Modulation of transient type K channel cloned from rat heart.

We have cloned a transient type K channel from rat heart (RH10) and coexpressed a metabotropic glutamate receptor (mGluR5) to study the functional modulation of RH10 coupled to the phosphatidylinositol (PI) hydrolysis. Stimulation of mGluR5 suppressed peak amplitude of RH10 current and affected voltage dependence of activation and inactivation of the channel.     

Isolation of thymidine-requiring variants from rat nerve-like cells

Thymidine auxotrophs (B3T) of rat nerve-like cells (B103) were isolated. B103 cells were preincubated in a thymidine medium and mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Afterward, cells were incubated in a medium supplemented with dialyzed fetal calf serum and then treated with 5-fluorodeoxyuridine for 24 h. Next, cells were grown in a thymidine medium for twenty days. Thymidine auxothrophs were thus obtained and one clone of them was designated B3T cells. The modal number of chromosomes in B3T cells was 85. Growth tests revealed the following interesting facts: (1) The medium containing pyrazofurin and uridine could not support the growth of B3T cells, but the addition of thymidine to such a medium enabled cells to grow. (2) Even deoxyuridine supported the growth of B3T cells when added to the medium of pyrazofurin and uridine. These findings suggest that the catalytic ability of thymidylate synthetase in B3T cells may have decreased, probably due to the decreased affinity of the enzyme molecules to the substrate (dUMP), and that thymidine kinase activity was high enough to support the growth of B3T cells. B3T cells have maintained the ability to differentiate and extend neurites in response to dibutyryl-cyclic AMP as also demonstrated in wild cells (B103). B3T cells will be available for genetical and molecular biological studies of neuronal cells.     

Effects of ghrelin on neuronal activity in the ventromedial nucleus of the hypothalamus in infantile rats: An in vitro study

Ghrelin is an endogenous ligand for the growth hormone (GH) secretagogue (GHS) receptor (GHS-R) and a potent stimulant for GH secretion even in infantile rats before puberty. Although the ventromedial nucleus of the hypothalamus (VMH) might be a site of action for ghrelin to induce GH release, the electrophysiological effect of ghrelin on VMH neurons in infantile rats remains to be elucidated. Thus, the purpose of the present study was to investigate the effect of ghrelin on VMH neurons using hypothalamic slices of infantile rats. Ghrelin excited a majority of VMH neurons in a concentration-dependent manner. VMH neurons that were excited by GH releasing peptide-6 (GHRP-6), a synthetic GHS, were also excited by ghrelin and vice versa. Repeated application of ghrelin to the same VMH neuron decreased progressively the excitatory responses depending on the number of times it was administered. The excitatory effect of ghrelin on VMH neurons in normal artificial cerebrospinal fluid (ACSF) persisted in low Ca²⁺-high Mg²⁺ ACSF. The present results indicate that (1) ghrelin excites a majority of VMH neurons dose-dependently and postsynaptically and (2) the excitatory effects of ghrelin are mimicked by GHRP-6 and desensitized by repeated applications of ghrelin.     

Sequential polypeptides: 5. Statistical mechanical analysis of helix-coil transition in sequential polypeptides

A statistical mechanical theory of the helix-coil transition in sequential polypeptides is developed assuming that the statistical weights of the Zimm-Bragg parameters of a given residue depend on the type of adjacent residues. In the case of a sequential polypeptide consisting of two kinds of residues, the theory describes the helix- coil transition of the polypeptide in terms of the Zimm-Bragg parameters associated with the corresponding residues. The theory is then used to determine this parameter, as a function of temperature, from experimental data for transition temperature as a function of solvent composition, for a series of sequential polypeptides consisting of Glu(OBzl) and Lys(Chz) residues in mixtures of dichloroacetic acid and 1,2-dichlorethane. This parameter is then combined with the Zimm-Bragg parameters for the parent homopolypeptides, and the theory used to predict helix coil transition curves which are in good agreement with the experimental ones for the sequential polypeptides studied.     

Adaptive Shifts in the Regulation System of Seed Yield in Japanese Species of Epimedium (Berberidaceae)

Abstract Total seed yield per plant in one season was differentiated neither between Epimedium diphyllum and the E. grandiflorum complex ( E. grandiflorum and E. sempervirens ), nor between these two groups and one of their hybrid derived species, E. trifoliatobinatum . Total ovules per plant and seed-set rate per capsule ( SR ) did not vary greatly between these species, and seed weight ( SW ) was almost the same between them. The number of flowers per inflorescence ( F ) was also constant. However, the remaining reproductive component characters, ovule number per ovary ( O ) and inflorescence number per plant ( I ), were differentiated between the three taxa. These two characters were negatively correlated and a trade-off relationship occurred under the constant total seed yield (= O × F × I × SR × SW ). Ovule number per ovary was highly correlated with spur length of the flower. During the course of the hybrid speciation of E. trifoliatobinatum , selection pressure by pollinators on intermediate spur length seems to have favored plants with an intermediate ovule number. On the other hand, this selection pressure counteracted the increase of the inflorescence number under the trade-off. The resultant seed yield of E. trifoliatobinatum did not differ from that of the parental species, but the pattern of ovule allocation to ovaries (capsules) was altered.     

Carbachol and KCl-induced changes in intracellular free calcium concentration in isolated, fura-2 loaded smooth-muscle cells from the anterior byssus retractor muscle of Mytilus edulis

Intracellular free calcium concentration [( Ca2+]1) was measured in suspensions of fura-2 loaded smooth-muscle cells isolated from the anterior byssus retractor muscle of Mytilus edulis. Successive application of 5mM carbachol (CCh) and 100mM KCl to the cells transiently elevated [Ca2+]1 from the resting value of 124 +/- 4.5nM (mean +/- S.E., n = 14) to 295 +/- 15.3 and 383 +/- 20.5 nM, respectively. The response to CCh was concentration-dependent with an ED50 of 10(-5) M. Under the microscope, 67 +/- 3.0 and 83 +/- 1.3 % of fura-2 loaded cells contracted on the addition of 5mM CCh and 100mM KCl, respectively. In Ca2+ -free sea water, the CCh induced change in [Ca2+]1 was partially suppressed whereas that induced by KCl was completely abolished, suggesting an agonist-evoked release of stored Ca2+.     

Physiological role of peroxisomal beta-oxidation in liver of fasted rats

In the livers of fasted rats, the activity of peroxisomal palmitocyl-CoA oxidation (NADH production) was increased more rapidly and markedly than that of mitochondrial carnitine palmitoyltransferase, which is the rate limiting enzyme of mitochondrial beta-oxidation. The peroxisomal oxidizing activity was about twice that of the control throughout the period of fasting (1-7 days). carnitine acetyltransferase activity was increased to a similar extent in both peroxisomes and mitochondria. A possible physiological role of liver peroxisomes may thus be as an effective supply of NADH2, acetyl residues and short and medium-length fatty acyl-CoA in the cells on the enhancement of peroxisomal beta-oxidation of the animals under starvation; these substances thus produced may be transported into the mitochondria as energy sources.