Lis Engdahl Nielsen

Electron microscopy of filaments in the basal part of rat kidney tubule cells, and their in situ interaction with heavy meromyosin

SummaryBy electron microscopy, the prominent bundles of filaments occurring in the basal part of proximal and distal tubule cells and in interstitial cells of rat kidney cortex were studied in cells fixed by vascular perfusion, in glycerol-extracted cells and in glycerol-extracted cells treated with heavy meromyosin (HMM).The studies of perfusion-fixed tissue showed that the proximal tubule cells contained in their most basal part filamentous bundles oriented transversely around the tubule. The bundles consisted of trightly packed thin filaments (50–80 Å in diameter). Similar but less prominent bundles were found in distal tubule cells and in interstitial cells. The dimension of these filaments was similar to that of actin filaments and their insertion in the basal cell membrane of the tubule epithelial cells resembled the insertion of actin filaments in the cell membrane of smooth muscle cells.The studies on glycerol-extracted cells revealed that some tubule cells contained two types of filaments (60–80 Å and 130–170 Å in diameter) located side by side in the basal filamentous bundles. The dimension of the thick filaments corresponds well to the values for myosin filaments in glycerinated smooth and skeletal muscle.The studies on HMM-reacted renal tissue revealed that the thin filaments (60–80 Å) described in tubule and interstitial cells are probably actin filaments, as they formed characteristic arrowhead complexes morphologically indistinguishable from the complexes of HMM with actin filaments in smooth and striated muscle cells.Our results provide strong evidence that a two-filament contractile system, based on interaction of actin and myosin filaments, exists in renal tubule and interstitial cells. As a hypothesis it is proposed that it is changes in tonus of the basal filamentous system in the proximal tubule cells which stabilize the intratubular pressure, possibly via angiotensin.

A two-filament system and interaction of heavy meromyosin (HMM) with thin filaments in smooth muscle

SummaryThe structure of glycerinated smooth muscle from small intestine of adult rat was investigated by electron microscopy. In the central parts of the tissue blocks a two-filament system was found, consisting of parallel thick and thin filaments with regularly spaced interconnections, closely resembling that of striated muscle. In the peripheral parts of the blocks only thin filaments were found. The thin filaments were identified as actin by the formation of arrowhead complexes after incubation with heavy meromyosin.

Variations in myoneme birefringence in relation to length changes in Stentor coeruleus.

Abstract The stalk segment of the heterotrich ciliate, Stentor coeruleus , appears nearly isotropic in the contracted state and develops a characteristic birefringence during extension. The birefringence occurs in stripes and is associated with the myonemes, one of the two longitudinally running subpellicular fiber systems. Electron microscopical investigations reveal changes in the ultrastructure of the myonemes from the extended to the contracted state. The relaxed myonemes consist mainly of 3 nm filaments running in the longitudinal direction, while the contracted myonemes show 10 nm tubular-like filaments, more randomly oriented. It is suggested that during elongation the randomly oriented tubular filaments undergo a conformational change to more regularly arranged thin filaments, thus causing development of birefringence.

Effect of Synthetic Lysine-Vasopressin on Adenohypophysial Activity in Toads

Summary In toads (Bufo bufo (L.)) with deficient pars distalis function due to extirpation of median eminence, subcutaneous injection of synthetic lysine-vasopressin causes shedding of the hyperkeratinized stratum corneum. In hypophysectomized toads lysine-vasopressin is without effect. Lysine-vasopressin is thus able to stimulate pars distalis activity in toads, indicating a chemical relationship between pars nervosa and median eminence (adenohypophysiotropic) hormones.

Morphology and cytology of the olfactory organs in small juvenile Dascyllus aruanus and Amphiprion ocellaris (Pisces: Pomacentridae)

The olfactory organs in juvenile Dascyllus aruanus and Amphiprion ocellaris , studied by scanning and transmission electron microscopy (SEM and TEM), consisted of two bilaterally radial rosettes per specimen, fan-shaped, located medio-ventrally, one in each of two olfactory chambers. In D. aruanus the rosette comprises six lamellae, three on each side of a midline raphe; in A. ocellaris 12 lamellae, six on each side. In both species, the sensory regions in the lamellae are continuous, except for the margin of the lamellae, and richly covered with stereocilia. Areas with juvenile bipolar receptor cells were observed in both species. Two dissimilar types of olfactory receptor cells in the sensory epithelium: ciliated and microvillous were observed.

Contraction in Stentor coeruleus induced by electric stimulation

Abstract 1. 1. The contraction in Stentor coeruleus was studied by superposition-photomicrography. 2. 2. The applied electric stimulation was by square-wave pulses of 0·1–2·0 msec. 3. 3. The shortening was completed in about 9 msec and was an all-or-none phenomenon. 4. 4. The latency between stimulation and the onset of contraction was 1–3 msec. 5. 5. Summation of two subliminal stimuli was demonstrated.

Properties of the transition from short-term to long-term depression in neurons of Helix pomatia

Abstract 1. 1. Synaptic short-term depression could be transferred into long term depression by repetition of series of stimuli. 2. 2. The transition from short-term depression to long-term depression was blocked by puromycin. 3. 3. The majority of the transition took place during resting periods between stimulus series. 4. 4. The initiation of the transition process was 83% completed after 5 min of stimulation. 5. 5. Short- and long-term depression were quantitatively separated into their two serial sites of origin: afferent axons and synaptic terminals. 6. 6. Long sequences evoked periods with increased and variable EPSPs not conforming to depression.

High-speed cinematographic analysis of electrically induced contraction in Stentorcoeruleus

Abstract 1. 1. The time course of electrically induced contraction in Stentor coeruleus was studied by high-speed cinematography. 2. 2. After an electrical stimulus of duration 1 msec, the contraction was propagated and complete. 3. 3. Contraction could be elicited from any part of the animal; however, the necessary stimulus intensity varied according to the site of application and the polarity of the stimulating electrode.