Lloyd Barr

Intercellular Connection between Smooth Muscle Cells: the Nexus

High-resolution electron microscopy has revealed that the regions of contact between smooth muscle cells from dog intestine are areas of fusion of adjacent cell membranes. For morphological and functional reasons this type of contact between excitable cells has been termed a nexus.

Localization of rhodopsin antibody in the retina of the frog

Abstract A specific immune serum against frog rhodopsin has been developed in rabbits. The specificity of the antirhodopsin serum was established using the indirect Coons antibody technique. Absorption of the serum with electrophoretically purified rhodopsin abolished its ability to stain sections of retina or isolated retinal receptor disk membranes. Using fluorescein-labeled sheep anti-rabbit γ-globulin on sections of retina treated with antirhodopsin γ-globulin, fluorescence was observed in all retinal receptor outer segments and in the myoids and ellipsoids of retinal receptor inner segments. In addition, it was localized in cytoplasmic structures of the pigmented epithelium. Dissected retinas with intact outer segments showed fluorescence in the outer segments when the retinas were treated with antirhodopsin immune serum, washed thoroughly, incubated in fluorescein-labeled sheep anti-rabbit γ-globulin and again washed thoroughly. This is suggestive of a diffusion pathway into the outer segments. Isolated whole rod outer segments and isolated disk membranes stained uniformly by the indirect technique. From these observations we conclude that the photopigment is indeed part of the disk membranes of the outer segments and that the external membrane of the outer segment also contains photopigment. Use of the specific antirhodopsin immune serum has allowed the description of the molecular arrangement of photopigment in retinal receptor disk membranes (Blasie, Worthington & Dewey, 1968; Blasie & Worthington, 1969).

Durations of the after-images of brief light flashes and the theory of the Broca and Sulzer phenomenon.

Measurements were made of the time interval between the primary stimulus and the moment of disappearance of every trace of the after-image for flashes of very intense lights of variable duration. The results can be explained on the assumption that the duration of the after-image is determined by the time that it takes for the product of a photochemical reaction to fall to some threshold value. Certain predictions from this hypothesis are experimentally verified.

Propagation in Vertebrate Visceral Smooth Muscle

Abstract Smooth muscle cells behave electrically as if their interiors were directly connected without an intervening extracellular space. Although both light and electron microscope studies indicate that they do not comprise a true syncytium, regions of contact between the membranes of two cells have been described. This special kind of contact could account for all the present data and it is suggested the term “nexus” be applied to this structure because of its functional significance.

The path of intercellular communication: Gap junctions

Abstract The interconnections via gap junctions in smooth muscle tissues are important determinants of tissue responses. In smooth muscle the effects of neuromuscular transmission must always spread from myocyte to myocyte. If the innervation density is low with only one myocyte in many receiving viable inputs, then the role of gap junctions in coordinated tissue response becomes more critical to function. Although smooth muscle is characterized as having low innervation density, precise information is still largely lacking. Moreover, all gap junctions are not the same. The biophysical studies show homotypic Cx43 channels to be the most frequently occurring type in select mammalian smooth muscles. The permselectivity properties of these connexon channels permit the transfer of a variety of small solutes. Although dynamic changes in permselectivity properties are possible for Cx43 channels, their gating characteristics argue for downregulation as the predominant cellular mechanism in affecting cell-to-cell coupling. Thus, it is probable that Cx43 trafficking and properties such as mode shifting seem to the main mechanisms for dynamic change in cell-to-cell communication. Mode shifting appears to rapidly reduce the number of functioning channels relative to the slower trafficking of hemichannels.