Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

Molecular evolution of voltage-sensitive ion channel genes: on the origins of electrical excitability

We have analyzed nucleic acid and amino acid sequence alignments of a variety of voltage-sensitive ion channels, using several methods for phylogenetic tree reconstruction. Ancient duplications within this family gave rise to three distantly related groups, one consisting of the Na+ and Ca++ channels, another the K+ channels, and a third including the cyclic nucleotide-binding channels. A series of gene duplications produced at least seven mammalian homologues of the Drosophila Shaker K+ channel; clones of only three of these genes are available from all three mammalian species examined (mouse, rat, and human), pointing to specific genes that have yet to be recovered in one or another of these species. The Shaw-related K+ channels and the Na+ channel family have also undergone considerable expansion in mammals, relative to flies. These expansions presumably reflect the needs of the high degree of physiological and neuronal complexity of mammals. Analysis of the separate domains of the four-domain channels (Ca++ and Na+) supports their having evolved by two sequential gene duplications and implies the historical existence of a functional two-domain channel.      

Intensified Tuberculosis Case Finding among Malnourished Children in Nutritional Rehabilitation Centres of Karnataka,India: Missed Opportunities

Background

Severe acute malnutrition (SAM) is the most serious form of malnutrition affecting children under-five and is associated with many infectious diseases including Tuberculosis (TB). In India, nutritional rehabilitation centres (NRCs) have been recently established for the management of SAM including TB. The National TB Programme (NTP) in India has introduced a revised algorithm for diagnosing paediatric TB. We aimed to examine whether NRCs adhered to these guidelines in diagnosing TB among SAM children.

Methods

A cross-sectional study involving review of records of all SAM children identified by health workers during 2012 in six tehsils (sub-districts) with NRCs (population: 1.8 million) of Karnataka, India.

Results

Of 1927 identified SAM children, 1632 (85%) reached NRCs. Of them, 1173 (72%) were evaluated for TB and 19(2%) were diagnosed as TB. Of 1173, diagnostic algorithm was followed in 460 (37%). Among remaining 763 not evaluated as per algorithm, tuberculin skin test alone was conducted in 307 (41%), chest radiography alone in 99 (13%) and no investigations in 337 (45%). The yield of TB was higher among children evaluated as per algorithm (4%) as compared to those who were not (0.3%) (OR: 15.3 [95%CI: 3.5-66.3]). Several operational challenges including non-availability of a full-time paediatrician, non-functioning X-ray machine due to frequent power cuts, use of tuberculin with suboptimal strength and difficulties in adhering to a complex diagnostic algorithm were observed.

Conclusion

This study showed that TB screening in NRCs was sub-optimal in Karnataka. Some children did not reach the NRC, while many of those who did were either not or sub-optimally evaluated for TB. This study pointed to a number of operational issues that need to be addressed if this collaborative strategy is to identify more TB cases amongst malnourished children in India.     

The metabolic significance of pentose cycle measurements in perfused liver

The controversial dissension concerning the nature of the pentose cycle in liver is investigated. The metabolism of [2-14C]Glc and [1-14C]Rib in chronically perfused normal and regenerating rabbit liver and acutely perfused rat liver are used to test the mechanistic predictions and contribution of the F-type pentose cycle. 14C was traced in Glc, Glc 6-P, Fru 6-P, glycogen and Rib 5-P. None of the data complied with the critical theoretical limits set for the C-1/C-3 ratio (the identity badge of the F-type pentose cycle or pathway) for all values of F-type PC from 0-100%. Thus apparent F-type PC measurements using the Katz & Wood method gave a wide scatter of calculated values. The 14C distributions in Rib 5-P do not conform with the predictions of the F-type PC but are in agreement with the many previous results of similar experiments reported by Hiatt and co-workers. In perfused rat liver the C-1/C-3 constants in Glc 6-P and glycogen also failed to conform with F-PC theory following the metabolism of [2-14C]Glc. The metabolism of [5-14C]Glc and distribution of 14C in Glc 6-P and glycogen showed that L-type PC was 18%, in close agreement with a previous published value of 22% for rat hepatocytes. Metabolism of [6-14C]Glc and [4-14C]Glc (as [4,5,6-14C]Glc) showed that Pyruvate Recycling was active in perfused rat liver. None of the data from these comprehensive investigations can confirm the results of the recent study reported by the Landau laboratory on the pentose pathway metabolism of Glc and Rib in perfused rat liver.     

A system for the study in situ of the pentose phosphate pathway in rabbit liver

A surgical procedure for the isolation of the liver from the systemic circulation of the anaesthetized rabbit is described. The technique allowed the metabolism in situ of intraportally infused substrates to be followed for periods up to 5min, free from the contaminating influences of metabolism by other body tissues. Details of the procedures necessary to achieve the uniform infusion, homogeneous distribution and containment of (14)C-labelled glucose substrates in the liver by haemostasis are described. Changes in pO(2), pCO(2), pH and the concentrations of NADP(+), NADPH and glucose during each minute interval of the total 5min period of metabolism are given. Reactant ratios of the lactate dehydrogenase system and the adenine nucleotide system have been calculated from the concentrations of the pertinent metabolites for the same period of metabolism. Glucose production by rabbit liver in situ proceeded at the rate of 1.08mumol/min per g wet wt. of liver during the 5min metabolic interval. The presence of the oxidative reactions of the pentose phosphate pathway of glucose metabolism was inferred from the quotient oxidation of [1-(14)C]glucose/oxidation of [6-(14)C]glucose=1.8.