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ATP-dependent interaction of propranolol and local anaesthetic with sarcoplasmic reticulum. Stimulation of Ca2+ efflux.

ABSTRACT: Preincubation of sarcoplasmic reticulum (SR) with propranolol or tetracaine inhibits Ca2+ accumulation and stimulates ATPase activity by more than 2-fold. This effect is obtained only when the preincubation is carried out in the presence of ATP or other nucleoside triphosphates. The (ATP + drug)-induced inhibition of Ca2+ accumulation is pH-dependent, increasing as the pH rises above 7.5. The presence of micromolar concentrations of Ca2+ or Mg2+ during the preincubation prevents the inhibitory effect of ATP plus drug on Ca2+ accumulation or ATPase activity. The (ATP + drug) modification of SR vesicles resulted in stimulation of a rapid Ca2+ efflux from passively loaded vesicles. The ATP-dependent inhibition of Ca2+ accumulation by the drug is obtained with other local anaesthetics. The drug concentration required for 50% inhibition was 0.15 mM for dibucaine and 0.4 mM for both propranolol and tetracaine, whereas it was 5 mM, 8 mM and greater than 10 mM for lidocaine, benzocaine and procaine respectively. The heavy SR vesicles were only slightly affected by the incubation with propranolol or tetracaine in the presence of ATP, but their sensitivity increased markedly after storage at 0 degrees C for 24-48 h. These results suggest that propranolol and some local anaesthetics, in the presence of ATP, stimulate Ca2+ efflux by modifying a protein factor(s) rather than the phospholipid bilayer.

SUBMITTER: Shoshan-Barmatz V

PROVIDER: S-EPMC1135477 | biostudies-other | 1988 Dec

REPOSITORIES: biostudies-other

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Stimulation of Ca2+ efflux from sarcoplasmic reticulum by preincubation with ATP and inorganic phosphate.

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Elongation and Contraction of Scallop Sarcoplasmic Reticulum (SR): ATP Stabilizes Ca2+-ATPase Crystalline Array Elongation of SR Vesicles.

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Interactions of phosphate groups of ATP and Aspartyl phosphate with the sarcoplasmic reticulum Ca2+-ATPase: an FTIR study.

Project description:Phosphate binding to the sarcoplasmic reticulum Ca2+-ATPase was studied by time-resolved Fourier transform infrared spectroscopy with ATP and isotopically labeled ATP ([beta-18O2, betagamma-18O]ATP and [gamma-18O3]ATP). Isotopic substitution identified several bands that can be assigned to phosphate groups of bound ATP: bands at 1260, 1207, 1145, 1110, and 1085 cm(-1) are affected by labeling of the beta-phosphate, bands likely near 1154, and 1098-1089 cm(-1) are affected by gamma-phosphate labeling. The findings indicate that the strength of interactions of beta- and gamma- phosphate with the protein are similar to those in aqueous solution. Two bands, at 1175 and 1113 cm(-1), were identified for the phosphate group of the ADP-sensitive phosphoenzyme Ca2E1P. They indicate terminal and bridging P-O bond strengths that are intermediate between those of ADP-insensitive phosphoenzyme E2P and the model compound acetyl phosphate in water. The bridging bond of Ca2E1P is weaker than for acetyl phosphate, which will facilitate phosphate transfer to ADP, but is stronger than for E2P, which will make the Ca2E1P phosphate less susceptible to attack by water.

| S-EPMC1366999 | biostudies-literature

Sarcoplasmic reticulum Ca2+ pumping kinetics regulates timing of local Ca2+ releases and spontaneous beating rate of rabbit sinoatrial node pacemaker cells.

Project description:RationaleSinoatrial node cells (SANCs) generate local, subsarcolemmal Ca(2+) releases (LCRs) from sarcoplasmic reticulum (SR) during late diastolic depolarization. LCRs activate an inward Na(+)-Ca(2+) exchange current (I(NCX)), which accelerates diastolic depolarization rate, prompting the next action potential (AP). The LCR period, ie, a delay between AP-induced Ca(2+) transient and LCR appearance, defines the time of late diastolic depolarization I(NCX) activation. Mechanisms that control the LCR period, however, are still unidentified.ObjectiveTo determine dependence of the LCR period on SR Ca(2+) refilling kinetics and establish links between regulation of SR Ca(2+) replenishment, LCR period, and spontaneous cycle length.Methods and resultsSpontaneous APs and SR luminal or cytosolic Ca(2+) were recorded using perforated patch and confocal microscopy, respectively. Time to 90% replenishment of SR Ca(2+) following AP-induced Ca(2+) transient was highly correlated with the time to 90% decay of cytosolic Ca(2+) transient (T-90(C)). Local SR Ca(2+) depletions mirror their cytosolic counterparts, LCRs, and occur following SR Ca(2+) refilling. Inhibition of SR Ca(2+) pump by cyclopiazonic acid dose-dependently suppressed spontaneous SANCs firing up to ≈50%. Cyclopiazonic acid and graded changes in phospholamban phosphorylation produced by β-adrenergic receptor stimulation, phosphodiesterase or protein kinase A inhibition shifted T-90(C) and proportionally shifted the LCR period and spontaneous cycle length (R(2)=0.98).ConclusionsThe LCR period, a critical determinant of the spontaneous SANC cycle length, is defined by the rate of SR Ca(2+) replenishment, which is critically dependent on SR pumping rate, Ca(2+) available for pumping, supplied by L-type Ca(2+) channel, and ryanodine receptor Ca(2+) release flux, each of which is modulated by cAMP-mediated protein kinase A-dependent phosphorylation.

| S-EPMC2941556 | biostudies-literature

Chemical modification of sarcoplasmic reticulum. Stimulation of Ca2+ release.

Project description:Pretreatment of sarcoplasmic membranes with acetic or maleic anhydrides, which interact principally with amino groups, resulted in an inhibition of Ca2+ accumulation and ATPase activity. The presence of ATP, ADP or adenosine 5'-[beta, gamma-imido]triphosphate in the modification medium selectively protected against the inactivation of ATPase activity by the anhydride but did not protect against the inhibition of Ca2+ accumulation. Acetic anhydride modification in the presence of ATP appeared to increase specifically the permeability of the sarcoplasmic reticulum membrane to Ca2+ but not to sucrose, Tris, Na+ or Pi. The chemical modification stimulated a rapid release of Ca2+ from sarcoplasmic reticulum vesicles passively or actively loaded with calcium, from liposomes reconstituted with the partially purified ATPase fraction but not from those reconstituted with the purified ATPase. The inactivation of Ca2+ accumulation by acetic anhydride (in the presence of ATP) was rapid and strongly pH-dependent with an estimated pK value above 8.3 for the reactive group(s). The negatively charged reagents pyridoxal 5-phosphate and trinitrobenzene-sulphonate, which also interact with amino groups, did not stimulate Ca2+ release. Since these reagents do not penetrate the sarcoplasmic reticulum membranes, it is proposed that Ca2+ release is promoted by modification of internally located, positively charged amino group(s).

| S-EPMC1147445 | biostudies-other

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