Nexuses between Areas of the Surface Membrane of the Same Arterial Smooth Muscle Cell

Specialized areas of close apposition (nexuses) are found between the smooth muscle cells of various organs (Dewey and Barr, 1962, 1964), including blood vessels (Cliff, 1967 ; Verity and Bevan, 1968; Devine and Simpson, 1968) . The nexus may appear as either a tight junction, with apparent membrane fusion, or a gap junction, possibly depending on the method of fixation (Brightman and Reese, 1969 ; and compare Cobb and Bennett, 1969 a with Uehara and Burnstock, 1970). These structures may be important in the conduction of electrical events which is known to occur between smooth muscle cells of various organs (Bozler, 1938 ; Tomita, 1967 ; Barr et al ., 1968; Abe and Tomita, 1968) . In addition, conduction between arterial smooth muscle cells is suggested by the successful use of the sucrose-gap method to record from this tissue (Keatinge and Richardson, 1963 ; Keatinge, 1964) . In the present work, intercellular junctions in arterial smooth muscle have been examined . Junctions between areas of the surface membrane from the same cell are also described and some implications of this finding are discussed .