Calcium movements in single crustacean muscle fibres

SUMMARY1. Single smooth muscle cells were prepared from the guinea-pig taenia coli and the porcine coronary artery by treatment with collagenase, in order to measure the 45Ca flux with special reference to the effects of external cations.2. In excess [K]o solution, cell suspensions prepared from both tissues showed an increased 45Ca uptake within 3-5 min. In Na-free solution, the cells prepared from taenia coli, but not from coronary artery showed an increased 45Ca uptake. The Ca uptake of the cells paralleled with the tension increase recorded from tissues of both species.3. The efflux of 45Ca into Ca-free EGTA containing solution was markedly increased by [Na] 7. In cells from the taenia coli, 45Ca efflux could still be observed in nominally Naand Ca-free solution. This residual 45Ca efflux made a large contribution to the total 45Ca efflux.8. When 45Ca uptake was measured in Na-free (Tris) solution, the [Na]o-activated, [Ca]o-activated and residual 45Ca effluxes of cells from the taenia coli were accelerated, non-selectively.9. These results obtained with cells prepared from the guinea-pig taenia coli are comparable to the Ca2+ efflux mechanism seen in the squid axon. However, maintenance of low concentrations of [Ca]i seems to require not only the above three 45Ca efflux mechanisms, but also Ca sequestering mechanisms in the cell.0022-3751/81/3240-0912 $07.50

Section: -2 Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of external cations on calcium efflux from single cells of the guinea‐pig taenia coli and porcine coronary artery.

Hirata¹,

Itoh²,

Kuriyama³

1981

“…Some of the evidence favours the view that the fall of aya in low Nao was because of a Na efflux in exchange for either Ca or Mg, a system similar to that found in other crustacean muscles (Baker, 1972;Ashley & Ellory, 1972;Ashley, Ellory & Hainut, 1974). Firstly, changes of aj a were very sensitive to the size of the Na gradient across the membrane; secondly, the effect was inhibited by the elements Co, Mn and La in concentrations which have been found to inhibit Na/Ca exchange in squid giant axon (see Baker, 1972) and thirdly, there was always very little change in membrane potential during such large changes of ai a suggesting that the Na/Ca (or Mg) exchange might be electroneutral.…”

Section: Effect Of Changes In the External Phmentioning

confidence: 99%

“…It was found however after long exposure to either drug that large contractures occurred whenever Na0 was reduced for more than 2-3 min. Ashley & Ellory (1972) and Ashley, Ellory & Hainut (1974) have reported that D600 has no effect on the …”

Section: Effects Of D600 and Verapamitmentioning

confidence: 99%

The effect of lowering external sodium on the intracellular sodium activity of crab muscle fibres.

Vaughan‐Jones¹

1977

SUMMARY1. Intracellular Na activity, aNa, was continuously measured in crab (Carcinus maenas) muscle fibres using a recessed-tip Na+-sensitive glass micro-electrode. Experiments could last up to several hours. a~a remained stable during prolonged experiments. The mean resting a0a was 8*4 + 0.02 mM (S.E. of mean for eighty-nine fibres) and the mean resting membrane potential was 65*3 mV + 0 3 (S.E. of mean for eighty-nine fibres).2. Reducing [Na]0 to I normal (maintaining ionic strength with equivalent amounts of either Li or Tris) caused a large and rapid fall of aZa. There appeared to be two components of the effect, a fast and slow. The initial fast rate of decrease was about 3-5 m-mole/min decreasing to half this value in about 1 min. The rate of decrease of aya was not linearly related to aNa. The size of the fast change of aya was related to

“…In some experiments the trivalent ion La was included in the external solution. This agent is known to reduce membrane Ca transport in these fibres (Ashley, Ellory & Hainaut, 1974) and thus should prevent a significant depletion of the more slowly equilibrating compartments (see Mayer, Van Breemen & Casteels, 1972). The fibre responsiveness to injected caffeine after exposure to the experimental salines was then re-assessed.…”

Section: Introductionmentioning

confidence: 99%

Caffeine and the contractility of single muscle fibres from the barnacle Balanus nubilus

Ashley

Ellory

Griffiths

1977

Self Cite

SUMMARY1. In single striated muscle fibres from the barnacle Balanus nubilu8 tension development following axial injection of caffeine (50 mM in 150 mM-KCl, pH 7.1) was used as an index of releasable Ca. It was shown that fibres incubated in 0 Ca (Na replaced) salines for up to 400 min gave ca. 15 % of the control tension response. Inclusion of 1 mM-La in the 0 Ca (Na) saline significantly reversed this decline.2. Estimates of the total fibre calcium assayed under the same experimental conditions indicated a 67 % loss of fibre Ca in 0 Ca, and only a 37 % loss in La-0 Ca media. No correction was made for the loss of calcium from the extracellular space.3. Experiments with 45Ca indicated that the efflux of calcium from this preparation was inhibited by 1 mM-La externally and that this effect was still significant even in the presence of 0 Ca (Na) salines. The caffeinestimulated efflux of Ca was also reduced by ca. 70 % in the presence of 1 mm La saline externally.4. The influx and efflux of 14C caffeine were shown to be rapid, and apparently passive. The diffusion coefficient for caffeine following intracellular injection was 2-4 + 0-2 x 10-6 cm2 sec-' at 18-22°C.5. There was no significant loss of 140La over a period of 2 hr following axial micro-injection into the fibres.6. In 140La uptake experiments there was a progressive increase in the La space over 10-5 hr, in contrast to the results with [3H]inulin, whose uptake saturated in ca. 1-5 hr. The probability of surface binding and the precipitation of La salts in the extensive extracellular space was suggested as an explanation.7. It is concluded that internal Ca within the sarcoplasmic reticulum, and not cleft or extracellular Ca is the most significant source for these caffeine-induced contractions. Fluxes across the surface membrane can however alter the internal Ca stores over longer periods of time.