Hypertrophic smooth muscle. III. Increase in number and size of gap junctions

Cases of intestinal smooth muscle hypertrophy/hyperplasia in pigeon and chickens

Intestinal smooth muscle hypertrophy and hyperplasia has been described in human and several mammal species. In birds, only one case of intestinal smooth muscle hyperplasia has been reported. This paper describes the anatomopathological and histological findings of three cases of intestinal smooth muscle hypertrophy/hyperplasia in two different avian species belonging to the family Gallinidae and Columbidae. Grossly, it involved all tracts of the small intestine. Histologically, hyperplasia involved the mucosal villi, muscularis mucosa and inner and outer layers of the tunica muscularis. Hypertrophy was apparently detected only in the inner circular muscle layer. Lack of submucosal plexuses was also observed in all three animals. The results confirm the remarkable histological difference between mammals and avian species and show as these pathological changes can occur in different species of birds.

Phasic and tonic smooth muscle function of the partially obstructed guinea pig intestine

This study was to generate phasic and tonic stress-strain curves for evaluation of smooth muscle function in the obstructed guinea pig jejunum. Partial and sham obstruction of the jejunum in guinea pigs was created surgically, with guinea pigs not being operated on served as normal controls. The animals survived 2, 4, 7, and 14 days, respectively. The jejunal segment was distended to 10 cm H₂O. The pressure and outer diameter changes were recorded. Passive conditions were obtained by using papaverine. Total phasic, tonic, and passive circumferential stress and strain were computed from the diameter and pressure data with reference to the zero-stress-state geometry. The active phasic and tonic stresses were defined as the total phasic and tonic stress minus the passive stress. The thickness of intestinal muscle layers increased in a time-dependent manner after obstruction. The amplitude of passive, total phasic, total tonic, active phasic, and active tonic circumferential stresses increased as function of strain 7 days after obstruction. However, when normalized to muscle layer thickness, the amplitude of active stresses did not differ among the groups. In conclusion, the long-term-obstructed intestine exhibits increased total smooth muscle contraction force. However, the contraction force per smooth muscle unit did not increase.

Biomechanical remodelling of obstructed guinea pig jejunum

Data on morphological and biomechanical remodelling are needed to understand the mechanisms behind intestinal obstruction. The effect of partial obstruction on mechanical properties with reference to the zero-stress state and on the histomorphological properties of the guinea pig small intestine was determined in this study. Partial obstruction and sham operation were surgically created in mid-jejunum of guinea pigs. The animals survived 2, 4, 7, and 14 days. The age-matched guinea pigs that were not operated served as normal controls. The segment proximal to the obstruction site was used for histological analysis, no-load state and zero-stress state data, and distension test. The segment for distension was immersed in an organ bath and inflated to 10cm H(2)O. The outer diameter change during the inflation was monitored using a microscope with CCD camera. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. The opening angle and absolute value of residual strain decreased (P<0.01 and P<0.001) whereas the wall thickness, wall cross-sectional area, and the wall stiffness increased after 7 days obstruction (P<0.05, P<0.01). Histologically, the muscle and submucosa layers, especially the circumferential muscle layer increased in thickness after obstruction. The opening angle and residual strain mainly depended on the thickness of the muscle layer whereas the wall stiffness mainly depended on the thickness of the submucosa layer. In conclusion, the histomorphological and biomechanical properties of small intestine (referenced for the first time to the zero-stress state) remodel proximal to the obstruction site in a time-dependent manner.

Intestinal chronic obstruction affects motor responsiveness of rat hypertrophic longitudinal and circular muscles

Extensive morphological and neurochemical changes have been experimentally and clinically documented in the hypertrophied intestine located orally to a chronic partial stenosis of the lumen. Functional studies revealed not only disruption of the interdigestive motor complex in vivo and decreased efficiency of contraction but also preservation of the peristaltic reflex in vitro. Given the critical role played in intestinal peristalsis by the coordinated activity of the longitudinal (LM) and circular muscle (CM), this work focuses on the motor responses of LM and CM isolated from rat hypertrophied ileum following mechanical obstruction. Maximal contractions to both receptor (acetylcholine and substance P) and non-receptor (K+) mediated stimuli were up to 10-fold increased in hypertrophic CM rings compared with control tissues, while a higher potency of substance P was revealed in both hypertrophied muscle layers. Relaxations to vasoactive intestinal polypeptide and 8-Br-cGMP were more intense on prostaglandin F(2alpha)-contracted hypertrophic LM strips compared with control tissues and a general tendency towards increased relaxation was shared also by hypertrophic CM basal tone. The present results collectively suggest that hypertrophic growth leads to hyperresponsiveness to contractile agents, particularly evident in the CM, and to increased sensitivity to relaxing mediators, especially exhibited by the LM. In this regard, the complementary role exerted by each muscle layer and the plasticity of the intestinal tissue could both come into play to preserve the intestinal functions in a changing environment.

Changes in expression of P2X1 receptors and connexin 43 in the rat myometrium during pregnancy

OBJECTIVE

To investigate the expression of P2X(1) receptors and connexin 43 in gap junctions between smooth muscle cells. Contraction mediated by P2X receptors is known to occur in the bladder and male reproductive tract, and cell-cell coupling of smooth muscle via gap junctions is essential for synchronized rhythmic activity of these tissues.

DESIGN

We selected for this study rat myometrial smooth muscle during pregnancy and at postpartum day l.

SETTING

University medical school.

ANIMAL(S)

Laboratory rats.

INTERVENTION(S)

Rats were mated and became pregnant.

MAIN OUTCOME MEASURE(S)

Immunostaining and fluorescence and confocal microscopy.

RESULT(S)

The level of P2X(1) receptor expression remained low throughout pregnancy (days 4 to 20) but was greatly up-regulated at day 22 (postpartum day 1). Connexin 43 expression showed a pattern of up-regulation, with progression through pregnancy and peaking near labor, but exhibited a rapid down-regulation after parturition.

CONCLUSION(S)

The functional significance of the changes in connexin 43 and P2X(1) receptor expression that have been observed is discussed in relation to triggering and modulation of uterine contractility during and after pregnancy.

Contractile function of the mechanically lengthened intestine

BACKGROUND

The application of longitudinal mechanical force induces lengthening of the small intestine. The purpose of this study is to evaluate the contractile function of the mechanically lengthened jejunum in a rodent model.

MATERIALS AND METHODS

Three groups of rats including normal jejunum, isolated jejunal segment without mechanical lengthening, and isolated lengthened jejunal segment, were studied for contractile function. The isometric contractions of jejunal segments were investigated in organ baths for spontaneous activity and response to potassium chloride and cholinergic carbachol.

RESULTS

The normal control group showed a basal spontaneous activity with an average frequency of 33 +/- 0.68 contractions per min (cpm). The basal spontaneous activity for the isolated group had an average frequency of 26 +/- 2.7 cpm and for the lengthened group had an average frequency of 24 +/- 5.7 cpm. Although the normal control group had a higher frequency of basal spontaneous activity as compared to either the isolated or lengthened groups, there was no statistically significant difference between the frequencies in the isolated and the lengthened groups. All three groups demonstrated a sustained increase in tension upon administration of either potassium chloride or carbachol.

CONCLUSIONS

The response to pharmacological stimulation, as measured by total area under the tension curve and maximal change in basal tone, was larger in the normal group than in the isolated groups. The addition of longitudinal mechanical force to lengthen the isolated jejunal segment did not further alter this change.

Motor responses of rat hypertrophic intestine following chronic obstruction

The present work aims at investigating the changes in motor responsiveness of rat intestine hypertrophied by chronic mechanical obstruction. Motor responses to pharmacological agents and electrical field stimulation (EFS) were studied in hypertrophic ileal segments excised from rats subjected to experimental stenosis (n = 20) and compared with responses of control tissues from sham-operated animals (n = 20). Spontaneous motility and contractile responses to exogenous agents (KCl, acetylcholine and substance P) and EFS (10-s trains every minute, 120 mA, 0.5 ms, 1-10 Hz) were increased in hypertrophic longitudinal segments; however, normalization of motor responses to tissue wet weight revealed a remarkable reduction of contractile efficiency in hypertrophied tissues coupled with a loss of sensitivity to nitric oxide-mediated relaxation. Furthermore, EFS under non-adrenergic non-cholinergic (NANC) conditions unveiled a major role of the cholinergic component over the peptidergic one in the neurogenic contraction of hypertrophic intestine. On the whole, hypertrophic intestinal growth emerges as a dynamic process entailing adaptation of smooth muscle and neuronal structures to the increased functional load imposed by lumen obstruction.

Hypertrophy of intestinal smooth muscle in cats

Pathological findings of four cats with severe and diffuse smooth muscle hypertrophy of the small intestine (MHSI) are reported and compared to those of five cats with segmental MHSI secondary to neoplastic obstruction and four controls. Histology demonstrated a constant association between idiopathic MHSI and submucosal fibrosis and chronic lymphoplasmacytic enteritis. Morphometry (gut diameter, thickness and area of muscular layers, number and density of smooth muscle nuclei) and MIB-1-immunolabelling showed that the thickness increase was mostly due to hypertrophy, but hyperplasia was also evident. Microbiology from ileal content samples was performed in two cats with primary MHSI, and Campylobacter spp. were isolated, which were also demonstrated by immunohistochemistry and ultrastructure. The association of chronic enteritis with idiopathic MHSI suggests that factors released in intestinal inflammation may also act as hypertrophy stimuli for smooth muscle cells.

Decreased shortening velocity and altered myosin isoforms in guinea-pig hypertrophic intestinal smooth muscle

The aims of this study were to investigate whether hypertrophy of the small intestinal smooth muscle leads to alterations of myosin isoform composition and shortening velocity and whether possible changes correlate with a change in the sensitivity to ADP of shortening velocity in this tissue. A partial occlusion was introduced in the distal part of the ileum of guinea-pigs. After 2 weeks, the part of the small intestine just proximal of the stenosis was hypertrophied (indicated by a significantly increased cross-sectional area). The most proximal part of the small intestine was used as control, thus enabling comparisons between hypertrophic and normal tissue from the same animal. The outer longitudinal layer of the intestinal wall was gently peeled off and used for biochemistry, RT-PCR and mechanical experiments. The desmin/actin ratio was significantly increased following hypertrophy, although myosin and actin expression were similar in control and hypertrophic tissue. In hypertrophic tissue, the myosin heavy chain mRNA with a 21 base pair insert decreased significantly. The composition of the mRNA encoding the myosin essential light chains changed towards more of the basic type (LC17b). No change in the expression of non-muscle myosin heavy chains A and B was detected. The maximal shortening velocity (V(max)) of maximally activated skinned preparations was significantly lower in the hypertrophic tissue (~50 % of control). The sensitivity of V(max) to ADP was increased in the hypertrophic smooth muscle tissue. We conclude that myosin expression is altered following intestinal hypertrophy and that these alterations affect reactions in the cross-bridge interaction, leading to a slower and more economical contractile function.

Role of altered responsiveness of hypertrophic smooth muscle in manometric abnormalities of the obstructed opossum oesophagus

The movements of the obstructed oesophagus are abnormal, but whether this relates to the disease causing the obstruction, to the altered load conditions or to abnormal neuromuscular functions in hypertrophic smooth muscle is unclear. In an opossum model of chronic oesophageal obstruction, we compared the mechanical responsiveness of hypertrophic smooth muscle in vitro to in vivo manometric function. Related to their greater thickness, strips of hypertrophic muscle generated greater force in response to electrical stimulation and to stretch than control strips. Hypertrophic muscle often generated repetitive contractions; spread of contractions orad from the stimulus site was common in hypertrophic oesophageal bands. On manometry, the obstructed oesophagus generated abnormally high pressures proximally, and highly variable pressure amplitudes in the middle and distally; pressure waves often occurred simultaneously throughout the oesophagus, were repetitive or multi-peaked and led to a lasting rise of oesophageal pressure. Alterations in the intrinsic neuromuscular functions of hypertrophic smooth muscle including generation of greater force, repetitive or spontaneous contractions, and retrograde spread of contractions explain many, but not all, of the manometric abnormalities seen in the chronically obstructed oesophagus.

An ultrastructural analysis of the epithelial-fiber interface (EFI) in primate lenses

The purpose of this study was to conduct a comprehensive ultrastructural analysis of the epithelial-fiber interface (EFI) in normal adult primate (Macaque nemestrina and fascicularis; 6-9 years old, n = 10) lenses. Scanning electron microscopy (SEM) was used to initially characterize the gross size, shape and three-dimensional organization of central zone (cz) epithelial cells and the anterior ends of elongating fibers beneath these cells. This fiducial information was essential to properly orient lens pieces in freeze fracture specimen carriers for the production of replicas with unambiguously identifiable EFI. Transmission electron microscopy (TEM) of replicas and thin-sectioned material were used to ultrastructurally analyse the cz EFI. TEM thin-sectioned material was also used to ultrastructurally analyse the pregerminative (pgz), germinative (gz) and transitional zone (tz) EFI. Correlative SEM and TEM of cz EFI components revealed that the apical membrane of both epithelial and elongating fiber cells were irregularly polygonal in shape, and aligned in parallel as smooth, concave-convex surfaces. However, whereas epithelial cell apical surfaces had minimal size variation, elongating fibers were larger and considerably variable in size. Quantitative analysis of > 10000 micron2 cz elongating fiber apical surfaces failed to detect any gap junctions defined in freeze fracture replicas as complementary aggregates of transmembrane proteins (connexons) conjoined across a narrowed extracellular space. However, a comparable frequency of vesicular events was noted in this region as quantified previously in adult and embryonic chick lens. Correlative TEM analysis > 1500 linear micrometers of thin-sectioned EFI from this region confirmed the presence of epithelial-epithelial gap junctions, elongating fiber-elongating fiber gap junctions, and an extreme paucity of epithelial-elongating fiber gap junctions. In contrast, TEM analysis of > 1000 linear micrometers of thin-sectioned pgz, gz and tz EFI, confirmed the presence of epithelial-epithelial gap junctions, elongating fiber-elongating fiber gap junctions, numerous epithelial-elongating fiber adherens junctions and a few epithelial-elongating fiber gap junctions. Thus, the results of this and previous quantitative morphological and physiological studies (electronic and dye coupling) demonstrate that there is limited coupling between cz epithelial cells and underlying elongating fibers. Furthermore, the absence of gap junctional plaques in cz EFI freeze-fracture replicas and either pentalaminar or septalaminar profiles in correlative thin-sections, suggests that this limited coupling could be mediated via isolated gap junction channels. However, the results of this and previous quantitative studies further show that a greater degree of coupling exists across the pgz, gz and tz regions of the EFI and that this coupling is likely to be mediated by gap junction plaques. Finally, this and other studies continue to demonstrate that transcytotic processes play a role in lens physiology at the EFI.

Structural basis of geriatric voiding dysfunction. IV. Bladder outlet obstruction

Several aspects of the pathogenesis of voiding dysfunction in bladder outlet obstruction remain unresolved. The structural basis of obstructive versus nonobstructive dysfunction was investigated in a prospective ultrastructural/urodynamic study of 35 elderly subjects of comparable age. Detrusor structure was examined by electron microscopy, with blinded clinical and urodynamic information. Seven detrusor specimens were segregated by a distinctive myohypertrophy, structural pattern, which matched with 6 male and 1 female subjects 72 to 96 years old (mean age 83) who had urodynamically proved outlet obstruction. This pattern was characterized by widely separated muscle cells with reduction of intermediate cell junctions, collagenosis, that is abundant collagen plus some elastic fibers, in the markedly widened spaces between individual muscle cells and abundant profiles characteristic of enlarged, hypertrophic muscle cells. Superimposed degeneration of muscle cells and axons in 6 specimens matched those of 5 men and 1 woman who had impaired detrusor contractility. In 3 specimens there were also abundant protrusion junctions and ultra-close abutments; these matched those of 2 men and 1 woman with obstruction plus detrusor overactivity. Observations on the degree of bladder trabeculation in the entire population of 35 subjects are presented. It is concluded that bladder outlet obstruction is associated with changes in detrusor structure that can account for the resultant voiding dysfunction. Features of the myohypertrophy pattern, with or without superimposed degeneration, can explain overall weakness of the obstructed detrusor despite hypertrophy of its cells. Protrusion junctions and abutments probably mediate electrical coupling of muscle cells leading to involuntary contractions in the overactive (unstable) obstructed detrusor. Excessive deposits of elastic fibers (hyperelastosis) between widely separated muscle cells and in interstitium are suggested as the probable structural basis for increased bladder distensibility and chronic retention.

Idiopathic muscular hypertrophy of the equine small intestine: 11 cases (1980-1991)

The medical records of 11 horses with idiopathic muscular hypertrophy (MH) of the small intestine were reviewed to determine the clinical and pathological features of the disease. The median age of affected horses was 10.0 years (range 5-18 years). No breed or sex predisposition was apparent. Ten horses (91%) had chronic (23 days to 2.4 years) signs of mild, intermittent colic, and 1 horse had signs of severe colic of only 3 days' duration. Partial anorexia and chronic weight loss of variable duration (1-6 months) were prominent historical findings in 5 (45%) horses. Diagnostic tests, with the exception of exploratory caeliotomy, were ineffective for definitive diagnosis of intestinal MH as a cause of colic. In 2 horses, however, a thickened, rigid ileum was detected by palpation per rectum, and in 5 horses, multiple loops of distended small intestine were detected by palpation per rectum. Hypertrophy of both the circular and longitudinal layers of muscularis was determined as the cause of intestinal thickening in all horses. Muscular hypertrophy of the ileum was present in 9 (82%) horses. Two horses (18%) had MH of a section of jejunum only, and 4 (36%) horses had MH of the ileum in combination with MH of other sections of small intestine. Two (18%) horses had MH of the entire small intestine. In 9 (82%) horses, intestinal MH resulted in narrowing of the luminal diameter at the site of MH. Small diverticula were present on the mesenteric border of the hypertrophied ileum of 5 (45%) horses. Five linear (up to 150-cm) diverticula were present in the hypertrophied jejunum of 1 (9%) horse. Haemomelasma ilei was present on the antimesenteric serosal surface of affected intestine of 8 (73%) horses. Full-thickness rupture of the ileum with subsequent diffuse, septic peritonitis occurred in 3 (27%) horses.

Hypertrophic smooth muscle in the partially obstructed opossum esophagus. Excitability and electrophysiological properties

Partial obstruction of the opossum esophagus leads to thickening of the circular muscle, hypertrophy of smooth muscle cells, and diminution of the extracellular space. The pharmacological and electrophysiological properties of this hypertrophied muscle were studied. Carbachol produced phasic and tonic contractions of the circular muscle. The EC50 for tonic contractions was greater for hypertrophied than for normal muscle (21.1 +/- 3.9 mumol/L vs. 4.8 +/- 2.2 mumol/L; P less than 0.05). The resting membrane potential difference of hypertrophied muscle (-50.8 +/- 0.2 mV) was similar to that of normal muscle (-50.0 +/- 0.2 mV). Electrical stimulation of intrinsic nerves in the normal muscle produced a hyperpolarization followed by a depolarization of smooth muscle membrane potential. Hypertrophied muscle responded either with an attenuated hyperpolarization or no hyperpolarization, both of which were followed by a depolarization. The space constant in the long axes of the hypertrophied circular muscle cells was greater than normal (4.4 +/- 0.2 mm vs. 3.4 +/- 0.1 mm; P less than 0.001). The threshold potential for initiation of action potentials was more negative for hypertrophied (-43.2 +/- 0.4 mV) than for normal circular muscle (-41.6 +/- 0.2 mV; P less than 0.005). These data indicate that alterations in neuromuscular function accompany the hypertrophy of esophageal smooth muscle.

Gap-junction quantification in biological tissues: freeze-fracture replicas versus thin sections

The relative efficiency of freeze-fracture replicas versus thin sections for the visualization and quantification of gap junctions in biological tissues has been evaluated. Both methods may underestimate gap-junction number--thin sections for reasons of tissue resolution and freeze-fracture replicas due to the mechanics of the fracturing process. Freeze-fracture misses gap junctions in regions of plasma membrane which are highly contoured, such as the overlapping basal cell processes of Drosophila imaginal wing discs and the interdigitating lateral membrane plications of intercalated discs in cardiac tissue. If the missed gap junctions are relatively large, as they are in both of these examples, freeze-fracture significantly underestimates the total gap-junctional area. Thin sections may miss small gap junctions, but in tissues which contain a range of gap-junction sizes the lost junctions constitute a relatively small fraction of the total junctional area. In neoplastic imaginal wing discs, thin sections were as efficient as freeze-fracture replicas in identifying even the smallest gap junctions. Although freeze-fracture may be the better technique for the qualitative and quantitative documentation of small gap junctions in tissues with relatively flat to gently contoured plasma membranes and thin sections may be the superior method for gap-junction quantification in tissues containing a range of gap-junctional sizes and highly contoured cellular processes, the data suggest that a combination of the two approaches should be utilized whenever possible.

Hypertrophy of visceral smooth muscle

Smooth muscles of viscera undergo a large increase in volume when there is a chronic, partial obstruction impairing the flow of lumenal contents. Hypertrophy of smooth muscle occurs in various medical conditions and several methods are available for inducing it experimentally in laboratory animals, especially in urinary bladder, small intestine and ureter. The hypertrophic response differs somewhat with the type of organ, the animal species, the age of the subject, and the experimental procedure. Ten- to fifteen-fold increases in muscle volume develop within a few weeks in the urinary bladder or the ileum of adult animals, a growth that would not have occurred in the lifespan of the animal without the experimental intervention. The general architecture of the muscle and the boundaries with adjacent tissues are well preserved. In intestinal hypertrophy, muscle cells increase in number: mitoses are found in mature, fully differentiated muscle cells. Cell division by full longitudinal splitting of muscle cells may also occur. Enlargement of muscle cells accounts for most of the muscle hypertrophy. The hypertrophic muscle cell has an irregular profile with deep indentations of the cell membrane, bearing caveolae and dense bands; however, the cell surface grows less than the cell volume (reduction of surface-to-volume ratio). The nucleus is crenated and is much less enlarged than the cell (reduction of the nucleo-plasmatic ratio). Mitochondria grow in number but in some muscles their spatial density decreases; intermediate filaments increase more than myofilaments. The spatial density of sarcoplasmic reticulum is generally increased. In the hypertrophic intestine, gap junctions increase in number and size; in the bladder, gap junctions are absent both in control and in hypertrophy. Thus the hypertrophic muscle cell is not only larger than a control cell, but has a different pattern of its structural components. Extensive neo-angiogenesis maintains a good blood supply to the hypertrophic muscle. The density of innervation is much decreased in the hypertrophic intestine, whereas it appears well maintained in the bladder. Neuronal enlargement is found in the intramural ganglia of the intestine and in the pelvic ganglion. The mechanisms involved in hypertrophic growth are unknown. Three possible factors, mechanical factors, especially stretch, altered nerve discharge, and trophic factors are discussed.

Myenteric plexus neuropathy in infantile hypertrophic pyloric stenosis

The myenteric plexus and intramuscular nerve bundles in the circular muscle layer of the pylorus from 37 children with infantile hypertrophic pyloric stenosis (IHPS) obtained at pyloromyotomy were studied by light and electron microscopy and compared to six control cases without clinical evidence of IHPS. In certain IHPS cases degenerative alterations of the axons predominated. The axonal changes consisted of (1) severely increased variability of diameters with evidence of degeneration and regeneration of some axons, (2) accumulation of electron-dense bodies, lysosomes and pleomorphic membranous cytoplasmic bodies, (3) increase in the number of maloriented neurofilaments, and (4) aggregation of glycogen granules. Degenerative changes or immaturity of perikarya of neurons and glial cells in the myenteric plexus were not a significant feature. While axonal changes predominated in some IHPS cases there were severe changes of smooth muscle cells in others suggesting that a primarily neurogenic type of IHPS can be distinguished from a predominantly myogenic type. Although the etiology of the axonal changes in IHPS is not clear, it is suggested that they play an important role in the pathogenesis of pyloric stenosis and hypertrophy.

Changes in intercellular electrical coupling of smooth muscle accompanying atrophy and hypertrophy

Longitudinal tissue impedance was determined for cat circular intestinal muscle that was either hypertrophied due to volume overloading or atrophied due to defunctionalization. These conditions were produced by bypassing 50 cm of jejuno-ileum in six cats and, 2-6 mo later, removing segments from the proximal jejunum of the hypertrophied functional gut and from the atrophied proximal end of the bypassed loop. Impedances were compared with those of jejunal circular muscle from 15 normal cats. Specific tissue impedance was determined by a modification of the method of Tomita (J. Physiol. Lond. 201: 145-159, 1969), which employs Krebs and Krebs-sucrose solutions; a tissue shrinkage of 5%, empirically found to occur in Krebs-sucrose solution, was corrected for. Impedance values were determined at 20 frequencies between 30 Hz and 30 kHz. The value at 30 kHz was taken to represent the specific myoplasmic resistance (Rmyo) of each tissue, while the difference between the value of 30 Hz and 30 kHz was taken to represent the specific junctional resistance (Rj). Values (in omega X cm) for Rmyo were control 134 +/- 2, functional 128 +/- 5, bypassed 151 +/- 6 (mean of means +/- SE). Corresponding values for Rj were control 173 +/- 15, functional 96 +/- 27, bypassed 340 +/- 75. Calculated values (in microF/cm) for junctional capacitance were control 2.66, functional 6.10, bypassed 1.97. Acid uncoupling by saturating the bathing solutions with 100% CO2 revealed a pH-sensitive resistive component of Rj, assumed to be attributable to gap junctions.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat bladder in the early stages of streptozotocin-induced diabetes: adrenergic and cholinergic innervation

The adrenergic and cholinergic innervation of the bladder was studied in streptozotocin-diabetic rats. The presence of hypertrophy and distension in the 'diabetic' bladders necessitates care in assessing changes occurring in the nerves, factors which are also relevant to clinical histochemical studies. Biochemical assays of cholinergic enzymes revealed decreased activities per g wet weight tissue. However, the total activities of choline acetyltransferase and acetylcholinesterase per whole bladder were significantly increased after 2 weeks of diabetes with greater changes by 8 weeks. Total dopamine levels per bladder were significantly higher than in control rats in the 2-week but not the 8-week group of animals; this may indicate an initial increase in adrenergic nerve activity. There was no impairment in the ability of the detrusor muscle to respond to noradrenaline, acetylcholine or to cholinergic nerve stimulation. Shortly after induction of diabetes streptozotocin-treated rats display polyuria. It is proposed that the activity of the bladder is therefore stimulated to allow greater volumes of urine to be passed. The results are discussed in relation to human diabetes mellitus where clinical studies have implicated a neuropathic origin to bladder dysfunction.

Gap junctions of the muscles of the small and large intestine

The distribution of gap junctions (nexuses) in various parts of the small and large intestines of the guinea-pig was studied using the freeze-fracture technique and in thin sections. The percentage area of smooth muscle cell surface occupied by gap junctions varies from 0.50% in the circular muscle of the duodenum to zero in the longitudinal muscle of the ileum. In the circular muscle of the jejunum and ileum the area occupied by nexuses is 0.22% (or about 11 micrometers 2 per cell). The sizes of junctions range from less than 0.01 micrometer 2 to 0.20 micrometer 2, with two-thirds of them being smaller than 0.05 micrometer 2. In the colon, gap junctions are rare, very small and confined to the circular muscle layer. Even the smallest aggregates of intramembrane particles correspond to areas of close apposition between the membranes of adjacent cells; it is therefore justified to interpret them as being gap junctions. Some gap junctions are formed between a smooth muscle cell and an interstitial cell. Gap junctions are not found in the longitudinal muscle of the small intestine; this is in sharp contrast to the abundance of gap junctions in the adjacent circular layer. In the small intestine of cats and rabbits, gap junctions are abundant in the circular muscle layer, whereas they are very small in size and very few in number in the longitudinal muscle layer.

Effects of ovarian steroids and pregnancy on adrenergic nerves of uterus and oviduct

This review concerns the influence of ovarian steroids and of pregnancy on norepinephrine (NE) metabolism in the adrenergic neurons of the female reproductive tract and speculates on the physiological consequences of this influence. Estrogen and progesterone affect not only the NE content of these nerves but also the turnover of NE, the activity of its synthetic enzyme, and releases of NE from nerve terminals. During pregnancy additional factors including stretch-induced hypertrophy come into play and cause degeneration of the nerves in the uterine corpus. This degeneration makes the muscle supersensitive to NE and may also induce morphological changes in the muscle cell membrane. As a result there may be a withdrawal of neural inhibitory influences on the corpus, allowing spontaneous myogenic contractions to intensify. Although the physiological significance of the steroid-transmitter interactions are still unclear, these nerves per se are of interest because they represent a model system for the study of neuroendocrine regulation in the peripheral nervous system.

The bicellular and reflexive membrane junctions of renomedullary interstitial cells: functional implications of reflexive gap junctions

Renomedullary interstitial cells are loosely organized within the interstitial space surrounding collecting ducts, limbs of Henle, and capillaries of the rat renal medulla. These cells possess long processes, which interact with each other and with cell bodies to form bicellular tight, intermediate, and gap junctions. In addition, both cell bodies and cell processes possess "reflexive" gap and intermediate junctions. Possible functions of renomedullary interstitial cell membrane junctions are discussed. Particular attention is given to a consideration of the functional significance of "reflexive" gap junctions.