Evidence for direct involvement of the sarcoplasmic reticulum Ca2+‐ATPase in a passive monovalent cation (K+/Na+) exchange

Jesus, Florence de; Cuillel, Martine; Dupont, Yves

doi:10.1016/0014-5793(95)01267-1

Cited by 3 publications

(2 citation statements)

References 29 publications

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“…The long tail exhibited by the current transients in Fig. 9 for K 1 concentrations $150 mM can be tentatively explained by an uncoupled downhill K 1 translocation due to a carrier-like pump operation, as proposed by Dupont and co-workers (Moutin and Dupont, 1991;de Jesus et al, 1995); in the presence of Ca 21 , this passive transport may only be observed at relatively high K 1 concentrations.…”

Section: K 1 Dependence Of Ca 21 Translocationsupporting

confidence: 57%

“…Thus, it increases the rate of dephosphorylation of the P-E 2 form of Ca-ATPase (Shigekawa and Pearl, 1976;Chaloub and de Meis, 1980) and accelerates both the Ca 21 binding and dissociation in the absence of ATP (Moutin and Dupont, 1991;Orlowski and Champeil, 1991;Lee et al, 1995), suggesting that it increases the rate of the E 2 -E 1 transition. Moreover, it has been proposed that Ca-ATPase catalyzes passive transport of K 1 when the protein is switched to its E 2 conformational state (Moutin and Dupont, 1991;de Jesus et al, 1995). Lee et al (1995) interpreted the effect of K 1 on the binding of Ca 21 to Ca-ATPase by proposing the binding of K 1 to a ''gating'' site, in competition with Mg 21 and H 1 , where it affects the affinity of the calcium pump for Ca 21 ; they also postulated the binding of K 1 to the inner Ca 21 binding site, but not to the outer one.…”

Section: K 1 Dependence Of Ca 21 Translocationmentioning

confidence: 99%

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Time-Resolved Charge Translocation by Sarcoplasmic Reticulum Ca-ATPase Measured on a Solid Supported Membrane

Tadini‐Buoninsegni

Bartolommei

Moncelli

et al. 2004

Biophysical Journal

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Sarcoplasmic reticulum vesicles were adsorbed on an octadecanethiol/phosphatidylcholine mixed bilayer anchored to a gold electrode, and the Ca-ATPase contained in the vesicles was activated by ATP concentration jumps both in the absence and in the presence of K(+) ions and at different pH values. Ca(2+) concentration jumps in the absence of ATP were also carried out. The resulting capacitive current transients were analyzed together with the charge under the transients. The relaxation time constants of the current transients were interpreted on the basis of an equivalent circuit. The current transient after ATP concentration jumps and the charge after Ca(2+) concentration jumps in the absence of ATP exhibit almost the same dependence upon the Ca(2+) concentration, with a half-saturating value of approximately 1.5 microM. The pH dependence of the charge after Ca(2+) translocation demonstrates the occurrence of one H(+) per one Ca(2+) countertransport at pH 7 by direct charge-transfer measurements. The presence of K(+) decreases the magnitude of the current transients without altering their shape; this decrease is explained by K(+) binding to the cytoplasmic side of the pump in the E(1) conformation and being released to the same side during the E(1)-E(2) transition.

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Section: K 1 Dependence Of Ca 21 Translocationsupporting

confidence: 57%

Section: K 1 Dependence Of Ca 21 Translocationmentioning

confidence: 99%

Time-Resolved Charge Translocation by Sarcoplasmic Reticulum Ca-ATPase Measured on a Solid Supported Membrane

Tadini‐Buoninsegni

Bartolommei

Moncelli

et al. 2004

Biophysical Journal

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The cation selectivity of the sarcoball Ca 2+ channel in frog muscle fibres

Ashley

Lea

1998

Pfl�gers Archiv European Journal of Physiology

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We have measured single-channel currents from sarcoplasmic reticulum (SR) blebs (sarcoballs) of frog skeletal muscle fibres using conventional patch-clamp electrodes with excised patches. With both the pipette and bath solutions containing 50 mM Ca(gluconate)2 the slope conductance of the single channels was 39.2 pS for the most commonly seen state, with a reversal potential of -0.4 mV. The cation selectivity of this channel was investigated by replacing the bathing solution with either gluconate or HEPES salts of selected cations. The Goldman permeability ratios, calculated from the reversal potentials, were found to be P(Ca2+)/P(K+)=2.4, P(Ca2+)/ P(Na+)=2.7, P(Ca2+)/P(Tris+)=3.1, P(Ca2+)/P(Mg2+)=1.0 and P(Ca2+)/P(Ba2+)=1.1. Each value for the monovalent ions was found to be less than the corresponding value reported for the SR ryanodine receptor channel from skeletal and cardiac muscle. Single-channel activity could be recorded when the preparation was bathed in symmetrical 50 mM Mg(gluconate)2 solutions, and these channels had a similar conductance and open probability to that measured when the preparation was bathed in symmetrical Ca(gluconate)2 solution. The channel activity in symmetrical 50 mM Ca(gluconate)2 solution was insensitive to bath-applied caffeine (5 mM) and ryanodine (10 microM). The results are in agreement with the conclusion that the sarcoball Ca2+ channel is not the ryanodine receptor release channel, but possibly a form of the SR Ca2+-ATPase which is uncoupled from the catalytic events of the pump and acts as a passive ion channel.

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