Calcium and potassium currents in muscle fibres of an insect (Carausius morosus).

Abstract

SUMMARY1. A three electrode voltage-clamp was used to investigate membrane currents in the skeletal muscle fibres of the stick insect, Carausius morosus. Contraction was blocked by hypertonic solutions.2. Membrane currents elicited by step depolarizations consisted of an inward current, an early outward current and a delayed outward current.3. The reversal potential of the delayed outward current did not change when S042-was substituted for Cl-, but shifted by 14-1 mV when [K]o was increased from 20 mM to 40 mm in S042-solution, suggesting that the delayed current is carried by K+. Both early and delayed outward currents were substantially reduced by 120 mMtetraethylammonium (TEA) ions. 4. The small size of the shift in the reversal potential ofthe delayed outward current with increased pulse duration suggests that the delayed current measured flows mainly across the surface membrane.5. Increasing [Ca]o made the apparent reversal potential for the inward current (120 mM-TEA Ringer) more positive and increased the size of the maximum inward current. However, Ca-currents showed saturation with increasing [Ca]0, indicating that there is a site to which Ca ions bind during their passage through the membrane. The dissociation constant of this site was 7-3 mm at 0 mV and was voltage-dependent.

Voltage clamp analysis of membrane currents in larval muscle fibers of Drosophila: alteration of potassium currents in Shaker mutants

“…Analysis of Drosophila larval muscles has revealed several physiologically distinct membrane currents similar to those found in other insect muscles (Yamamoto and Washio, 1981;Yamamoto et al, 1981;Ashcroft and Stanfield, 1982). Voltage-dependent Ca2+ channels are responsible for the inward current but Na+ channels are not detectable in the larval muscles, consistent with a previous current clamp study (Suzuki and Kano, 1977).…”

“…In Drosophila larval muscles, IK inactivates slowly, resembling the observations reported in a number of different tissues including frog skeletal muscles (Adrian et al, 1970) and adult stick insect muscles (Ashcroft and Stanfield, 1982). Depletion of intracellular K+ or accumulation of external K+ in the vicinity of the membrane surface may also lead to decline of /k.…”

“…Drosophila larval muscles, like those of other arthropods (Fatt and Ginsborg, 1958;Werman et al, 1961;Yamamoto et al, 1981;Ashcroft and Stanfield, 1982), have voltage-dependent Ca*' channels but do not have Na+ channels. There are at least two outward K+ currents: a rapid inactivating transient, similar to In described in molluscan neurons (Connor and Stevens, 1971 b), and a delayed, sustained outward current, similar to the delayed rectifier, IK (Hodgkin and Huxley, 1952c).…”

Arsenazo III transients and calcium current in a normally non‐spiking neuronal soma of crayfish.

“…However, a two-time-constant recovery from inactivation was not strongly supported because (1) the correlation coefficient for the fast phase (-0-81) is lower and (2) the related time constant (0-24 s) is very close to the test-pulse duration. These results can be compared with those obtained for Ca2+ current by other authors who concluded that two time constants existed using a similar two-pulse protocol: 0 42/4A4 s (Tillotson & Horn, 1978); _0,1/ _1 s (Adams & Gage, 1979); 0 12/9 4 s (Plant & Standen, 1981); 0-06/0 89 s (Ashcroft & Stanfield, 1982).…”

“…Inactivation of Ca2+ entry It has been suggested in a number of preparations (Hagiwara & Nakajima, 1966;Tillotson, 1979;Ashcroft & Stanfield, 1982;Standen & Stanfield, 1982;Eckert & Ewald, 1983) that the intracellular free Ca2+ controls the inactivation of the Ca2+ channel. However, in most experiments the precise evaluation of Ca2+ current is difficult since it is usually contaminated by the outward current which is very difficult to eliminate.…”