Calcium release from sarcoplasmic reticulum of normal and dystrophic mice

Contraction of skeletal muscle is triggered by release of calcium from the sarcoplasmic reticulum. In this study, highly purified normal and dystrophic mouse sarcoplasmic reticulum vesicles were compared with respect to calcium release characteristics. Sarcoplasmic reticulum vesicles were actively loaded with calcium in the presence of an ATP-regenerating system. Calcium fluxes were followed by dual wavelength spectrophotometry using the metallochromic indicators antipyrylazo III and arsenazo III, and by isotopic techniques. Calcium release from sarcoplasmic reticulum vesicles was elicited by (a) changing the free calcium concentration of the assay medium (calcium-induced calcium release); (b) addition of a permeant anion to the assay medium, following calcium loading in the presence of a relatively impermeant anion (depolarization-induced calcium release); (c) addition of the lipophilic anion tetraphenylboron (TPB^?) to the assay medium and (d) using specific experimental conditions, i.e. high phosphate levels and low magnesium (spontaneous calcium release). Drugs known to influence Ca²⁺ release were shown to differentially affect the various types of calcium release. Caffeine (10 mM) was found to enhance calcium-induced calcium release from isolated sarcoplasmic reticulum. Ruthenium red (20 μM) inhibited both calcium-induced calcium release and tetraphenylboron-induced calcium release, and partially inhibited spontaneous calcium release and depolarization-induced calcium release. Local anesthetics inhibited spontaneous calcium release in a time-dependent manner, and inhibited calcium-induced calcium release instantaneously, but did not inhibit depolarization-induced calcium release. Use of pharmacological agents indicates that several types of calcium release operate in vitro. No significant differences were found between normal and dystrophic sarcoplasmic reticulum in calcium release kinetics or drug sensitivities.     

Energetics of sodium-dependent α-aminoisobutyric acid transport in the moderate halophile Vibrio costicola

The energetics of α-aminoisobutyric acid transport were examined in Vibrio costicola grown in a medium containing the NaCl content (1 M) optimal for growth. Respiration rate, the membrane potential (Δψ) and α-aminoisobutyric acid transport had similar pH profiles, with optima at 8.5–9.0. Cells specifically required Na⁺ ions to transport α-aminoisobutyric acid and to maintain the highest Δψ (150–160 mV). Sodium was not required to sustain high rates of O₂-uptake. Δψ (and α-aminoisobutyric acid transport) recovered fully upon addition of Na⁺ to Na⁺-deficient cells, showing that Na⁺ is required in formation or maintenance of the transmembrane gradients of ions. Inhibitions by protonophores, monensin, nigericin and respiratory inhibitors revealed a close correlation between the magnitudes of Δψ and α-aminoisobutyric acid transport. Also, dissipation of Δψ with triphenylmethylphosphonium cation abolished α-aminoisobutyric acid transport without affecting respiration greatly. On the other hand, alcohols which stimulated respiration showed corresponding increases in α-aminoisobutyric acid transport, without affecting Δψ. Similarly, N,N′-dicyclohexylcarbodiimide (10 μM) stimulated respiration and α-aminoisobutyric acid transport and did not affect Δψ, but caused a dramatic decline in intracellular ATP content. From these, and results obtained with artificially established energy sources (Δψ and Na⁺ chemical potential), we conclude that Δψ is obligatory for α-aminoisobutyric acid transport, and that for maximum rates of transport an Na⁺ gradient is also required.     

Influence of FeEDDHA and soil temperature on the growth of two soybean varieties

Bulk samples of 30 surface soils characterized in the National Cooperative Soil Survey of Louisiana were collected at the original sites and planted with sorghum-sudangrass in the greenhouse. The native K was exhausted by a total of four croppings. The available soil K was extracted with 1N NH₄OAc 7.0 and 0.1N HCl while the difficultly available-K was extracted by 0.3N NaTPB (sodium tetraphenylboron). In addition, the mica content was estimated by differential dissolution. All soils except Dundee produced the greatest dry matter yield in the first crop with steadily decreasing production in the succeeding crops. The same pattern was shown in the K uptake. It appears that the first crop removed a large portion of the exchangeable K. There was a high degree of relationship between plant uptake of K and exchangeable K in the soils (r²=0.89^**). Uptake by the subsequent crops was generally controlled by the K in the micaceous minerals (r²=0.89^**). Since there was a high coefficient of determination between mica-K and difficulty available-K (r²=0.91^**) one also finds that uptake of K by crops 2, 3 and 4 was also well correlated to difficultly available K (R²=0.94^**). The uptake of K that was not originally in the exchangeable form was also highly related to difficultly available-K (R²=0.51^**). Contribution from the Department of Agronomy, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge. Part of the M.S. theses of the senior authors. Former Graduate Students and Prof. of Agronomy, respectively.