The presence and binding characteristics of calmodulin in microsomal preparations enriched in sarcoplasmic reticulum from rabbit skeletal muscle

ATP-dependent oxalate facilitated calcium transport in sarcoplasmic reticulum (SR) preparations obtained from rabbit vastus lateralis muscle (fast skeletal muscle; F_sr) and soleus (slow skeletal muscle; S_sr) was determined. Addition of exogenous calmodulin did not stimulate calcium transport in either F_sr or S_sr preparations. F_sr and S_sr previously washed in 1 mM EGTA demonstrated a reduced capacity to transport Ca²⁺; the exogenous addition of calmodulin (0.24 μM) under these conditions, did not restore uptake activity but significantly decreased the steady-state level of Ca²⁺ uptake. Extracts of skeletal SR prepared by treatment with 0.2 mM EDTA and boiling produced significantly more stimulation of red cell Ca²⁺ATPase activity than extracts prepared by boiling alone. This stimulation of red cell Ca²⁺-ATPase was inhibited to a significant extent by $\text{48}\text{80}$, a known anti-calmodulin agent. Radioimmunoassay revealed that extracts prepared by boiling or EDTA-treatment followed by boiling contained considerable amounts of calmodulin. Washing with 1 mM EGTA, though, did not release any calmodulin from SR. These studies reveal that calmodulin is present in both F_sr and S_sr and can only be removed by harsh treatments. The role of calmodulin in skeletal muscle Ca²⁺-transport remains to be determined.     

Volume regulation in salt-acclimated toad (Bufo viridis): the role of urea and the urinary bladder

Body water (weight) was studied in the euryhaline toad Bufo viridis during high salt (500 mOsm NaCl) acclimation. Plasma osmolality was greatly increased upon salt acclimation mainly by urea, and was always hyperosmotic to the ambient solution. Water content was regulated quite efficiently in slowly acclimated undisturbed toads. Repeatedly catheterized toads behaved like osmometers when transferred to hyperosmotic solutions. Total urea loss was greatly reduced in salt acclimated toads, suggesting urine was not voided under these conditions. It is concluded that urea accumulation, inhibition of the urine voiding response and the urine in the bladder are the principal factors involved in volume regulation under conditions of salt acclimation.     

Evaluation of the Escherichia coli K12 inductest for detection of potential chemical carcinogens

46 chemicals of diverse classes and structures, including 30 known animal carcinogens, were evaluated for prophage-inducing ability using the Escherichia coli inductest with lysogenic strain GY5027 envA - uvrB- and indicator strain GY4015 ampR . The inductest detected 9 of 30 known carcinogens as genotoxic agents, including 3 polycyclic hydrocarbons, 2 aflatoxins, and 2 antitumor antimicrobials. Among the 21 carcinogens ineffective as prophage inducers were 3 aromatic amines (other than 2-aminoanthracene), 3 azo-aminoazo compounds, 2 methanesulfonates, and 2 nitro aromatics. In contrast, 18 and 17 of the 30 animal carcinogens were detected as genotoxic agents in the Salmonella/Ames test and E. coli WP2/ WP100 rec assay, respectively. The threshold sensitivity of the inductest was less than that of the Salmonella/Ames test for chemicals genotoxic in both tests. The ineffectiveness of the inductest as a routine test for detecting potential chemical carcinogens may be related to the nature of the DNA damage lesions formed by various genotoxic agents.     

Movement characteristics and power output of guinea-pig and hamster spermatozoa in relation to activation

Spermatozoa were collected from the cauda epididymidis of golden hamsters and guinea-pigs, and the acrosome reaction was induced in vitro. Movement characteristics of the spermatozoa were assessed with high-speed cinemicrography. Before the initiation of the acrosome reaction (preactivated spermatozoa), sperm movement in both species was characterized by progressive swimming by regular flagellar waves of moderate amplitude and relative high frequency. After the acrosome reaction (activated spermatozoa), sperm movement in both species was not progressive, and was characterized by whiplash-like flagellar undulations of significantly (P less than 0.05) higher amplitude and lower frequency. Calculation of the hydrodynamic power output by a new theory indicated that no significant change occurred after activation.     

Inhibition of 3,4-dihydroxy-l-phenylalanine decarboxylase in rat striatal synaptosomes by amino acids interacting with substrate transport

Dopamine synthesis from 3,4-dihydroxy-l-phenylalanine in rat striatal synaptosomes was inhibited by a number of amino acids with aromatic or large aliphatic side chains. Inhibition was not seen when aromatic amino acid decarboxylase activity was measured in disrupted synaptosomes. Similarly, inhibition of dopamine synthesis from tyrosine was seen in the presence of leucine. The inhibition most likely results from interactions of the amino acids with substrate transport across the synaptosome plasma membrane, rather than directly with the catalytic enzymes. The kinetic data obtained are used to infer information about the relevant transport process; they suggest the potential importance of amino acid efflux as a regulatory step.