidly as potassium contractures. The results suggest that external calcium is not directly involved in the process responsible for tension development, supporting the view that this process is mediated by translocation of intracellular calcium. The relaxation process, however, appears to be rapidly affected by deprivation of external calcium.Normally the contractile response of muscle fibers is triggered by the lowering of the fiber m e m b r a n e potential to a threshold value at which the excitationcontraction coupling (ECC) process begins to be effective (1--4). T h e hypothesis which postulated t h a t calcium ions entering the fibers from the extracellular space upon depolarization of the m e m b r a n e activated the contractile material (5, 6) appears to be inadequate on the basis of theoretically calculated diffusion delays (4,7,8). However, the presence in the interior of the fiber of the system of transverse tubules which open out directly into the external space could reduce such delays (9, 10).

Effects of external calcium reduction on biphasic potassium contractures and action of divalent cations on the calcium reduction in frog single twitch muscle fibers.

“…On the other hand, the peak tension of the secondary component was rapidly inhibited by the Ca2+ reduction, in contrast to the potentiation of the peak tension of the initial component. The result that shows the initial component of the contractures being potentiated at the initial stage of the Ca2+ reduction is in agreement with that of CAPUTO and GIMENEZ (1967), who reported that twitch tension and K contracture tension were strongly enhanced within 2 min when single muscle Japanese Journal of Physiology fibers were exposed to low Ca2+ solutions. In addition, the result that shows the peak tension of the initial component being inhibited at 20 min after Ca2+ reduction is comparable with those of FRANK (1960) and KOSAKA et al (1977).…”

“…In addition, the result that shows the peak tension of the initial component being inhibited at 20 min after Ca2+ reduction is comparable with those of FRANK (1960) and KOSAKA et al (1977). CAPUTO and GIMENEZ (1967) noticed the potentiating effect as the short term effect of the Ca2+ reduction. With respect to this, the inhibitory effect of Ca2+ reduction previously reported by FRANK (1960) and by KOSAKA et al (1977) and the effect observed in the present paper may be regarded as the long term effect of Ca2+ reduction.…”

Membrane potential, contractile activation and relaxation rates in voltage clamped short muscle fibres of the frog.

“…These experiments were carried out following the procedure of Hodgkin & Horowicz (1960). prolonged contractile responses represent the time necessary for the activator concentration in the myoplasm to be reduced from a supramaximal to a maximal concentration. Suggestive but not conclusive evidence against the idea that the spontaneous relaxation of potassium contractures was due to exhaustion of a store of activator available for release was obtained by changing differently the time course 187 C. CAPUTO AND P. F. DE BOLANOS of these responses by several experimental procedures (Caputo & Gimenez, 1967;Caputo, 1976).…”

Enhanced Excitation-Coupled Calcium Entry in Myotubes Expressing Malignant Hyperthermia Mutation R163C Is Attenuated by Dantrolene

“…Moreover, evidence for the role of ECCE in normal use-dependent physiology and pathophysiology of adult skeletal muscles may have been described in earlier studies but were underappreciated. For example, the rate of relaxation of contractures after prolonged applications of extracellular K ϩ was faster in the absence of extracellular Ca 2ϩ than in its presence (Caputo and Gimenez, 1967), whereas brief depolarization in Ca 2ϩ -free solutions was not different from the response in Ca 2ϩ -replete external medium (Caputo and Gimenez, 1967;Grabowski et al, 1972). More recently, age-related denervation of fast skeletal muscle was found in senescent mice, and muscle fibers isolated from them were found to show dependence on extracellular Ca 2ϩ to maintain tetanic force (Payne et al, 2007).…”