Excitation-Contraction Coupling in a Barnacle Muscle Fiber As Examined with Voltage Clamp Technique

Abstract

Relations between the membrane potential and the tension associated with changes in membrane potential were analyzed in barnacle giant muscle fibers by using voltage clamp techniques. With a step change in membrane potential the tension reaches its final level with a time course which is expressed by the difference of two exponential functions. The time constants rl (0.2-0.4 sec at 23°C) and r2 (0.07-0.12 sec at 23°C) are independent of the new membrane potential at least for a relatively small membrane potential change while the final level of tension is a function of the potential. Decreasing the temperature increases both rl and T2 (Q~0 = -2 to -3 ) and the increase of the tonicity of the external medium increases rx but not r2. The final level of tension is related by an S-shaped curve to the membrane potential. The slope of the final tension-meml~rane potential curve increases with increasing external Ca concentration and is reduced when a small amount of transition metal ions is added to the medium. This suggests that the influx of Ca ions through the membrane is an important factor in the development of tension.The relation between muscle tension and membrane potential has been studied in frog muscle fibers (Hodgkin and Horowicz, 1960), in cardiac muscle fibers (Niedergerke, 1956 b), and in muscle fibers of a barnacle, Balanus nubilus Darwin (Hoyle and Smyth, 1963) by observing potassium contractures. Similar studies have also been done by altering the membrane potential with polarizing currents in crayfish muscle fibers (Orkland, 1962 a) and in barnacle muscle fibers (Edwards, Chichibu, and Hagiwara, 1964). Considerable information has been accumulated from these studies on the relation between the amplitude of muscle tension and the membrane potential. However, very little has been done to analyze how the time course of tension development is determined by changes of the membrane potential.For this type of analysis it is necessary to control the membrane potential of I57

Calcium and potassium currents of the membrane of a barnacle muscle fibre in relation to the calcium spike

“…The slightly larger maximum value at the peak inward current found with procaine ( Fig. 4A) corresponds to the finding that the maximum rate of rise of the spike occasionally shows a slight increase after procaine (Hagiwara & Nakajima, 1966 b It has been reported that some transition metal ions such as Co2+ or Mn2+ suppress the spike potential of barnacle muscle fibres (Hagiwara & Nakajima, 1966b;Hagiwara & Takahashi, 1967). Figure 4B shows the current-voltage relations of the membrane of the same fibre treated with Ca-chelating agent examined before and after addition of 30 mM-CoCl2 in the normal Na-saline.…”

“…This shift is considered a result of the stabilizing action of Ca ions, seen under voltage clamp conditions as a shift of the currentvoltage relation along the potential axis (Hagiwara, 1966). If the Ca concentration is varied in the presence of a relatively large amount of Mg ions, for example 100 mM-MgCl2, the threshold membrane potential becomes independent of the Ca concentration at least in the range between 10 and 100 mm (Hagiwara & Takahashi, 1967). The three traces in the inserts of Fig.…”

Effect of pentachlorophenol on calcium accumulation in barnacle muscle cells.

“…Figure 1B depicts that 0-1 mM PCP promoted a more modest but still significant (*) increase in Ca2+ uptake which was about 4-fold greater than the controls at 40 min incubation. The delay observed (40-60 min) in reaching the maximum PCP-induced Ca2+ uptake may be due, at least in part, to the fact that barnacle muscle cells possess deep branched invaginations (Hoyle, McNeill & Selverston, 1973) (Hagiwara, Takahashi & Junge, 1968;Ashley & Ridgway, 1970;Atwater, Rojas & Vergara, 1974). Similarly, barnacle muscle cells possess a Na+-Ca2+ exchanger which can rapidly mediate Ca2+ influx in exchange for intracellular Nae (Rasgado-Flores & Blaustein, 1987;Rasgado-Flores et al 1989).…”

The effect of quinine on tension development, membrane potentials and excitation‐contraction coupling of crab skeletal muscle fibres

“…Although the triggering of the EC coupling events in some crustacean skeletal muscles does not appear to be dependent upon the attainment of a distinct mechanical threshold (Reuben, Brandt, Garcia & Grundfest, 1967), a distinct threshold exists in crab fibres (Huddart, 1969a), as is the case in vertebrate (Hodgkin & Horowicz, 1960) and many other arthropod skeletal muscles (Atwood, 1962;Edwards, Chichibu & Hagiwara, 1964;Hoyle, 1961;Hoyle & Smyth, 1963;Hagiwara, Takahashi & Junge, 1968;Huddart & Abram, 1969). Whereas caffeine significantly lowers the mechanical threshold of crab skeletal-muscle fibres (Huddart, 1969a), there is no evidence from this study that quinine has such an effect on crab muscle, although a lowering of mechanical threshold by quinine has 652 H. HUDDART QUININE AND CRAB SKELETAL MUSCLE been reported in frog skeletal muscle (Sandow et al 1964).…”