Rapid mixing-vesicle ion flux and planar lipid bilayer-single channel measurements have shown that a high-conductance, ligand-gated Ca2+ release channel is present in 'heavy', junctional-derived membrane fractions of skeletal and cardiac muscle sarcoplasmic reticulum. Using the release channel-specific probe, ryanodine, a 30S protein complex composed of polypeptides of Mr approximately 400,000 has been isolated from cardiac and skeletal muscle. Reconstitution of the complex into planar lipid bilayers has revealed a Ca2+ conductance with properties characteristic of the native Ca2+ release channel.

Adenine Nucleotides↗

PubMedDate not supplied

Sarcoplasmic reticulum contains adenine nucleotide-activated calcium channels.

Rapid calcium efflux from the sarcoplasmic reticulum (SR) is a necessary step in excitation-contraction coupling in skeletal muscle and is thought to be mediated by a calcium channel. Calcium efflux has been studied in fragmented SR vesicles by radioisotope efflux and fluorescence measurements. Several laboratories have reported that adenine nucleotides can stimulate calcium efflux from SR. In recent reports, Ca2+ release with a first-order rate constant as high as 100 s-1 has been observed for nucleotide-stimulated Ca2+ release from SR vesicles. Also, radioisotope efflux was blocked by Mg2+ and micromolar concentrations of the polycationic dye, ruthenium red. These high rates of transport are difficult to reconcile with a mechanism other than passive diffusion through a nucleotide-activated 'calcium release channel'. Using the fusion technique for inserting SR proteins into planar lipid bilayers, we report here single-channel recordings of calcium release channels from purified 'heavy' SR membranes. Channels have been identified on the basis of their activation by adenine nucleotides, blockade by ruthenium red, and selectivity for divalent cations. Surprisingly, the channel studied here exhibits an unusually large conductance of 170 pS in 50 mM Ba2+ while still being capable of discriminating against monovalent cations by a permeability ratio, P(Ba)/P(Cs) = 11.4.

Adenosine Triphosphate↗

PubMedDate not supplied

The value of animal models for study of infection due to atypical mycobacteria.

To elucidate the present significance of animal experimentation for the solving of taxonomic and epidemiologic questions arising in the study of the various species of the so-called atypical mycobacteria, experimental results in animals are presented. The Mycobacterium avium complex in particular is discussed in detail. Guinea pigs, rabbits, hens, and white mice were infected in different ways with various doses of the mycobacteria in question. The animals were killed after a given time unless they had died spontaneously. The findings are expressed in terms of survival time, macroscopic and microscopic appearance, and the results of cultures of the organs involved. The relationship between the course of the disease in humans and the virulence of the mycobacterial strains for animals is still not a close one. In general, large inocula of organisms are needed to set up lesions in experimental animals. M. Avium serovar strains are the most virulent to experimental animals.

Animals↗

PubMedDate not supplied

Comparison of CHAPS-induced current fluctuations with sarcoplasmic reticulum Ca2+ release channel activity.

The process of purifying and reconstituting transport membrane proteins generally involves the use of detergents, which often cannot be completely separated from the proteins. The effects of the zwitterionic detergent CHAPS on planar lipid bilayers have been measured, and it is demonstrated that CHAPS can induce microscopic electrical activity in the bilayers. Typical CHAPS-induced activity consists of large current bursts, often separated by intervals of quiescent activity, with no definable conductance levels. The size of the current bursts is generally increased by higher CHAPS concentration or by millimolar ATP and usually reduced by millimolar Mg2+ and micromolar ruthenium red. The response of the CHAPS-induced currents to these agents is compared to that of the ligand-gated Ca2+ release channel of muscle sarcoplasmic reticulum.

Animals↗