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Intensive cooling technology is widely used to produce high strength strip steel,but high cooling rate leads to some defects,such as shape waves caused by high residual stress. A numerical model was established to achieve a coupling calculation of temperature,phase transformation and stress for high strength steel(700 MPa) during intensive cooling. Commercial FEM software ABAQUS was used to build coupled models that verified by a series of experiments. The effects of edge masking and initial temperature difference on the residual stress were studied by modifying initial and boundary conditions. It is concluded that reducing the initial temperature difference is more effective to release the residual stress of strip steel during cooling. Proven by industrial experiments,these research results would be used to lower the residual stress and improve the quality of hot-rolled strips.

The tremorogenic fungal metabolite, paxilline, is widely used as a potent and relatively specific blocker of [Ca.sup.2+] -and voltage-activated Slol (or BK) [K.sup.+] channels. The pH-regulated Slo3 [K.sup.+] channel, a Slol homologue, is resistant to blockade by paxilline. Taking advantage of the marked differences in paxilline sensitivity and the homology between subunits, we have examined the paxilline sensitivity of a set of chimeric Slol/Slo3 subunits. Paxilline sensitivity is associated with elements of the S5-P loop-S6 module of the Slol channel. Replacement of the Slol S5 segment or the second half of the P loop results in modest changes in paxilline sensitivity. Replacing the Slol S6 segment with the Slo3 sequence abolishes paxilline sensitivity. An increase in paxilline affinity and changes in block kinetics also result from replacing the first part of the Slol P loop, the so-called turret, with Slo3 sequence. The Slol and Slo3 S6 segments differ at 10 residues. Slol-G311S was found to markedly reduce paxilline block. In constructs with a Slo3 $6 segment, S300G restored paxilline block, but most effectively when paired with a Slol P loop. Other $6 residues differing between Slol and Slo3 had little influence on paxilline block. The involvement of Slol G311 in paxilline sensitivity suggests that paxilline may occupy a position within the central cavity or access its blocking position through the central cavity. To explain the differences in paxilline sensitivity between Slol and Slo3, we propose that the G311/S300 position in Slol and Slo3 underlies a structural difference between subunits in the bend of S6, which influences the occupancy by paxilline. doi/ 10.1085/jgp.201010403

N termini of auxiliary [beta] subunits that produce inactivation of large-conductance [Ca.sup.2+]-activated [K.sup.+] (BK) channels reach their pore-blocking position by first passing through side portals into an antechamber separating the BK pore module and the large C-terminal cytosolic domain. Previous work indicated that the [beta]2 subunit inactivation domain is protected from digestion by trypsin when bound in the inactivated conformation. Other results suggest that, even when channels are closed, an inactivation domain can also be protected from digestion by trypsin when bound within the antechamber. Here, we provide additional tests of this model and examine its applicability to other [beta] subunit N termini. First, we show that specific mutations in the [beta]2 inactivation segment can speed up digestion by trypsin under closed-channel conditions, supporting the idea that the [beta]2 N terminus is protected by binding within the antechamber. Second, we show that cytosolic channel blockers distinguish between protection mediated by inactivation and protection under closed-channel conditions, implicating two distinct sites of protection. Together, these results confirm the idea that [beta]2 N termini can occupy the BK channel antechamber by interaction at some site distinct from the BK central cavity. In contrast, the [beta]3a N terminus is digested over 10-fold more quickly than the [beta]2 N terminus. Analysis of factors that contribute to differences in digestion rates suggests that binding of an N terminus within the antechamber constrains the trypsin accessibility of digestible basic residues, even when such residues are positioned outside the antechamber. Our analysis indicates that up to two N termini may simultaneously be protected from digestion. These results indicate that inactivation domains have sites of binding in addition to those directly involved in inactivation.

The KCNMB3 gene encodes one of a family of four auxiliary [beta] subunits found in the mammalian genome that associate with Slol [alpha] subunits and regulate BK channel function. In humans, the KCNMB3 gene contains four N-terminal alternative exons that produce four functionally distinct [beta]3 subunits, [beta]3a-d. Three variants, [beta]3a-c, exhibit kinetically distinct inactivation behaviors. Since investigation of the physiological roles of BK auxiliary subunits will depend on studies in rodents, here we have determined the identity and functional properties of mouse [beta]3 variants. Whereas [beta]1, [beta]2, and [beta]4 subunits exhibit 83.2%, 95.3%, and 93.8% identity between mouse and human, the mouse [beta]3 subunit, excluding N-terminal splice variants, shares only 62.8% amino acid identity with its human counterpart. Based on an examination of the mouse genome and screening of mouse cDNA libraries, here we have identified only two N-terminal candidates, [beta]3a and [beta]3b, of the four found in humans. Both human and mouse [beta]3a subunits produce a characteristic use-dependent inactivation. Surprisingly, whereas the h[beta]3b exhibits rapid inactivation, the putative m[beta]3b does not inactivate. Furthermore, unlike h[beta]3, the m[beta]3 subunit, irrespective of the N terminus, mediates a shift in gating to more negative potentials at a given [Ca.sup.2+] concentration. The shift in gating gradually is lost following patch excision, suggesting that the gating shift involves some regulatory process dependent on the cytosolic milieu. Examination of additional genomes to assess conservation among splice variants suggests that the putative m[beta]3b N terminus may not be a true orthologue of the h[beta]3b N terminus and that both [beta]3c and [beta]3d appear likely to be primate-specific N-terminal variants. These results have three key implications: first, functional properties of homologous [beta]3 subunits may differ among mammalian species; second, the specific physiological roles of homologous [beta]3 subunits may differ among mammalian species; and, third, some [beta]3 variants may be primate-specific ion channel subunits.

Here we have examined the voltage and pH dependence of unitary Slo3 channels and used analysis of current variance to define Slo3 unitary current properties over a broader range of voltages. Despite complexity in Slo3 channel openings that precludes simple definition of the unitary conductance, average current through single Slo3 channels varies linearly with voltage at positive activation potentials. Furthermore, the average Slo3 unitary current at a given activation potential does not change with pH. Consistent with macroscopic conductance estimates, the apparent open probability of Slo3 channel exhibits a pH-dependent maximum, with limiting values around 0.3 at the most elevated pH and voltage. Estimates of Slo3 conductance at negative potentials support a weaker intrinsic voltage dependence of gating than is observed for Slo1. For the pH-regulated Slo3 [K.sup.+] channel, the dependence of macroscopic conductance on pH suggests that the pH-sensitive mechanism regulates gating in an allosteric manner qualitatively similar to regulation of Slo1 by [Ca.sup.2+]. Together, the results support the view that the regulation of macroscopic Slo3 currents by pH reflects regulation of gating equilibria, and not a direct effect of pH on ion permeation. Specifically, both voltage and pH regulate a closed--open conformational change in a largely independent fashion.

Proteins arising from the Slo family assemble into homotetramers to form functional large-conductance, [Ca.sup.2+-] and voltage-activated [K.sup.+] channels, or BK channels. These channels are also found in association with accessory [beta] subunits, which modulate several aspects of channel gating and expression. Coexpression with either of two such subunits, [beta]2 or [beta]3b, confers time-dependent inactivation onto BK currents, mSlol +[beta]3b channels display inactivation that is very rapid but incomplete. Previous studies involving macroscopic recordings from these channels have argued for the existence of a second, short-lived conducting state in rapid equilibrium with the nonconducting, inactivated conformation. This state has been termed 'pre-inactivated,' or O *. [beta]2-mediated inactivation, in contrast, occurs more slowly but is virtually complete at steady state. Here we demonstrate, using both macroscopic and single channel current recordings, that a preinactivated state is also a property of mSlol + [beta]2 channels. Detection of this state is enhanced by a mutation (W4E) within the initial [beta]2 N[H.sub.2]-terminal segment critical for inactivation. This mutation increases the rate of recovery to the preinactivated open state, yielding macroscopic inactivation properties qualitatively more similar to those of [beta]3b. Furthermore, short-lived openings corresponding to entry into the preinactivated state can be observed directly with single-channel recording. By examining the initial openings after depolarization of a channel containing [beta]2-W4E, we show that channels can arrive directly at the preinactivated state without passing through the usual long-lived open conformation. This final result suggests that channel opening and inactivation are at least partly separable in this channel. Mechanistically, the preinactivated and inactivated conformations may correspond to binding of the [beta] subunit N[H.sub.2] terminus in the vicinity of the cytoplasmic pore mouth, followed by definitive movement of the N[H.sub.2] terminus into a position of occlusion within the ion-conducting pathway.

Mutational analyses have suggested that BK channels are regulated by three distinct divalent cation-dependent regulatory mechanisms arising from the cytosolic COOH terminus of the pore-forming [alpha] subunit. Two mechanisms account for physiological regulation of BK channels by [micro]M [Ca.sup.2+]. The third may mediate physiological regulation by mM [Mg.sup.2+]. Mutation of five aspartate residues (5D5N) within the so-called [Ca.sup.2+] bowl removes a portion of a higher affinity [Ca.sup.2+] dependence, while mutation of D362A/D367A in the first RCK domain also removes some higher affinity [Ca.sup.2+] dependence. Together, 5D5N and D362A/D367A remove all effects of [Ca.sup.2+] up through 1 mM while E399A removes a portion of low affinity regulation by [Ca.sup.2+]/[Mg.sup.2+]. If each proposed regulatory effect involves a distinct divalent cation binding site, the divalent cation selectivity of the actual site that defines each mechanism might differ. By examination of the ability of various divalent cations to activate currents in constructs with mutationally altered regulatory mechanisms, here we show that each putative regulatory mechanism exhibits a unique sensitivity to divalent cations. Regulation mediated by the [Ca.sup.2+] bowl can be activated by [Ca.sup.2+] and [Sr.sup.2+], while regulation defined by D362/D367 can be activated by [Ca.sup.2+], [Sr.sup.2+], and [Cd.sup.2+] . [Mn.sup.2+], [Co.sup.2+], and [Ni.sup.2+] produce little observable effect through the high affinity regulatory mechanisms, while all six divalent cations enhance activation through the low affinity mechanism defined by residue E399. Furthermore, each type of mutation affects kinetic properties of BK channels in distinct ways. The [Ca.sup.2+] bowl mainly accelerates activation of BK channels at low [Ca.sup.2+], while the D362/D367-related high affinity site influences both activation and deactivation over the range of 10-300 [micro]M [Ca.sup.2+]. The major kinetic effect of the E399-related low affinity mechanism is to slow deactivation at mM [Mg.sup.2+] or [Ca.sup.2+]. The results support the view that three distinct divalent-cation binding sites mediate regulation of BK channels. KEY WORDS: BK channels * [Ca.sup.2+] regulatory sites * divalent cations * Slo * activation

An auxiliary [beta]2 subunit, when coexpressed with Slo [alpha] subunits, produces inactivation of the resulting large-conductance, [Ca.sup.2+] and voltage-dependent [K.sup.+] (BK-type) channels. Inactivation is mediated by the cytosolic N[H.sub.2] terminus of the [beta]2 subunit. To understand the structural requirements for inactivation, we have done a mutational analysis of the role of the N[H.sub.2] terminus in the inactivation process. The [beta]2 N[H.sub.2] terminus contains 46 residues thought to be cytosolic to the first transmembrane segment (TM1). Here, we address two issues. First, we define the key segment of residues that mediates inactivation. Second, we examine the role of the linker between the inactivation segment and TM1. The results show that the critical determinant for inactivation is an initial segment of three amino acids (residues 2-4: FIW) after the initiation methionine. Deletions that scan positions from residue 5 through residue 36 alter inactivation, but do not abolish it. In contrast, deletion of FIW or combinations of point mutations within the FIW triplet abolish inactivation. Mutational analysis of the three initial residues argues that inactivation does not result from a well-defined structure formed by this epitope. Inactivation may be better explained by linear entry of the N[H.sub.2]-terminal peptide segment into the permeation pathway with residue hydrophobicity and size influencing the onset and recovery from inactivation. Examination of the ability of artificial, polymeric linkers to support inactivation suggests that a variety of amino acid sequences can serve as adequate linkers as long as they contain a minimum of 12 residues between the first transmembrane segment and the FIW triplet. Thus, neither a specific distribution of charge on the linker nor a specific structure in the linker is required to support the inactivation process. KEY WORDS: inactivation mechanisms * inactivation domains * [K.sup.+] channels' BK channels * [Ca.sup.2+]- and voltagegated [K.sup.+] channels

Author(s): Xiao-Ming Xia; Xuhui Zeng; Christopher J. Lingle (corresponding author) Large conductance, Ca[sup.2+] - and voltage-activated K[sup.+] channels (BK) respond to two distinct physiological signals--membrane voltage and cytosolic Ca[sup.2+] (refs [...]

Transverse bending, a common shape defect of hot-rolled strips, is generally controlled based on experience, which lacks quantitative study. This leads to some production problems such as difficult feeding and surface scratching in subsequent processes. Based on the principle of elastic mechanics, the mechanism of transverse bending in the process of uncoiling is studied and an analytical model is established. Then the relationship between transverse bending and influence factors, including the curvature radius of longitudinal bending, strip width and strip thickness, is obtained. The study indicates that the transverse bending is caused by longitudinal bending before uncoiling. And the strip width and the curvature radius of longitudinal bending have a great influence on the transverse bending but the strip thickness has little influence. The transverse bending diminishes nonlinearly with the increase of curvature radius of longitudinal bending and increases nonlinearly with the increase of strip width. [ABSTRACT FROM AUTHOR]

A family of auxiliary [Beta] subunits coassemble with Slo [Alpha] subunit to form [Ca.sup.2+] -regulated, voltage-activated BK-type [K.sup.+] channels. The [Beta] subunits play an important role in regulating the functional properties of the resulting channel protein, including apparent [Ca.sup.2+] dependence and inactivation. The [Beta]3b auxiliary subunit, when coexpressed with the Slo [Alpha] subunit, results in a particularly rapid (~1 ms), but incomplete inactivation, mediated by the cytosolic [NH.sub.2] terminus of the [Beta]3b subunit (Xia et al., 2000). Here, we evaluate whether a simple block of the open channel by the [NH.sub.2]-terminal domain accounts for the inactivation mechanism. Analysis of the onset of block, recovery from block, time-dependent changes in the shape of instantaneous current-voltage curves, and properties of deactivation tails suggest that a simple, one step blocking reaction is insufficient to explain the observed currents. Rather, blockade can be largely accounted for by a two-step blocking mechanism [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] in which preblocked open states ([O*.sub.n]) precede blocked states ([I.sub.n]). The transitions between O* and I are exceedingly rapid accounting for an almost instantaneous block or unblock of open channels observed with changes in potential. However, the macroscopic current relaxations are determined primarily by slower transitions between O and O*. We propose that the O to O* transition corresponds to binding of the [NH.sub.2]-terminal inactivation domain to a receptor site. Blockade of current subsequently reflects either additional movement of the [NH.sub.2]-terminal domain into a position that hinders ion permeation or a gating transition to a closed state induced by binding of the [NH.sub.2] terminus. KEY WORDS: channel block * [K.sup.+] channels * gating mechanisms * [Ca.sup.2+]- and voltage-gated [K.sup.+] channels * mSlo channels *

Both [Beta]1 and [Beta]2 auxiliary subunits of the BK-type [K.sup.+] channel family profoundly regulate the apparent [Ca.sup.2+] sensitivity of BK-type [Ca.sup.2+]-activated [K.sup.+] channels. Each produces a pronounced leftward shift in the voltage of half-activation ([V.sub.0.5]) at a given [Ca.sup.2+] concentration, particularly at [Ca.sup.2+] above 1 [micro]M. In contrast, the rapidly inactivating [Beta]3b auxiliary produces a leftward shift in activation at [Ca.sup.2+] below 1 [micro]M. In the companion work (Lingle, C.J., X.-H. Zeng, J.-P. Ding, and X.-M. Xia. 2001. J. Gen. Physiol. 117:583-605, this issue), we have shown that some of the apparent [Beta]3b-mediated shift in activation at low [Ca.sup.2+] arises from rapid unblocking of inactivated channels, unlike the actions of the [Beta]1 and [Beta]2 subunits. Here, we compare effects of the [Beta]3b subunit that arise from inactivation, per se, versus those that may arise from other functional effects of the subunit. In particular, we examine gating properties of the [Beta]3b subunit and compare it to [Beta]3b constructs lacking either the [NH.sub.2-] or COOH terminus or both. The results demonstrate that, although the [NH.sub.2] terminus appears to be the primary determinant of the [Beta]3b-mediated shift in [V.sub.0.5] at low [Ca.sup.2+], removal of the [NH.sub.2] terminus reveals two other interesting aspects of the action of the [Beta]3b subunit. First, the conductance-voltage curves for activation of channels containing the [Beta]3b subunit are best described by a double Boltzmann shape, which is proposed to arise from two independent voltage-dependent activation steps. Second, the presence of the [Beta]3b subunit results in channels that exhibit an anomalous instantaneous outward current rectification that is correlated with a voltage dependence in the time-averaged single-channel current. The two effects appear to be unrelated, but indicative of the variety of ways that interactions between [Beta] and [Alpha] subunits can affect BK channel function. The COOH terminus of the [Beta]3b subunit produces no discernible functional effects. KEY WORDS: [K.sup.+] channels * [Ca.sup.2+]-and voltage-gated [K.sup.+] channels * mSlo channels * voltage-dependent gating * inactivation