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

SUMMARY1. In the first part of this investigation we studied the experimental conditions under which the 'lanthanum method' gives valid estimations of the changes in intracellular calcium induced by either tetraethylammonium chloride (TEA) or high K in the rabbit main pulmonary artery. Subsequently, the effect of TEA on Ca movements in this blood vessel was measured.2. The uptake of 140La by the vascular tissue is time-and concentration-dependent;it is separated into an early and a late phase. La binds to at least two classes of extracellular sites with affinities of 0-06 and 4-76 M. 3. A 1 hr exposure of the vascular strips to a 1 mM-La solution appears to be a convenient treatment for removal of Ca from the extracellular space. Under these conditions (a) 45Ca efflux from an intracellular compartment loaded with Ca during exposure to TEA or K is virtually blocked, (b) there is no major penetration of La into the smooth muscle cells as revealed by electron microscopy, and (c) there is no change in the size of the extracellular space.4. TEA increases *in a concentration-dependent manner the La-resistant 45Ca content (maximum increase 0-18 m-mole 45Ca/kg wet weight in response to 70 mM-TEA). There is a linear relationship between log concentration TEA and 45Ca influx. 5. The calcium antagonist verapamil (10-6 and 10-5 M) inhibits the TEA-induced 45Ca influx.

Section: Discussionsupporting

confidence: 59%

Section: Discussionsupporting

confidence: 53%

The effect of tetraethylammonium chloride on calcium fluxes in smooth muscle from rabbit main pulmonary artery.

Haeusler¹,

Kühn²,

Thorens³

1980

“…Under the assumption that the rate-limiting step of this tension development is the rate of caffeine diffusion, this result suggests that the apparent diffusion coefficient of caffeine in cardiac muscle is 15 +0-5 x 10-6cm2/s (mean+s.D., n = 8) (see Kitazawa, 1984). This value is similar to that measured directly using [14C]caffeine in barnacle muscle fibres (Ashley, Ellory & Griffiths, 1977). On the basis of the estimated concentration profile derived from the diffusion equation (see Fig.…”

supporting

confidence: 77%

Caffeine contracture in guinea‐pig ventricular muscle and the effect of extracellular sodium ions.

Kitazawa

1988

SUMMARY1. The mechanisms underlying the virtual absence of caffeine contracture in guinea-pig heart in a Na+-rich external solution were reinvestigated in small (50-120 ,tm thick) bundles of intact and skinned papillary muscle fibres.2. In Na+-free solution, the peak tension of 30 mM-caffeine contracture corresponded to the maximum tension of the skinned fibres, and was independent of changes in [Ca2+] 3. In the absence of Ca2+, replacement of Na+ with K+ allowed caffeine to evoke a large contracture, showing that there was sufficient calcium stored in the cells under Na+-rich conditions. After treatment with 30 mM-caffeine in the Na+-rich, Ca2+-free solution, and upon replacement of all Na+ with Li+, caffeine was still able to produce a large contracture, which was dependent upon Ca2+ pre-loading of the cells before the first caffeine treatment and upon the subsequent duration in the Na+-free solution.4. Replacement of Li+ with Na+ during the contracture led to rapid relaxation which was delayed by an increase in [Ca2+]0, depolarization by K+, and addition of La3+ and Mn2+. After Na+-induced complete relaxation in the absence of Ca2+, upon removal of the drugs and Na+, subsequent application of caffeine to the cells evoked a large contracture without Ca2+ reloading. 5. In the skinned fibres, 30 mM-caffeine increased the Ca2+ sensitivity of the contractile system and depressed the maximum tension. An increase in Na+ from 8f4 to 58-4 mm altered neither Ca2+ sensitivity nor the rate of tension development in the absence or presence of caffeine.6. Increase in Na+ affected neither the rate nor the amount of Ca2+ uptake by the sarcoplasmic reticulum (SR) in the absence or presence of caffeine. Increasing Na+ slightly inhibited the caffeine-induced Ca2+ release from the SR, but more than 10 mM-caffeine produced SR Ca2+ depletion.7. In the presence of a strong Ca2+ buffer, the steady level of Ca2+ uptake by the SR with 1 mM-caffeine was equal to the amount of Ca2+ remaining in the SR just after the application of caffeine, indicating that Ca2+ release was not inactivated.8. The

“…In agreement with this, a very slow, partial recovery of pHi was often observed during a prolonged wash-off of CCCP. Absence of an effect of caffeine on CCCP-induced contracture Caffeine has been shown to release calcium from the sarcoplasmic reticulum (SR) of crustacean muscle fibres, both intact and skinned (Chiarandini, Reuben, Girardier, Katz & Grundfest, 1970;Ashley, Ellory & Griffiths, 1977). Evidence has been presented that protonophores, including CCCP, are also capable of releasing calcium from the SR (Shoshan, MacLennan & Wood, 1981).…”

Section: Effects Of Cccp On Resting Tension and Membrane Potentialmentioning

confidence: 99%

Fall in intracellular pH and increase in resting tension induced by a mitochondrial uncoupling agent in crayfish muscle.

Kaila

Mattsson

Voipio

1989

SUMMARY1. The influence of the mitochondrial uncoupling agent carbonylcyanide-mchlorophenylhydrazone (CCCP) upon resting tension and intracellular pH (pH1) was studied in the dactyl opener muscle of the crayfish. pH, was measured with liquid sensor H+-selective microelectrodes.2. CCCP (10-6-10-5 mol 1-) induced a reversible, tonic contracture which was associated with a depolarization of the membrane potential. Both effects were augmented by a fall and inhibited by a rise in extracellular pH. The action of CCCP on tension was not mimicked by cyanide+oligomycin or by cyanide+dicyclo-hexylcarbodiimide nor was it inhibited by pre-exposure to these agents.3. CCCP produced an initial alkalosis of less than 0.1 units and thereafter a fall in pHi of 044-0-6 units during which the sarcolemmal H+ driving force decreased from 61 to 15 mV. The apparent influx of H+ due to CCCP had a maximum of 2X7 mequiv 1-1 min-'. The CCCP-induced acidosis was unaffected by iodacetate (0-5 mmol I-') but it was inhibited by a depolarization of the membrane potential.4. The contraction caused by CCCP was not due to the simultaneous fall in pH, since an intracellular acidosis of equal magnitude, produced by propionate (50 mmol l-l), did not lead to force generation. In addition, propionate had an inhibitory effect on the depolarization and contracture caused by CCCP. 5. Both the depolarization and the contracture caused by CCCP were inhibited by y-aminobutyric acid (GABA). The contracture was blocked by Cd2 , Mn2+ and by a nominally Ca2+-free medium but not by a pre-exposure to caffeine (20 mmol 1-1).Cd2+ and Mn2+ had no influence on the fall of pHi caused by CCCP.6. It is concluded that CCCP induces a sarcolemmal H+ conductance which leads to a fall in pHi and to a depolarization of the membrane potential. This depolarization activates sarcolemmal, voltage-dependent calcium channels and thereby induces an increase in tension. The initial alkalosis produced by CCCP may be due to a transient uptake of H+ by mitochondria.