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Biomedical subjects

E Ríos

Publications and source records attributed to E Ríos.

At least 55 records · Page 3Linked to original sources
PubMed1993

Effects of perchlorate on the molecules of excitation-contraction coupling of skeletal and cardiac muscle.

To understand the nature of the transmission process of excitation-contraction (EC) coupling, the effects of the anion perchlorate were investigated on the voltage sensor (dihydropyridine receptor, DHPR) and the Ca release channel (ryanodine receptor, RyR) of the sarcoplasmic reticulum (SR). The molecules, from rabbit skeletal muscle, were either separated in membrane vesicular fractions or biochemically purified so that the normal EC coupling interaction was prevented. Additionally, the effect of ClO4- was investigated on L-type Ca2+ channel gating currents of guinea pig ventricular myocytes, as a native DHPR not in the physiological interaction of skeletal muscle. At 20 mM, ClO4- had minor effects on the activation of ionic currents through Ca channels from skeletal muscle transverse tubular (T) membranes fused with planar bilayers: a +7-mV shift in the midpoint voltage, V, with no change in kinetics of activation or deactivation. This is in contrast with the larger, negative shift that ClO4- causes on the distribution of intramembrane charge movement of skeletal muscle. At up to 100 mM it did not affect the binding of the DHP [3H]PN200-110 to triad-enriched membrane fractions (TR). At 8 mM it did not affect the kinetics or the voltage distribution of gating currents of Ca channels in heart myocytes. These negative results were in contrast to the effects of ClO4- on the release channel. At 20 mM it increased several-fold the open probability of channels from purified RyR incorporated in planar bilayers and conducting Ba2+, an effect seen on channels first closed by chelation of Ca2+ or by the presence of Mg2+. It significantly increased the initial rate of efflux of 45Ca2+ from TR vesicles (by a factor of 1.75 at 20 mM and 4.5 at 100 mM). ClO4- also increased the binding of [3H]ryanodine to TR fractions. The relative increase in binding was 50-fold at the lowest [Ca2+] used (1 microM) and then decayed to much lower values as [Ca2+] was increased. The increase was due entirely to an increase in the association rate constant of ryanodine binding. The chaotropic ions SCN- and I- increased the association rate constant to a similar extent. The binding of ryanodine to purified RyR protein reconstituted into liposomes had a greater affinity than to TR fractions but was similarly enhanced by ClO4-. The reducing agent dithiothreitol (5 mM) did not reduce the effect of ClO4-, and 5% polyethylene glycol, with an osmolarity equivalent to 20 mM ClO4-, did not change ryanodine binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

An allosteric model of the molecular interactions of excitation-contraction coupling in skeletal muscle.

A contact interaction is proposed to exist between the voltage sensor of the transverse tubular membrane of skeletal muscle and the calcium release channel of the sarcoplasmic reticulum. This interaction is given a quantitative formulation inspired in the Monod, Wyman, and Changeux model of allosteric transitions in hemoglobin (Monod, J., J. Wyman, and J.-P. Changeux. 1965. Journal of Molecular Biology. 12:88-118), and analogous to one proposed by Marks and Jones for voltage-dependent Ca channels (Marks, T. N., and S. W. Jones. 1992. Journal of General Physiology. 99:367-390). The allosteric protein is the calcium release channel, a homotetramer, with two accessible states, closed and open. The kinetics and equilibrium of this transition are modulated by voltage sensors (dihydropyridine receptors) pictured as four units per release channel, each undergoing independent voltage-driven transitions between two states (resting and activating). For each voltage sensor that moves to the activating state, the tendency of the channel to open increases by an equal (large) factor. The equilibrium and kinetic equations of the model are solved and shown to reproduce well a number of experimentally measured relationships including: charge movement (Q) vs. voltage, open probability of the release channel (Po) vs. voltage, the transfer function relationship Po vs. Q, and the kinetics of charge movement, release activation, and deactivation. The main consequence of the assumption of allosteric coupling is that primary effects on the release channel are transmitted backward to the voltage sensor and give secondary effects. Thus, the model reproduces well the effects of perchlorate, described in the two previous articles, under the assumption that the primary effect is to increase the intrinsic tendency of the release channel to open, with no direct effects on the voltage sensor. This modification of the open-closed equilibrium of the release channel causes a shift in the equilibrium dependency of charge movement with voltage. The paradoxical slowing of charge movement by perchlorate also results from reciprocal effects of the channel on the allosterically coupled voltage sensors. The observations of the previous articles plus the simulations in this article constitute functional evidence of allosteric transmission.

Allosteric Regulation↗
PubMed1993

Ca(2+)-dependent inactivation of cardiac L-type Ca2+ channels does not affect their voltage sensor.

Inactivation of currents carried by Ba2+ and Ca2+, as well as intramembrane charge movement from L-type Ca2+ channels were studied in guinea pig ventricular myocytes using the whole-cell patch clamp technique. Prolonged (2 s) conditioning depolarization caused substantial reduction of charge movement between -70 and 10 mV (charge 1, or charge from noninactivated channels). In parallel, the charge mobile between -70 and -150 mV (charge 2, or charge from inactivated channels) was increased. The availability of charge 2 depended on the conditioning pulse voltage as the sum of two Boltzmann components. One component had a central voltage of -75 mV and a magnitude of 1.7 nC/microF. It presumably is the charge movement (charge 2) from Na+ channels. The other component, with a central voltage of approximately -30 mV and a magnitude of 3.5 nC/microF, is the charge 2 of L-type Ca2+ channels. The sum of charge 1 and charge 2 was conserved after different conditioning pulses. The difference between the voltage dependence of the activation of L-type Ca2+ channels (half-activation voltage, V, of approximately -20 mV) and that of charge 2 (V of -100 mV) made it possible to record the ionic currents through Ca2+ channels and charge 2 in the same solution. In an external solution with Ba2+ as sole metal the maximum available charge 2 of L-type Ca2+ channels was 10-15% greater than that in a Ca(2+)-containing solution. External Cd2+ caused 20-30% reduction of charge 2 both from Na+ and L-type Ca2+ channels. Voltage- and Ca(2+)-dependent inactivation phenomena were compared with a double pulse protocol in cells perfused with an internal solution of low calcium buffering capacity. As the conditioning pulse voltage increased, inactivation monitored with the second pulse went through a minimum at about 0 mV, the voltage at which conditioning current had its maximum. Charge 2, recorded in parallel, did not show any increase associated with calcium entry. Two alternative interpretations of these observations are: (a) that Ca(2+)-dependent inactivation does not alter the voltage sensor, and (b) that inactivation affects the voltage sensor, but only in the small fraction of channels that open, and the effect goes undetected. A model of channel gating that assumes the first possibility is shown to account fully for the experimental results. Thus, extracellular divalent cations modulate voltage-dependent inactivation of the Ca2+ channel. Intracellular Ca2+ instead, appears to cause inactivation of the channel without affecting its voltage sensor.

Animals↗
PubMed1992

Dihydropyridine-sensitive skeletal muscle Ca channels in polarized planar bilayers. 3. Effects of phosphorylation by protein kinase C.

The effects of protein kinase C (PKC) were studied on dihydropyridine (DHP)-sensitive Ca channels from rabbit skeletal muscle T tubule membranes. To determine which channel subunits become phosphorylated under the conditions used for electrophysiological studies, we first performed biochemical studies of phosphorylation. T tubular membranes were fused with vesicles of the lipid mixture used in the planar bilayers, and phosphorylation was assessed using the same concentrations of PKC, adenosine 5'-triphosphate, and buffers as were used in the electrophysiological experiments. The alpha 1 subunit of the DHP receptors was phosphorylated by PKC to an extent of 1 mol phosphate/mol protein. The beta subunit was also phosphorylated but to a significantly lesser extent. The DHP-sensitive Ca channel activity was studied after fusing T tubule membranes with planar bilayers (Ma, J., C. Mundiña-Weilenmann, M. M. Hosey, and E. Ríos. 1991. Biophys. J. 60:890-901). The bilayers were held at -80 mV and activated by depolarizing voltage clamp pulses. The observed Ca channels exhibited two open states (tau o1 = 5 ms and tau o2 = 25 ms). On addition of purified PKC to the intracellular side, the proportion of the longer open state increased threefold. The average open probability during a 2-s, maximally activating pulse (Pmax) increased from 10 to 15%. The voltage dependence of activation was not changed by PKC; the Boltzmann parameters were V1 = -20.5 mV and K = 10.5 mV, which were not significantly different from the reference channels. The deactivation (closing) time constant was increased from 7 to 12 ms after PKC. The inactivation time constant during the pulse was slightly increased(from 1.2 to 1.6 s), and the channel availability at the holding potential was decreased from 76 to 71%. Taken together, the results revealed that PKC increased Pmax largely through a shift in the voltage independent open-close equilibrium of the fully activated channels.This is in contrast with the effect of phosphorylation by PKA (Mundir'a-Weilenmann, C., J. Ma, E. Rios, and M. M. Hosey. 1991. Biophys.J. 60:902-909), which also increases Pmax but mostly by increasing the availability of channels and slowing inactivation during the pulse.

Animals↗
PubMed1992

Two classes of gating current from L-type Ca channels in guinea pig ventricular myocytes.

Intramembrane charge movement was recorded in guinea pig ventricular myocytes at 19-22 degrees C using the whole-cell patch clamp technique. From a holding potential of -110 mV, the dependence of intramembrane charge moved on test voltage (Q(V)) followed the sum of two Boltzmann components. One component had a transition voltage (V) of -48 mV and a total charge (Qmax) of congruent to 3 nC/microF. The other had a V of -18 mV and a Qmax of 11 nC/microF. Ba2+ currents through Ca channels began to activate at -45 mV and peaked at congruent to -15 mV. Na+ current peaked at -35 to -30 mV. Availability of charge (in pulses from -70 to +10 mV) depended on the voltage of conditioning depolarizations as two Boltzmann terms plus a constant. One term had a V of -88 mV and a Qmax of 2.5 nC/microF; the other had a V of -29 mV and a Qmax of 6.3 nC/microF. From the Q(V) dependence, the voltage dependence of the ionic currents, and the voltage dependence of the availability of charge, the low voltage term of Q(V) and availability was identified as Na gating charge, at a total of 3.5 nC/microF. The remainder, 11 nC/microF, was attributed to Ca channels. After pulses to -40 mV and above, the OFF charge movement had a slow exponentially decaying component. Its time constant had a bell-shaped dependence on OFF voltage peaking at 11 ms near -100 mV. Conditioning depolarizations above -40 mV increased the slow component exponentially with the conditioning duration (tau approximately equal to 480 ms). Its magnitude was reduced as the separation between conditioning and test pulses increased (tau approximately equal to 160 ms). The voltage distribution of the slow component of charge was measured after long (5 s) depolarizations. Its V was -100 mV, a shift of -80 mV from the value in normally polarized cells. This voltage was the same at which the time constant of the slow component peaked. Qmax and the steepness of the voltage distribution were unchanged by depolarization. This indicates that the same molecules that produce the charge movement in normally polarized cells also produce the slow component in depolarized cells. 100 microns D600 increased by 77% the slow charge movement after a 500-ms conditioning pulse. These results demonstrate two classes of charge movement associated with L-type Ca channels, with kinetics and voltage dependence similar to charge 1 and charge 2 of skeletal muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Differential effects of tetracaine on two kinetic components of calcium release in frog skeletal muscle fibres.

1. Intramembrane charge movements and changes in intracellular calcium concentration were recorded simultaneously in voltage clamped cut skeletal muscle fibres of the frog in the presence and absence of tetracaine. 2. Extracellular application of 20 microM tetracaine reduced the increase in myoplasmic [Ca2+]. The effect on the underlying calcium release flux from the sarcoplasmic reticulum was to suppress the peak of the release while sparing the steady level attained at the end of 100 ms clamp depolarizations. 3. While the peak of the release flux at corresponding voltages was reduced by 62% after the addition of tetracaine, the rate of inactivation was the same when the pulses elicited release fluxes of similar amplitude. 4. Higher concentrations of tetracaine, 0.2 mM, abolished the calcium signal in stretched fibres whereas in slack fibres this concentration left a non-inactivating calcium release flux. 5. Lowering the extracellular pH antagonized the effect of the drug both on charge movements and on calcium signals. The permanently charged analogue tetracaine methobromide lacked effects on excitation-contraction coupling. 6. These results imply that the two kinetic components of calcium release flux have very different tetracaine sensitivities. They are also consistent with an intracellular site of action of the drug at low concentration. Taken together they strongly suggest that the inactivating and non-inactivating components of calcium release correspond to different pathways: one that inactivates, is sensitive to tetracaine and is controlled by calcium, and another that does not inactivate, is much less sensitive to tetracaine and is directly controlled by voltage.

Action Potentials↗
PubMed1992

Charge movement and the nature of signal transduction in skeletal muscle excitation-contraction coupling.

The mechanism of transmission remains unclear. It is possible that release is reinforced by Ca(2+)-induced activation secondary to opening of release channels by another primary mechanism. Multiple results favor some function of IP3 in EC coupling; however, there are many arguments indicating that IP3 is not the primary transmitter. DHP receptors and ryanodine receptors are known to play essential roles in the triadic junction, but the biochemical make up of the junction has not been completely established, and there may be other essential proteins. The strongest argument in favor of mechanical coupling between voltage sensor and release channel is the close proximity of the channel protein to the T membrane and the fixed stoichiometry between sensors and channels.

Animals↗
PubMed1991

The mechanical hypothesis of excitation-contraction (EC) coupling in skeletal muscle.

The mechanism of transmission in skeletal muscle EC coupling is still an open question. There is some indirect evidence in favour of the mechanical coupling hypothesis, deriving mostly from consideration of the structure of the Ca2+ release channel protein. A new functional approach is proposed, that consists in comparing the properties of the complete system--EC coupling in a skeletal muscle fibre--with those of the EC coupling molecules in bilayers. In this approach, those properties of the whole system that are not traceable to its constitutive molecules, are ascribed to the physiological interaction, and are expected to yield new information on the nature of this interaction.

Animals↗
PubMed1991

Dihydropyridine-sensitive skeletal muscle Ca channels in polarized planar bilayers. 1. Kinetics and voltage dependence of gating.

Rabbit skeletal muscle transverse tubule (T) membranes were fused with planar bilayers. Ca channel activity was studied with a "cellular" approach, using solutions that were closer to physiological than in previous studies, including asymmetric extracellular divalent ions as current carriers. The bilayer was kept polarized at -80 mV and depolarizing pulses were applied under voltage clamp. Upon depolarization the channels opened in a steeply voltage-dependent manner, and closed rapidly at the end of the pulses. The activity was characterized at the single-channel level and on macroscopic ensemble averages of test-minus-control records, using as controls the null sweeps. The open channel events had one predominant current corresponding to a conductance of 9 pS (100 mM Ba2+). The open time histogram was fitted with two exponentials, with time constants of 5.8 and 30 ms (23 degrees C). Both types of events were virtually absent at -80 mV. The average open probability (fractional open time) increased sigmoidally from 0 to a saturation level of 0.08, following a Boltzmann function centered at -25 mV and with a steepness factor of 7 mV. Ensemble averages of test-minus-control currents showed a sigmoidal activation followed by inactivation during the pulse and deactivation (closing) after the pulse. The ON time course was well fitted with "m3h" kinetics, with tau m = 120 ms and tau h = 1.2 s. Deactivation was exponential with tau = 8 ms. This study demonstrates a technique for obtaining Ca channel events in lipid bilayers that are strictly voltage dependent and exhibit most of the features of the macroscopic ICa. The technique provides a useful approach for further characterization of channel properties, as exemplified in the accompanying paper, that describes the consequences on channel properties of phosphorylation by cAMP dependent protein kinase.

Animals↗
PubMed1991

Dihydropyridine-sensitive skeletal muscle Ca channels in polarized planar bilayers. 2. Effects of phosphorylation by cAMP-dependent protein kinase.

The effects of phosphorylation on the voltage-dependent properties of dihydropyridine-sensitive Ca channels of skeletal muscle were studied. Single channel currents were recorded upon incorporation of transverse tubule membranes into planar bilayers that were kept polarized at near physiological resting potential and subjected to depolarizing pulses under voltage clamp. Studies were conducted to analyze the properties of the channels at both the single channel and macroscopic level, using methods introduced in the preceding paper (Ma et al., 1991. Biophys. J. 60: 890-901.). Addition of the catalytic subunit of cAMP-dependent protein kinase to the cis (intracellular) side of the bilayers containing channels resulted in: (a) an increase in open channel probability at all voltages above -50 mV; (b) a leftward shift (by 7 mV) in the curve describing the voltage-dependence of activation; (c) an approximate twofold decrease in the rate of inactivation; and (d) an increase in the availability of the channel. These findings provide new insights at the single channel level into the mechanism of modulation of the dihydropyridine-sensitive Ca channels of skeletal muscle by signal transduction events that involve elevation in cAMP and activation of the cAMP-dependent protein kinase.

Animals↗
PubMed1991

Interfering with calcium release suppresses I gamma, the "hump" component of intramembranous charge movement in skeletal muscle.

Four manifestations of excitation-contraction (E-C) coupling were derived from measurements in cut skeletal muscle fibers of the frog, voltage clamped in a Vaseline-gap chamber: intramembranous charge movement currents, myoplasmic [Ca2+] transients, flux of calcium release from the sarcoplasmic reticulum (SR), and the intrinsic optical transparency change that accompanies calcium release. In attempts to suppress Ca release by direct effects on the SR, three interventions were applied: (a) a conditioning pulse that causes calcium release and inhibits release in subsequent pulses by Ca-dependent inactivation; (b) a series of brief, large pulses, separated by long intervals (greater than 700 ms), which deplete Ca2+ in the SR; and (c) intracellular application of the release channel blocker ruthenium red. All these reduced calcium release flux. None was expected to affect directly the voltage sensor of the T-tubule; however, all of them reduced or eliminated a component of charge movement current with the following characteristics: (a) delayed onset, peaking 10-20 ms into the pulse; (b) current reversal during the pulse, with an inward phase after the outward peak; and (c) OFF transient of smaller magnitude than the ON, of variable polarity, and sometimes biphasic. When the total charge movement current had a visible hump, the positive phase of the current eliminated by the interventions agreed with the hump in timing and size. The component of charge movement current blocked by the interventions was greater and had a greater inward phase in slack fibers with high [EGTA] inside than in stretched fibers with no EGTA. Its amplitude at -40 mV was on average 0.26 A/F (SEM 0.03) in slack fibers. The waveform of release flux determined from the Ca transients measured simultaneously with the membrane currents had, as described previously (Melzer, W., E. Ríos, and M. F. Schneider. 1984. Biophysical Journal. 45:637-641), an early peak followed by a descent to a steady level during the pulse. The time at which this peak occurred was highly correlated with the time to peak of the current suppressed, occurring on average 6.9 ms later (SEM 0.73 ms). The current suppressed by the above interventions in all cases had a time course similar to the time derivative of the release flux; specifically, the peak of the time derivative of release flux preceded the peak of the current suppressed by 0.7 ms (SEM 0.6 ms). The magnitude of the current blocked was highly correlated with the inhibitory effect of the interventions on Ca2+ release flux.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Effect of the calcium buffer EGTA on the "hump" component of charge movement in skeletal muscle.

Three manifestations of excitation-contraction (E-C) coupling were measured in cut skeletal muscle fibers of the frog, voltage clamped in a double Vaseline gap: intramembrane charge movements, myoplasmic Ca2+ transients, and changes in optical transparency. Pulsing patterns in the presence of high [EGTA] intracellularly, shown by García et al. (1989. J. Gen. Physiol. 94:973-986) to deplete Ca2+ in the sarcoplasmic reticulum, were found to change the above manifestations. With an intracellular solution containing 15 mM EGTA and 0 Ca, 10-15 pulses (100 ms) to -20 mV at a frequency of 2 min-1 reduced the "hump" component of charge movement current. This effect was reversible by 5 min of rest. The same effect was obtained in 62.5 mM EGTA and 0 Ca by pulsing at 0.2 min-1. This effect was reversible by adding calcium to the EGTA solution, for a nominal [Ca2+]i of 200 nM, and was prevented by adding calcium to the EGTA solution before pulsing. The suppression of the hump was accompanied by elimination of the optical manifestations of E-C coupling. The current suppressed was found by subtraction and had the following properties: delayed onset, a peak at a variable interval (10-20 ms) into the pulse, a negative phase (inward current) after the peak, and a variable OFF transient that could be multi-phasic and carried less charge than the ON transient. In the previous paper (Csernoch et al., 1991. J. Gen. Physiol. 97:845-884) it was shown that several interventions suppress a similar component of charge movement current, identified with the "hump" or Q gamma current (I gamma). Based on the similarity to that component, the charge movement suppressed by the depletion protocols can also be identified with I gamma. The fact that I gamma is suppressed by Ca2+ depletion and the kinetic properties of the charge suppressed is inconsistent with the existence of separate sets of voltage sensors underlying the two components of charge movement, Q beta and Q gamma. This is explicable if Q gamma is a consequence of calcium release from the sarcoplasmic reticulum.

Animals↗
PubMed1991

The relationship between Q gamma and Ca release from the sarcoplasmic reticulum in skeletal muscle.

Asymmetric membrane currents and fluxes of Ca2+ release were determined in skeletal muscle fibers voltage clamped in a Vaseline-gap chamber. The conditioning pulse protocol 1 for suppressing Ca2+ release and the "hump" component of charge movement current (I gamma), described in the first paper of this series, was applied at different test pulse voltages. The amplitude of the current suppressed during the ON transient reached a maximum at slightly suprathreshold test voltages (-50 to -40 mV) and decayed at higher voltages. The component of charge movement current suppressed by 20 microM tetracaine also went through a maximum at low pulse voltages. This anomalous voltage dependence is thus a property of I gamma, defined by either the conditioning protocol or the tetracaine effect. A negative (inward-going) phase was often observed in the asymmetric current during the ON of depolarizing pulses. This inward phase was shown to be an intramembranous charge movement based on (a) its presence in the records of total membrane current, (b) its voltage dependence, with a maximum at slightly suprathreshold voltages, (c) its association with a "hump" in the asymmetric current, (d) its inhibition by interventions that reduce the "hump", (e) equality of ON and OFF areas in the records of asymmetric current presenting this inward phase, and (f) its kinetic relationship with the time derivative of Ca release flux. The nonmonotonic voltage dependence of the amplitude of the hump and the possibility of an inward phase of intramembranous charge movement are used as the main criteria in the quantitative testing of a specific model. According to this model, released Ca2+ binds to negatively charged sites on the myoplasmic face of the voltage sensor and increases the local transmembrane potential, thus driving additional charge movement (the hump). This model successfully predicts the anomalous voltage dependence and all the kinetic properties of I gamma described in the previous papers. It also accounts for the inward phase in total asymmetric current and in the current suppressed by protocol 1. According to this model, I gamma accompanies activating transitions at the same set of voltage sensors as I beta. Therefore it should open additional release channels, which in turn should cause more I gamma, providing a positive feedback mechanism in the regulation of calcium release.

Animals↗
PubMed1991

Familial alloimmune neutropenia of NA-2 specificity.

Three siblings with alloimmune neonatal neutropenia are presented. An immunoglobulin G (IgG) antineutrophil antibody specific for NA-2 antigen was demonstrated in maternal serum and in both of the three affected infants who were studied as neonates. The mother's neutrophils were negative for NA-2 antigen. The father and all four children, including the three known to be affected, had neutrophils that expressed NA-2 antigen. One patient studied sequentially demonstrated an inverse relationship between the antineutrophil antibody titer and the absolute neutrophil count. Exchange transfusions did not appear to benefit two of the infants.

Antibody Specificity↗
PubMed1989

The voltage sensor of excitation-contraction coupling in skeletal muscle. Ion dependence and selectivity.

Manifestations of excitation-contraction (EC) coupling of skeletal muscle were studied in the presence of metal ions of the alkaline and alkaline-earth groups in the extracellular medium. Single cut fibers of frog skeletal muscle were voltage clamped in a double Vaseline gap apparatus, and intramembrane charge movement and myoplasmic Ca2+ transients were simultaneously measured. In metal-free extracellular media both charge movement of the charge 1 type and Ca transients were suppressed. Under metal-free conditions the nonlinear charge distribution was the same in depolarized (holding potential of 0 mV) and normally polarized fibers (holding potentials between -80 and -90 mV). The manifestations of EC coupling recovered when ions of groups Ia and IIa of the periodic table were included in the extracellular solution; the extent of recovery depended on the ion species. These results are consistent with the idea that the voltage sensor of EC coupling has a binding site for metal cations--the "priming" site--that is essential for function. A state model of the voltage sensor in which metal ligands bind preferentially to the priming site when the sensor is in noninactivated states accounts for the results. This theory was used to derive the relative affinities of the various ions for the priming site from the magnitude of the EC coupling response. The selectivity sequence thus constructed is: Ca greater than Sr greater than Mg greater than Ba for group IIa cations and Li greater than Na greater than K greater than Rb greater than Cs for group Ia. Ca2+, the most effective of all ions tested, was 1,500-fold more effective than Na+. This selectivity sequence is qualitatively and quantitatively similar to that of the intrapore binding sites of the L-type cardiac Ca channel. This provides further evidence of molecular similarity between the voltage sensor and Ca channels.

Animals↗
PubMed1989

[Familial lead poisoning].

A 1 year and 9 month old patient was admitted with ataxia. CBC showed a microcytic, hypocromic anemia with intense basophilic sttipling of erythrocytes. Lead poisoning was suspected and confirmed with a blood lead level of 167 micrograms/dl. The patient was treated with EDTA and BAL. It was discovered that family burned old car batteries for food cooking. Four members were intoxicated, with blood lead levels at or above 50 micrograms/dl.

Adolescent↗