Excitation of skinned muscle fibers by imposed ion gradients. II. Influence of quercetin and ATP removal on the Ca2+-insensitive component of stimulated 45Ca efflux.

Abstract

Ionic gradients imposed by choline Cl replacement of K methanesulfonate (Mes) at constant [K][Cl] product stimulate "Ca efflux from skinned muscle fibers ; a small, sustained Ca"-insensitive efflux component, observed in EGTA, appears to grade a much larger Ca"-dependent component responsible for contractile activation and is likely to reflect intermediate steps in excitation-contraction coupling. The present studies examined ATP-related effects on the Ca"-insensitive stimulation . "Ca efflux was measured on segments of frog semitendinosus muscle skinned by microdissection, with isometric force monitored continuously . The Ca"-insensitive component was potentiated by quercetin, a flavonoid thought to inhibit the sarcoplasmic reticulum (SR) Ca pump by stabilizing a phosphorylated intermediate . Quercetin increased the stimulated net "Ca release in the absence of EGTA, as expected from inhibition of reaccumulation, but its effectiveness in EGTA indicated potentiation of unidirectional efflux as such . Quercetin also increased unstimulated (control) "Ca efflux in EGTA, to a smaller extent ; potentiation appeared to be a function of efflux, with stimulation above control loss increased -2 .6-fold . ATP removal before stimulation, which led to rigor force and increased stiffness, prevented all quercetin effects in EGTA . ATP removal by itselfinhibited ionic stimulation of the Ca"-insensitive component, with little residual increase above the parallel control loss. Addition of the nonhydrolyzable ATP analogue AMP-PCP ([adenylyl-/3,-y-methylene]diphosphate) (0 .8 mM) after ATP removal gave similar results to ATP-free solution, which suggests that adenine nucleotide binding alone does not support stimulation by choline Cl . These results imply a fundamental role for ATP in the excitation of skinned fibers by imposed diffusion potentials; they also suggest that ATP regulates the SR Ca efflux channel, in a manner that could provide the positive feedback in Ca"-dependent Ca release.J. GEN. PHVstot. .

Effect of Mg2+ on the control of Ca2+ release in skeletal muscle fibres of the toad.

“…Adenine nucleotides have been shown to potentiate the action of Ca2+ in opening the release channels in skinned fibre preparations (Endo, 1985), isolated SR vesicles ) and lipid bilayer experiments (Smith et al 1986). In the absence of ATP, raising [Ca2+] only causes a relatively small increase in the rate of Ca2+ release from SR vesicles ) and depolarization cannot elicit Ca2+ 17-2 515 G. D. LAMB AND D. G. STEPHENSON release in skinned muscle fibres (Stephenson, 1985). The following experiments show that the massive release of Ca2+ in low [Mg2+] reported above does not occur in the absence of ATP.…”

“…In the absence of ATP, raising [Ca2+] only causes a relatively small increase in the rate of Ca2+ release from SR vesicles (Stephenson, 1985 of maximum tension (e.g. Fig.…”

The effect of the aluminum chloride – quercetin complex on Ca(2+),Mg(2+)-ATPase activity and contraction dynamic properties of muscle tibialis anterior from Rana temporaria

“…Flavonoids are known to affect contractile systems of various biological objects. They have been demonstrated to regulate activity of all types of muscles, including smooth, skeletal, and cardiac muscle [2,3]. It has been shown that quercetin acts as a competitive inhibitor in ATP binding to an enzyme.…”

“…Moreover, chelate complexes of flavonoids and metals act as free radical scavengers and detoxicants [7,8]. Aluminum-flavonoid complexes may be produced during cooking of vegetable food in an aluminum vessel and consequently consumed [3]. It has been shown [6], that flavonoid interaction with metal ions, e.g.…”

“…Changes in ATPases activity under aluminum and quercetin effect may be an important factor in cellular dysfunction caused by disruption of transmembrane cation transport [3]. Thus, Ca 2+ ,Mg 2+ -ATPase activity decrease probably results from compromised structural integrity of membranes of SR and not from direct effect of flavonoids and their metallic complexes upon the enzyme [10].…”