Cyclophosphamide alters the clinical and pathological expression of experimental autoimmune gray matter disease

Guinea pigs inoculated with bovine spinal cord ventral horn homogenate develop a syndrome termed experimental autoimmune gray matter disease (EAGMD) characterized by extremity weakness, bulbar signs, and a loss of lower and upper motoneurons. To provide evidence for the role of autoimmune mechanisms, we have administered the immunosuppressant cyclophosphamide prior to and after gray matter immunization. Pretreatment with cyclophosphamide prevented the appearance of clinical signs of disease and decreased the loss of spinal cord motoneurons, the appearance of damaged motoneurons, and the antibody titer to motoneurons. Treatment 7 days after immunization attenuated the expression of disease. Treatment immediately after signs also improved the clinical and pathological findings. In all cyclophosphamide-treated animals there was less IgG within motoneurons and less inflammation. These results support the role for autoimmune mechanisms in motoneuron loss and degeneration in EAGMD.

Molecular basis of gating charge immobilization in Shaker potassium channels

Voltage-dependent ion channels respond to changes in the membrane potential by means of charged voltage sensors intrinsic to the channel protein. Changes in transmembrane potential cause movement of these charged residues, which results in conformational changes in the channel. Movements of the charged sensors can be detected as currents known as gating currents. Measurement of the gating currents of the Drosophila Shaker potassium channel indicates that the charge on the voltage sensor of the channels is progressively immobilized by prolonged depolarizations. The charge is not immobilized in a mutant of the channel that lacks inactivation. These results show that the region of the molecule responsible for inactivation interacts, directly or indirectly, with the voltage sensor to prevent the return of the charge to its original position. The gating transitions between closed states of the channel appear not to be independent, suggesting that the channel subunits interact during activation.

Evidence for direct interaction of Gs alpha with the Ca2+ channel of skeletal muscle

The alpha subunits of heterotrimeric GTP-binding (G) proteins act upon ion channels through both cytoplasmic and membrane-delimited pathways (Brown, A. M., and Birnbaumer, L. (1990) Annu. Rev. Physiol. 52, 197-213). The membrane pathway may involve either a direct interaction between G protein and ion channel or an indirect interaction involving a membrane-delimited second messenger. To distinguish between the two possibilities, we tested whether a purified G protein could interact with a purified channel protein in a defined system to produce changes in channel currents. We selected the alpha subunit of Gs and the dihydropyridine (DHP)-sensitive Ca2+ channel of skeletal muscle T-tubules, the DHP binding protein (DHPBP), because: 1) a membrane-delimited interaction between the two has been shown (Brown, A. M., and Birnbaumer, L. (1990) Annu. Rev. Physiol. 52, 197-213; Yatani, A., Imoto, Y., Codina, J., Hamilton, S. L., Brown, A. M., and Birnbaumer, L. (1988) J. Biol. Chem. 263, 9887-9895); and 2) at the present time, these Ca2+ channels are the only putative G protein channel effectors which, following purification, still retain channel function. We used a defined system in which purified components were studied by direct reconstitution in planar lipid bilayers. Just as we had found in crude skeletal muscle T-tubule membranes (Yatani, A., Imoto, Y., Codina, J., Hamilton, S. L., Brown, A. M., and Birnbaumer, L. (1988) J. Biol. Chem. 263, 9887-9895), alpha*s but not alpha*i-3 stimulated Ca2+ currents. However, in the reconstituted system, this probably represents a direct interaction between Gs alpha and Ca2+ channels. To establish whether the two proteins were physically associated in the native T-tubule membrane, we examined the ability of either endogenous G proteins or exogenous alpha*s to purify with detergent-solubilized DHPBP through a wheat germ agglutinin affinity column and a sucrose gradient. Small amounts of a labeled G protein were found to co-purify with DHPBP. In addition, partially purified DHPBP increased the sedimentation rate of purified alpha*s but not alpha*i-3. G proteins were immunoprecipitated with an antibody to the alpha 1 subunit of the DHPBP, and, in addition, both alpha s and the beta subunit of Gs were detected in Western blots of the partially purified DHPBP. The results suggest that Gs and Ca2+ channels are closely associated in the T-tubule plasma membrane, and we conclude that skeletal muscle Ca2+ channels are direct effectors for Gs.

Calcium-activated K+ channels: metabolic regulation

Calcium-activated potassium (KCa) channels are highly modulated by a large spectrum of metabolites. Neurotransmitters, hormones, lipids, and nucleotides are capable of activating and/or inhibiting KCa channels. Studies from the last few years have shown that metabolites modulate the activity of KCa channels via: (1) a change in the affinity of the channel for Ca2+ (K 1/2 is modified), (2) a parallel shift in the voltage axis of the activation curves, or (3) a change in the slope (effective valence) of the voltage dependence curve. The shift of the voltage dependence curve can be a direct consequence of the change in the affinity for Ca2+. Recently, the mechanistic steps involved in the modulation of KCa channels are being uncovered. Some interactions may be direct on KCa channels and others may be mediated via G-proteins, second messengers, or phosphorylation. The information given in this review highlights the possibility that KCa channels can be activated or inhibited by metabolites without a change in the intracellular Ca2+ concentration.

Potassium currents in freshly dispersed myometrial cells

K+ currents in freshly dispersed cells from rat myometrium at estrus were studied with the patch-clamp technique (whole cell). Three types of K+ currents were identified: 1) a fast-activating current (IKf), 2) a slowly activating current (IKs), and 3) a transient current (IKt). IKf had a half-activation voltage of 12 mV and a time constant of activation (tau on) of approximately 3 ms at +50 mV. IKs had a tau on of approximately 9 ms at +50 mV and a half-activation potential of 33 mV. Both IKf and IKs were sustained and became potentiated by the entrance of Ca2+ from the patch pipette. These two Ca(2+)-activated K+ currents were inhibited by 100 nM external charybdotoxin and were blocked by external tetraethylammonium (TEA, 2-20 mM). The third current (IKt) was transient, had a faster tau on (approximately 1 ms), and a decay phase with a time constant of approximately 8 ms at +50 mV. This current had a half-activation potential of 22 mV. IKt was not potentiated by intracellular Ca2+, was sensitive to 4-aminopyridine (1 mM), was insensitive to external charybdotoxin (100 nM) and TEA (2 mM), and spontaneously decreased with time.

Calcium-activated potassium channels from coronary smooth muscle reconstituted in lipid bilayers

This work is the initial characterization of Ca(2+)-activated K+ (KCa) channels from coronary smooth muscle reconstituted into lipid bilayers. The channels were obtained from a surface membrane preparation of porcine coronary smooth muscle. KCa channels were the predominant K+ channels in this preparation. The conductance histogram (n = 137 channels) revealed two main populations of "maxi" KCa channels with conductances of 245 and 295 pS. Each population could be subdivided in two "isoforms" or "isochannels" with different functional properties (voltage and Ca2+ sensitivities and kinetics). The analysis of "burst" probability of opening showed that at pCa 4 the two isochannels of 245 pS (KCa-1 and KCa-1') had half-activation potentials (V1/2) of -80 and 6 mV, respectively. The isochannels of 295 pS (KCa-2 and KCa-2') had V1/2 of -28 and -66 mV, respectively. KCa-1 had the highest Ca2+ sensitivity; at -60 mV, the concentration of half-activation value for Ca2+ was 1.2 +/- 0.3 microM (n = 5). External tetraethylammonium reduced channel amplitude in a voltage-dependent manner; dissociation constant was 180 +/- 6 and 466 +/- 41 microM at -40 and +80 mV, respectively (n = 5). Charybdotoxin (5-50 nM) produced typical long closings. These effects were similar in all the channels. We conclude that coronary smooth muscle possesses isoforms of maxi KCa channels with Ca2+ and voltage sensors with different properties, which may confer to each channel a specific functional role.

IgG from amyotrophic lateral sclerosis affects tubular calcium channels of skeletal muscle

Amyotrophic lateral sclerosis (ALS) is a devastating human disease of upper and lower motoneurons. We studied the action of the immunoglobulin G (IgG) from ALS and disease control patients on dihydropyridine (DHP)-sensitive Ca2+ channels in single mammalian skeletal muscle fibers with the double Vaseline gap technique. The peak of the Ca2+ current (ICa) and the charge movement were reduced when the fibers were incubated in ALS IgG. These effects were lost when the IgG was boiled or adsorbed with skeletal tubular membranes. ALS IgG reduced skeletal muscle ICa in a similar fashion as nifedipine; the ICa blockade was voltage dependent, and the associated charge movement was reduced. These observations suggest that IgG from ALS patients reacts with the skeletal muscle DHP-sensitive Ca2+ channels or some associated regulatory moiety.

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.

Abnormal human sarcoplasmic reticulum Ca2+ release channels in malignant hyperthermic skeletal muscle

Single sarcoplasmic reticulum (SR) Ca2+ release channels were reconstituted from normal and malignant hyperthermic (MH) human skeletal muscle biopsies (2-5 g samples). Conduction, gating properties, and myoplasmic Ca2+ dependence of human SR Ca2+ release channels were similar to those in other species (rabbit, pig). The MH diagnostic procedure distinguishes three phenotypes (normal, MH-equivocal, and MH-susceptible) on the basis of muscle contracture sensitivity to caffeine and/or halothane. Single channel studies reveal that human MH muscles (both MH phenotypes) contain SR Ca2+ release channels with abnormally greater caffeine sensitivity. Muscles from MH-equivocal and MH-susceptible patients appear to contain channels with the same abnormality. Further, our data (n = 115, 21 channels, 11 patients) reveals that human MH muscles (both phenotypes) may contain two populations of SR Ca2+ release channels, possibly corresponding to normal and abnormal isoforms. Thus, whole cell phenotypic variation (MH-equivocal vs. MH-susceptible) arises in muscles containing channels with similar caffeine sensitivity suggesting that human MH does not arise from a single defect. These results have important ramifications concerning (a) correlation of functional and genetic MH studies, (b) identification of other, yet to be determined, factors which may influence MH expression, and (c) characterization of normal SR Ca2+ release channel function by exploring genetic channel defects.

Phosphatidylinositol 4,5-bisphosphate-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum terminal cisternal membranes. Ca2+ flux and single channel studies

We report here that the inositol 1,4,5-trisphosphate (IP3) precursor, L-alpha-phosphatidylinositol 4,5-bisphosphate (PIP2) is a potent molecule (1 microM) which activates the ryanodine-sensitive Ca2+ release channel from rabbit skeletal muscle terminal cisternae incorporated into a phospholipid bilayer. It also stimulates Ca2+ release from these membrane vesicles. Therefore, it may play a modulating role in excitation-contraction coupling. In the bilayer, PIP2 added on the cytoplasmic side increased the mean channel opening probability 2-12-fold in the presence and absence of physiological Mg2+ and ATP. From flux studies, PIP2-induced Ca2+ release, occurring through the ryanodine-sensitive Ca2+ release channel, displayed saturation kinetics. The rate of Ca2+ release induced by PIP2 was approximately greater than 50% slower than the rates induced by other agents (e.g. caffeine, Ca2+, ATP). PIP2, and not IP3, effectively elicited Ca2+ release from terminal cisternae. On the contrary, IP3, and not PIP2, specifically mediated Ca2+ release from dog brain cerebellum microsomes, where IP3 receptors are known to be found. The PIP2-induced Ca2+ release from muscle membranes was not dependent on medium [Ca2+] (from less than 10(-9) to approximately 10(-4) M). However, IP3 could activate the terminal cisternae Ca2+ channel in the bilayer when there was low Ca2+ (less than 10(-7) M). The data suggest that the ionic microenvironment around the Ca2+ channel may be different for observing the two phosphoinositide actions.

Voltage-dependent inactivation of T-tubular skeletal calcium channels in planar lipid bilayers

Single-channel properties of dihydropyridine (DHP)-sensitive calcium channels isolated from transverse tubular (T-tube) membrane of skeletal muscle were explored. Single-channel activity was recorded in planar lipid bilayers after fusion of highly purified rabbit T-tube microsomes. Two populations of DHP-sensitive calcium channels were identified. One type of channel (noninactivating) was active (2 microM +/- Bay K 8644) at steady-state membrane potentials and has been studied in other laboratories. The second type of channel (inactivating) was transiently activated during voltage pulses and had a very low open probability (Po) at steady-state membrane potentials. Inactivating channel activity was observed in 47.3% of the experiments (n = 84 bilayers). The nonstationary kinetics of this channel was determined using a standard voltage pulse (HP = -50 mV, pulse to 0 mV). The time constant (tau) of channel activation was 23 ms. During the mV). The time constant (tau) of channel activation was 23 ms. During the pulse, channel activity decayed (inactivated) with a tau of 3.7 s. Noninactivating single-channel activity was well described by a model with two open and two closed states. Inactivating channel activity was described by the same model with the addition of an inactivated state as proposed for cardiac muscle. The single-channel properties were compared with the kinetics of DHP-sensitive inward calcium currents (ICa) measured at the cellular level. Our results support the hypothesis that voltage-dependent inactivation of single DHP-sensitive channels contributes to the decay of ICa.

Antibodies as probes for ligand gating of single sarcoplasmic reticulum Ca2(+)-release channels

A large (565 kDa) junctional sarcoplasmic reticulum (SR) protein, the ryanodine receptor (RYR), may play both a structural and a functional role in the mechanism of skeletal muscle excitation-contraction coupling. Recently, the primary amino acid sequence of the RYR has been elucidated. In this paper, we introduce an immunological approach to examine the functional (electrophysiological) properties of the RYR when it is incorporated into planar lipid bilayers. The effects of two polyclonal antibodies against the SR junctional face membrane (JFM) and the RYR (anti-JFM and anti-RYR) were tested on the single-channel gating properties of the RYR SR Ca2(+)-release channel. Junctional SR vesicles were fused into planar lipid bilayers in solutions containing caesium salts. Solutions were designed to minimize the background conductances of the SR K+ and Cl- channels. Three actions of the anti-JFM antibody were distinguished on the basis of single-channel gating and conductance. The anti-RYR antibody had a single action, a simultaneous decrease in single-channel open probability (Po) and conductance. Both antibodies appear to alter single-channel gating by disrupting the Ca2(+)-activation mechanism of the channel. Anti-RYR-antibody-induced gating abnormalities were reversed by ATP, although the ATP-re-activated channels had altered gating kinetics. Two antigenic regions, recognizing the anti-RYR antibody, in the C-terminal end of the RYR primary amino acid sequence contain or are closely associated with putative ligand (Ca2+ and ATP)-binding sites identified previously. Our results demonstrate (1) that the antibodies induced abnormal gating (decreased open probability and stabilization of subconducting states) of SR release channels, and (2) that abnormal gating is not associated with physical obstruction or alteration of the conduction pathway. Thus antibodies directed at specific regions of the RYR (e.g. putative ligand-binding sites) can be used as effective probes with which to study the structural and functional properties of the SR Ca2(+)-release channel gating at the single-channel level.

Differential effects of ryanodine and tetracaine on charge movement and calcium transients in frog skeletal muscle

1. Charge movement and myoplasmic calcium transients were simultaneously recorded from frog skeletal muscle fibres by using the double-seal Vaseline-gap technique. Calcium transients were monitored with the fluorescent indicator Rhod-2. 2. Ryanodine modified the kinetics and the total amount of charge moved during depolarizing pulses (Q(on)), while it did not significantly modify the charge after repolarization (Q(off)). The extracellular application of 100 microM-ryanodine elicited a temporary initial increase of the delayed component of charge movement (Q gamma) and the calcium transient. Both phenomena were later blocked with the same temporal course and to the same extent. 3. The blockade of Q gamma and the calcium transient was also observed with ryanodine concentrations of 1-10 microM. For membrane potentials positive to -10mV, the Qon measured was larger in the presence of ryanodine; Qoff was not modified. 4. Tetracaine (400-500 microM) blocked a similar delayed component of Qon, identified as Q gamma, as well as the calcium transient monitored simultaneously. This effect was observed in the first minutes after the addition of tetracaine to the extracellular solution. 5. Tetracaine blocked a faster initial component of Qon for voltages positive to -10 mV, corresponding to the voltage range of activation of the calcium current. At these same membrane potentials, Qoff was also reduced to a similar extent to Qon. 6. Ryanodine and tetracaine showed different effects on calcium current. Whereas the slow calcium current was not modified upon the addition of ryanodine, it was completely blocked in the presence of tetracaine. The blockade of the slow calcium current made evident the fast calcium current. The effects of tetracaine on the charge movement, the calcium transient and the slow calcium current were reversible. 7. These results suggest that ryanodine and tetracaine may act at different sites. Ryanodine exerts its effect on the sarcoplasmic reticulum ryanodine receptor, blocking calcium release and Q gamma, while tetracaine at these concentrations may affect the release channel and the dihydropyridine receptor, causing a blockade of the charge movement, calcium transient and calcium current.

Charge movement and calcium currents in skeletal muscle fibers are enhanced by GTP gamma S

G-proteins play several regulatory roles in the cell. They can modulate ionic channels directly or in association with second messengers. In skeletal muscle, G-proteins modulate the activity of calcium channels either by acting directly on the channel and/or through a cAMP-dependent phosphorylating mechanism. The activation of G-proteins by GTP gamma S can also induce force generation in skinned fibers. In this paper we studied the effect of GTP gamma S on charge movement and calcium currents (ICa) in rat and frog skeletal muscle, using the Vaseline gap technique. We observed an increase in both charge movement and ICa after the intracellular addition of 10-100 microM GTP gamma S. GDP beta S did not have any effect. Addition of protein kinase A catalytic subunit increased the ICa, probably through a phosphorylation process, but did not modify the charge movement. This suggests that protein kinase A and GTP gamma S are acting on different sites of the channel. It can be speculated that G-proteins may have a regulatory role in the excitation-contraction coupling mechanism by a direct effect on charge movement.

Increased MEPP frequency as an early sign of experimental immune-mediated motoneuron disease

Intracellular recordings of miniature end-plate potentials were performed in extensor digitorum longus muscles from guinea pigs with experimental immune-mediated motoneuron destruction. In the early stages of the disease, the miniature end-plate potential frequency was elevated compared to that in control and normal animals. The amplitude and time course of the miniature end-plate potentials as well as the resting potential of the muscle fibers were not altered, which implies integrity of the postjunctional membrane. The increase in frequency of miniature end-plate potential reflects an increase of basal acetylcholine release and documents dysfunction of the presynaptic terminal of the neuromuscular junction. The increased frequency was associated with high levels of antimotoneuronal IgG in the blood and the presence of IgG at motor end-plates. These data suggest that the presynaptic terminal of the neuromuscular junction may be involved in the immune attack in animal models of motoneuron degeneration.

Functional studies of Ca2+ channels from plasmalemma and sarcoplasmic reticulum membranes in muscle cells

Physiological and biochemical studies (channel characteristics, intracellular Ca2+ determinations and, channel purification, cloning and expression) of the different components involved in the regulation of intercellular Ca2+ have provided new information about their specific role. Recent information favors a major role for plasmalemma Ca2+ channels in E-C coupling of cardiac muscle, while a major role for sarcoplasmic reticulum Ca2+ release channels (ryanodine receptors) is proposed for E-C coupling of skeletal muscle. In smooth muscle, both plasmalemma and sarcoplasmic reticulum (IP3 receptors) Ca2+ channels are involved in E-C coupling. These studies will be comparatively discussed for skeletal, cardiac and smooth muscle cells.

GTP-dependent regulation of myometrial KCa channels incorporated into lipid bilayers

The regulation of calcium-activated K (KCa) channels by a G protein-mediated mechanism was studied. KCa channels were reconstituted in planar lipid bilayers by fusion of membrane vesicles from rat or pig myometrium. The regulatory process was studied by exploring the actions of GTP and GTP gamma S on single channel activity. KCa channels had a conductance of 260 +/- 6 pS (n = 25, +/- SE, 250/50 mM KCl gradient) and were voltage dependent. The open probability (Po) vs. voltage relationships were well fit by a Boltzmann distribution. The slope factor (11 mV) was insensitive to internal Ca2+. The half activation potential (V1/2) was shifted -70 mV by raising internal Ca2+ from pCa 6.2 to pCa 4. Addition of GTP or GTP gamma S activated channel activity only in the presence of Mg2+, a characteristic typical of G protein-mediated mechanisms. The Po increased from 0.18 +/- 0.08 to 0.49 +/- 0.07 (n = 7, 0 mV, pCa 6 to 6.8). The channel was also activated (Po increased from 0.03 to 0.37) in the presence of AMP-PNP, a nonphosphorylating ATP analogue, suggesting a direct G protein gating of KCa channels. Upon nucleotide activation, mean open time increased by a factor of 2.7 +/- 0.7 and mean closed time decreased by 0.2 +/- 0.07 of their initial values (n = 6). Norepinephrine (NE) or isoproterenol potentiated the GTP-mediated activation of KCa channels (Po increased from 0.17 +/- 0.06 to 0.35 +/- 0.07, n = 10). These results suggest that myometrium possesses beta-adrenergic receptors coupled to a GTP-dependent protein that can directly gate KCa channels. Furthermore, KCa channels, beta-adrenergic receptors, and G proteins can be reconstituted in lipid bilayers as a stable, functionally coupled, molecular complex.

Decreased number of peripheral blood CD4 + CD29+ lymphocytes and increased in vitro spontaneous production of anti-DNA antibodies in patients with active systemic lupus erythematosus

Flow cytometric 2-color analysis of peripheral blood lymphocytes from patients with systemic lupus erythematosus (SLE) showed a reduction of relative and absolute number of CD4+ CD29+ cells compared to matched healthy individuals. This abnormality was more marked in patients with active/very active disease. Absolute number of CD4+ CD29+ cells was negatively correlated with spontaneous anti-DNA Ig production that we demonstrated to be a laboratory index strongly correlated with a clinical disease activity score. A decrease of the percentage of CD8+ CD29+ lymphocytes in patients with active disease was also observed.

Repetitive stimulation increases the activation rate of skeletal muscle Ca2+ currents

Voltage clamp experiments were conducted in frog skeletal muscle using repetitive stimulation protocols. The activation rate of Ca2+ currents increased by prepulses to depolarizing potentials or by stimulating the fiber with a frequency of 1.7 Hz at 0 mV. The effect was observable with Ca2+ or Ba2+ ions, and was clearly voltage-dependent. Physiologically, it is relevant that such activation rate increase can take place during a train of action potentials.

Hormonal regulation of potassium currents in single myometrial cells

Three potassium currents (IK) were recorded from myometrial cells isolated from the uterus of rats at estrus and diestrus and kept in culture for 1-6 days. IK were differentiated by their modulation with norepinephrine and/or by their onset kinetics. At +50 mV the activation time constants were about 0.7 ms, 6 ms, and 15 ms for the fast, the intermediate, and the slow IK, respectively. Norepinephrine (1 microM) potentiated the fast IK and reduced the intermediate IK. In addition, differences were found with respect to cells from animals at estrus and diestrus. The fast IK was preferentially expressed in cultures from animals at estrus, whereas the intermediate IK was more frequent in cells from rats at diestrus. These results indicate that K+ channels from myometrial cells are multiregulated. Regulation may occur by short-term signals (neurotransmitters) and/or by preferentially expressing distinct types of channels depending on the hormonal status of the animal.

ANG II inhibits calcium-activated potassium channels from coronary smooth muscle in lipid bilayers

Angiotensin II (ANG II) is a powerful vasoconstrictor of coronary vessels and other smooth muscles. One of the actions of ANG II is the inhibition of K+ currents, possibly contributing to depolarization and contraction. Therefore, we investigated the role of ANG II on the regulation of K+ channels at the single-channel level. We studied its effect on calcium-activated potassium (KCa) channels (congruent to 250 pS) from coronary smooth muscle incorporated into lipid bilayers. KCa channels were sensitive to externally applied ANG II at voltages from -20 to -70 mV and pCa between 6.5 and 4. The dose-response curve gave a concentration of half-inhibition (Ki1/2) of 58 nM and a Hill coefficient of 2.2, indicating a minimum of two sites in the process. ANG II modified the open and closed states of the channel, affecting their proportions and their values. In addition, a new much slower (congruent to 1 s) closed or "blocked" state appeared. We conclude that one of the mechanisms by which ANG II causes vasoconstriction of the coronary vessels is a direct inhibition of KCa channels contributing to depolarization and contraction.

[The effects of orthodontic treatment on periodontal findings in adults]

After periodontal therapy 12 patients with advanced alveolar bone loss were orthodontically treated and recalled for approximately 51.1 months. Orthodontic tooth movement resulted in a mean overjet reduction of 1.7 mm, a mean overbite reduction of 1.3 mm and closure of the anterior spaces. No significant differences were observed in the probing depths and attachment levels between the test and control teeth. 31% of the treated teeth showed signs of root resorption. The results indicate that orthodontic therapy in patients with successfully treated advanced periodontal disease does not lead to further attachment loss if the patients are periodontally well maintained.

Relationship between myoplasmic calcium transients and calcium currents in frog skeletal muscle

Ca2+ currents (ICa) and myoplasmic Ca2+ transients were simultaneously recorded in single muscle fibers from the semitendinosus muscle of Rana pipiens. The vaseline-gap voltage-clamp technique was used. Ca2+ transients were recorded with the metallochromic indicator dye antipyrylazo III. Ca2+ transients consisted of an early fast rising phase followed by a late slower one. The second phase was increased by experimental maneuvers that enlarged ICa, such as augmenting [Ca2+]o (from 2 to 10 mM) or adding (-)-Bay K 8644 (2 microM). When [Ca2+]o was increased, the second phase of the Ca2+ transients and ICa showed an average increase at 0 mV of 2 +/- 0.9 microM (4) and 1.4 +/- 0.3 mA/ml (4), respectively. (-)-Bay K 8644 increased the late phase of the Ca2+ transients and ICa at 0 mV by 0.8 +/- 0.3 microM (3) and 6.7 +/- 2.0 mA/ml (4), respectively. The initial fast rising phase of the Ca2+ transients was not modified. (-)-Bay K 8644 slowed the time constant of decay of the transients by 57 +/- 6 ms. In other experimental conditions, Ca2+ release from the sarcoplasmic reticulum (SR) was impaired with repetitive stimulation in 1 mM [EGTA]i-containing fibers. Under those circumstances, Ca2+ transients directly followed the time integral of ICa. Pulses to 0 mV caused a large Ca2+ transient that became suppressed when large pulses to 100 mV were applied. In fibers with functioning SR, pulses to 100 mV elicited somewhat smaller or similar amplitude Ca2+ transients when compared with those elicited by pulses to 0 mV. The increase in ICa after raising [Ca2+]o or adding (-)-Bay K 8644 cannot directly explain the change in Ca2+ transients in fibers with functioning SR. On the other hand, when Ca2+ release from the SR is impaired Ca2+ transients depend on ICa.