Dietary subacute zinc deficiency and potassium metabolism

In a controlled animal experiment the effects of dietary subacute Zn deficiency on growth, Zn concentration, and tissue 42-K distribution were studied. Growth retardation caused lower body weight because both skeletal and heart muscle showed a reduction in cell mass. Zn concentrations were reduced in most tissues, however, they remained unaltered in heart muscle. 42-K activity increased in skeletal muscle and pancreas. We hypothesize the latter reflects the organs rate of metabolism, inducing the exocrine pancreas to increase Zn absorption; in skeletal muscle it may induce also alterations in cell potentiation, causing restless behavior. As suggested by the calculated specific K activity (Bq/mol), the K uptake was highest in liver and bone, high in pancreas and skeletal muscle and low in heart muscle. The latter suggests K retention in heart muscle. Specific activity in plasma and jejunum remained unaltered: K status and absorption seem unaffected. Zn deficiency causes different 42-K activities in the various tissues, that respond by alterations in K metabolism without the induction of K deficiency.     

Reversible unfolding of fructose 6-phosphate, 2-kinase:fructose 2,6-bisphosphatase.

Reversible unfolding of rat testis fructose 6-phosphate,2-kinase:fructose 2,6-bisphosphatase in guanidine hydrochloride was monitored by following enzyme activities as well as by fluorescence methodologies (intensity, emission maximum, polarization, and quenching), using both intrinsic (tryptophan) and extrinsic (5((2-(iodoacetyl)amino) ethyl)naphthalene-1-sulfonic acid) probes. The unfolding reaction is described minimally as a 4-state transition from folded dimer-->partially unfolded dimer-->monomer-->unfolded monomer. The partially unfolded dimer had a high phosphatase/kinase ratio due to preferential unfolding of the kinase domain. The renaturation reaction proceeded by very rapid conversion (less than 1 s) of unfolded monomer to dimer, devoid of any enzyme activity, followed by slow (over 60 min) formation of the active enzyme. The recovery rates of the kinase and the phosphatase were similar. Thus, the refolding appeared to be a reversal of the unfolding pathway involving different forms of the transient dimeric intermediates. Fluorescence quenching studies using iodide and acrylamide showed that the tryptophans, including Trp-15 in the N-terminal peptide, were only slightly accessible to iodide but were much more accessible to acrylamide. Fructose 6-phosphate, but not ATP or fructose 2,6-bisphosphate, diminished the iodide quenching, but all these ligands inhibited the acrylamide quenching by 25%. These results suggested that the N-terminal peptide (containing a tryptophan) was not exposed on the protein surface and may play an important role in shielding other tryptophans from solvent.     

Guanine nucleotide regulatory protein alterations in young Milan hypertensive strain rats

Vascular smooth muscle cell membranes from prehypertensive rats of the Milan hypertensive strain (MHS) were used to examine adenylyl cyclase activity and its regulation by guanine nucleotide regulatory proteins (G-proteins). Basal adenylyl cyclase activity was similar in MHS and Milan normontensive strain (MNS) membranes. Forsokolin (10^?4 M) produced a significantly greater stimulatory response in MHS membranes, but this was not observed with NaF (10^?2 M). Isoporterenol (10^?4 M) caused a significantly decreased stimulation of adenylyl cyclase activity in MHS membranes, while prostaglandin E₁ (10^?5 M) produced similar responses in the two strains. G_i function and GTP responses, as observed by biphasic effects of GTP on isoproterenol-stimulated membranes, were similar in both strains. The levels of G_i2α and G_qα/G₁₁α were similar in the two strains, while the levels of G_sα (44 and 42 kDa forms) and the β-subunit were significantly reduced by ～20% in MHS membranes. The α-subunit of G_i3 was dramatically reduced by ～80% in MHS membranes. The affinities of β-adrenergic receptors for the antagonist, cyanophindolol, were similar in the two strains; however, the number of β-adrenoceptors was substantially reduced in MHS membranes. These findings may be of relevance to altered vascular reactivity and transmembrane ion distribution observed in the MHS.     

横纹肌肌原纤维的第三肌丝──肌联蛋白

实验研究证明,在动物横纹肌肌原纤维中,除包含有粗肌丝、细肌丝外,还有纤肌丝的存在,肌联蛋白（肌巨蛋白）是具有挠性的线状蛋白质,分子量为3000 000,长度约为0.9μm,跨越肌原纤维的M－线和Z－线,形成纤肌丝.其生理功能是在粗肌丝装配中具有分子模板作用,并将粗肌丝稳定于肌原纤维肌小节中央以及可参与肌球蛋白活性的调节.     

鸣鸣蝉（Oncotympana maculaticollis Motsch）发声肌中肌原纤维的双阵列结构及莫发声原初过程的分析

给出了鸣鸣蝉发声肌肌原纤维的双阵列结构,其肌纤维中并存两种不同阵列的“快”和“慢”动肌原纤维（ＦＳＭ和ＳＳＭ）．ＦＳＭ和ＳＳＭ虽然由粗肌丝构成相同的阵列骨架,但细肌丝对粗肌丝的比例（ＲＴＩＦ）不同,分别为３：１和５：１．明显区别于单音调鸣声的蝉类发声肌肌原纤维的ＲＴＩＦ为３：１的单阵列结构,即与鸣鸣蝉变音调声产生的原初机制相适应．     

Myosin light chain kinase expression during smooth muscle development

The expression of smooth muscle myosin light chain kinase (MLCK) was investigated during chicken gizzard development. The molecular weight and the antigenic properties of MLCK did not change during development. The use of anion exchange high performance liquid chromatography (HPLC) enabled us to distinguish between MLCKs from post-hatched and adult chickens. A partial amino acid sequence determination of 4-day-old gizzard MLCK failed to disclose differences in the primary sequences of the two proteins. The results suggest that MLCK has the same primary sequence in all sequences of the two proteins. The results suggest that MLCK has the same primary sequence in all stages of gizzard development, although charge variants due to post-translational modifications may exist.     

Effects of testosterone on a sexually dimorphic frog muscle: Repeated in vivo observations and androgen receptor distribution

In the present study the sexually dimorphic, androgen-sensitive flexor carpi radialis muscle (FCR) in male Xenopus laevis was viewed repeatedly in vivo to assess the influence of testosterone on muscle fiber size over a period of up to 12 weeks. Regions of the muscle innervated by different spinal nerves responded differently to testosterone treatment. Muscle fibers innervated by spinal nerve 2 (SN2) hypertrophied within 7 days in frogs that had been castrated and given testosterone-filled implants. This initial hypertrophy was followed by a return to normal fiber size a week late, after which fiber size slowly increased again. In castrated males with empty implants, muscle fibers innervated by SN2 gradually atrophied. Fibers innervated by spinal nerve 3 (SN3) were not affected by androgen replacement or withdrawal. The sartorius, a control muscle that is neither sexually dimorphic nor particularly androgen sensitive, was also unaffected. The in vivo observations were confirmed by measurements of muscle fiber cross-sectional areas in frozen sections of whole forelimbs. At 8 and 12 weeks after castration, cross-sectional areas of fibers innervated by SN2 were significantly larger in frogs provided with testosterone than in castrates without testosterone. No difference was found in the SN2 region or in the anconeus caput scapulare (triceps), another control muscle. Immunocytochemistry employing an antibody against the androgen receptor (AR) indicated that the receptor is present in myonuclei of all muscles of the forelimb. While no difference in labeling intensity was detected, the number of AR-containing nuclei per muscle fiber cross-section was higher in fibers innervated by SN2 than in those innervated by SN3, and was yet lower in the triceps. This suggests that regulation of androgen sensitivity may occur via muscle fiber. ARs, although an influence of the nerve may also contribute. 1994 John Wiley & Sons, Inc.     

大黄素对豚鼠结肠带平滑肌细胞电和收缩性能的影响

联合应用平滑肌肌力张力测量技术和细胞内微电极记录技术,同步地现测豚鼠结肠带平滑肌自发的肌源性电活动和力学活动,研究了大黄素的药物作用。大黄素能缩短膜电位的波动周期,从而缩短峰电位集簇发放的周期;相应地,可使平滑肌的分节律收缩加快,幅值指数升高。大黄素又能促使细胞膜电位自发的周期性波动的出现,导致峰电位的集簇发放;相应地,可使强直收缩转化为分节律收缩,即促进收缩形式向有利于肠道推进功能的方向转化。以上结果表明,大黄素能有效地提高豚鼠结肠带平滑肌细胞的电兴奋性和收缩功能,并且对其电学和力学活动的影响之间有明确的对应关系。