Hypertension,calcium channel and pyridoxine (vitamin B6)

The moderately pyridoxine (vitamin B₆)-deficient male rat was introduced by us as an animal model (B6DHT) for the study of hypertension. Hypertension in this rat is associated with increased sympathetic stimulation. Arterial segments from B6DHT rats maintained a higher resting tone. The influx of ⁴⁵calcium into intracellular compartment of the vascular smooth muscle of the caudate artery of B6DHT rats was also enhanced. Administration of pyridoxine attenuated the hypertension in B6DHT rats as well as in genetic or dietary-induced moderately hypertensive conditions such as in the Zucker obese rat and sucrose or low calcium-fed rats. However, pyridoxine did not have any effect or the spontaneously hypertensive rat. All classes of calcium channel blockers were effective in lowering the systolic blood pressure of B6DHT rats. The increased in vitro influx of⁴⁵ calcium into intracellular compartment of artery segments of B6DHT rats as well as the BAY K 8644-induced influx of⁴⁵ calcium into artery segments from normal rats were blocked by pyridoxal phosphate as well as by dihydropyridine-sensitive calcium channel blockers (DHP). Pyridoxal phosphate (PLP) in vitro enhances the binding of calcium channel antagonists to membrane preparations from vascular tissue. PLP corrects the membrane abnormality in responsive hypertensive conditions and thus, could be an endogenous modulator of DHP - sensitive calcium channels.     

Studies on metabolism of vitamin A. The effect of vitamin A status on the secretion rates of some steroids into the ovarianvenous blood of pregnant rats

1. Rats raised on a vitamin A-deficient diet supplemented with either retinyl acetate or retinoic acid were mated and became pregnant. 2. The rates of secretion of progesterone, 20alpha-hydroxypregn-4-en-3-one, oestradiol-17beta and oestrone into the ovarian-venous blood of rats in these two groups were measured on days 9 and 15 of pregnancy. 3. Rates of secretion of progesterone and 20alpha-hydroxypregn-4-en-3-one, both on days 9 and 15, were lower for the rats given retinoic acid. No such differences were found in ovarian oestrogen secretion. 4. The implications of these results are discussed in the light of the previous demonstration that the activity of ovarian 3beta-hydroxy-Delta(5)-steroid dehydrogenase was markedly less in pregnant rats given retinoic acid.     

Pathways of absorption of retinal and retinoic acid in the rat

The chemical and anatomical pathways of absorption of dietary retinal, retinoic acid, and retinol were examined in rats containing lymph, bile, and duodenal cannulae. The experiments were designed to maintain physiological conditions to the greatest possible extent. In each rat an uninterrupted flow of bile into the duodenum was maintained by connecting the duodenal cannula to the bile duct of a second rat. Labeled vitamin A compounds were introduced into the duodenum in very small amounts (7-14 micrograms) in the form of a bile-lipid mixture resembling normal intestinal contents. Under these conditions, most (70-80%) of the radioactivity recovered after the feeding of labeled retinol or retinal was found in the lymph, predominantly in saturated retinyl esters. In contrast, 92-95% of the radioactivity recovered after the feeding of labeled retinoic acid was found in the bile, and was contained in a mixture of polar metabolites, most of them more polar than free retinoic acid. Two-thirds of the small amount of radioactivity found in lymph after retinoic acid-(14)C feeding was in the form of free retinoic acid. The results indicate that under normal conditions the major pathway of retinal absorption involves its reduction to retinol, which is then esterified and transported via the lymphatics in a manner similar to that of dietary retinol. A small proportion of retinal is apparently normally oxidized, and is then transported via the portal vein and excreted in the bile in a manner similar to that of dietary retinoic acid. The relative importance, in quantitative terms, of these two pathways of retinal metabolism can vary, depending on the status of the animal.     

Calcium-dependent protein kinase 29 modulates PIN-FORMED polarity and Arabidopsis development via its own phosphorylation code

PIN-FORMED (PIN)-mediated polar auxin transport (PAT) is involved in key developmental processes in plants. Various internal and external cues influence plant development via the modulation of intracellular PIN polarity and, thus, the direction of PAT, but the mechanisms underlying these processes remain largely unknown. PIN proteins harbor a hydrophilic loop (HL) that has important regulatory functions; here, we used the HL as bait in protein pulldown screening for modulators of intracellular PIN trafficking in Arabidopsis thaliana. Calcium-dependent protein kinase 29 (CPK29), a Ca²⁺-dependent protein kinase, was identified and shown to phosphorylate specific target residues on the PIN-HL that were not phosphorylated by other kinases. Furthermore, loss of CPK29 or mutations of the phospho-target residues in PIN-HLs significantly compromised intracellular PIN trafficking and polarity, causing defects in PIN-mediated auxin redistribution and biological processes such as lateral root formation, root twisting, hypocotyl gravitropism, phyllotaxis, and reproductive development. These findings indicate that CPK29 directly interprets Ca²⁺ signals from internal and external triggers, resulting in the modulation of PIN trafficking and auxin responses.

Ca²⁺-dependent protein kinase 29 directly phosphorylates the hydrophilic loop of PIN-FORMED proteins to modulate their intracellular trafficking and Arabidopsis development.     

Size-spectra as indicators of the effects of fishing on coral reef fish assemblages

The data requirements and resources needed to develop multispecies indicators of fishing impacts are often lacking and this is particularly true for coral reef fisheries. Size-spectra, relationships between abundance and body-size class, regardless of taxonomy, can be calculated from simple sizeabundance data. Both the slope and the mid-point height of the relationship can be compared at different fishing intensities. Here, we develop size-spectra for reef fish assemblages using body size- abundance data collected by underwater visual census in each of ten fishing grounds across a known gradient of fishing intensity in the Kadavu Island group, Fiji. Slopes of the size-spectra became steeper (F_9,69=3.20, p<0.01) and the height declined (F_9,69=15.78, p<0.001) with increasing fishing intensity. Regressions of numbers of individuals per size class across grounds were negative for all size classes, although the slope was almost zero for the smallest size class. Response to exploitation of each size class category was greatest for larger fish. Steepening of the slope with increasing fishing intensity largely resulted from reductions in the relative abundance of large fish and not from the ecological release of small fish following depletion of their predators. The slope and height of the size-spectrum appear to be good indicators of fishing effects on reef fish assemblages.