Activation of two types of fibres in ferret,Mustela putorius furo,cremaster muscle

Summary Some contractile, histochemical, morphological and electrophysiological properties of ferret, Mustela putorius furo, cremaster muscle have been estimated. Histochemical fibre typing revealed the presence of two types of fibres (type I 66.2%, type II 33.8%). Morphometry performed on ATPase-stained transverse sections showed that type I was composed of a large amount (40%) of small(<400 m²) cells. In mammalian Ringer two groups of fibres could be recognized on the basis of the values of resting potential (-69.7 mV and-59.1 mV) and intracellular sodium activity (8.3 mmol·l^-1 and 14.1 mmol·l^-1, respectively). In experiments on fibre bundles, the elevation of extracellular potassium concentration to 15–200 mmol·l^-1 produced contractures that consisted of a well-defined transient or phasic tension followed by a sustained or tonic tension. Properties of activation and inactivation of the tension analysed in small bundles of cut fibres (lengths 0.5–1.0 cm) were of fast- and slow-twitch type for phasic and tonic phase, respectively. In contrast to the phasic component of K contractures, the tonic phase was abolished by Ca²⁺ withdrawal and inhibited by Ni²⁺, Cd²⁺, Co²⁺, Gd³⁺ and gallopamil (D600). In Ca²⁺-free medium the sustained tension was restored by adding Sr²⁺. It is concluded that in ferret cremaster muscle the presence of slow-twitch fibres would give rise to the tonic component of the K contracture in which an extracellular source of activator Ca²⁺ is involved. The ability of these fibres to contract with a maintained tension for prolonged periods of time might participate in the temperature regulation of the testes.Abbreviations a _i ^Na intracellular sodium activity - ATPase myosin adenosine triphosphatase - D600 gallopamil - E _m membrane potential - E _r resting potential - EDL muscle, extensor digitorum longus muscle - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - e.c. excitation-contraction - SDHase succinate dehydrogenase - NADHase nicotinamide adenine, dinucleotide hydrogen-diaphorase - SOL muscle, soleus muscle - T time constant of relaxation - TEACI tetraethylammonium chloride - [Ca]_o, [K]_o, [Na]_o extracellular calcium, potassium, sodium concentration     

Differential sensitivity of cardiac K(ATP) + channels to guanine nucleotides — evidence for a heterogeneous channel population

In cell-free patches from cultured neonatal rat cardiocytes, the cytosolic presence of GTP--S (100 µmol/l) or GDP-\-S (100 µmol/1) activated K_(ATP) ⁺ channels. GTP--S required cytosolic Mg⁺⁺, suggesting that an activated G-protein causes the increase in open probability. The great variations of the channel response to GTP--S and GDP-\-S indicates that cardiac K_(ATP) ⁺ channels represent a heterogeneous family. Correspondence to: M. Kohlhardt     

Cardiovascular and renal effects of eel and rat atrial natriuretic peptide in rainbow trout,Salmo gairdneri

Summary The renal and in vitro vascular effects of atrial natriuretic peptides have been examined in seveal species of fish. However, comparatively few investigations have described the effects of these peptides on the cardiovascular system in vivo. In the present experiments the dorsal aorta and urinary bladder were cannulated and the effects of atrial natriuretic peptides from rat and eel were monitored in conscious trout during bolus injection or continuous atrial natriuretic peptide infusion. The results show that the initial pressor effect of atrial natriuretic peptides is independent of environmental salinity adaptation (fresh or seawater) and the chemical form of atrial natriuretic peptide injected, but it is affected by the rate of atrial natriuretic peptide administration. This pressor response, and the accompanying diuresis, are mediated through -adrenergic activation. Continuous infusion of either rat or eel atrial natriuretic peptide produces a steady fall in mean arterial blood pressure, which is temporally preceded by an increase in heart rate and a decrease in pulse pressure. Diuresis induced by atrial natriuretic peptides is only partially sustained during continuous infusion. Propranolol partially blocks the increase induced in heart rate by atrial natriuretic peptides, but does not affect either pulse pressure or mean arterial pressure. Propranolol significantly increases urine flow in saline-infused animals but has no apparent effect on animals subjected to infusions of atrial natriuretic peptides. These results indicate that there are multiple foci for the action of atrial natriuretic peptides in trout and that in many instances the effects of atrial natriuretic peptides are mediated through secondary effector systems.Abbreviations ANP atrial natriuretic peptide - bw body weight - PBS phosphate-buffered saline     

Steric aspects of agonism and antagonism at beta-adrenoceptors: synthesis of and pharmacological experiments with the enantiomers of formoterol and their diastereomers.

The enantiomers of formoterol (R;R and S;S) and their diastereomers (R;S and S;R) were synthesized and purified using a new procedure which required the preparation of the (R;R)- and (S;S)-forms of N-(1-phenylethyl)-N-(1-(p-methoxyphenyl)-2-propyl)-amine as important intermediates. The enantiomeric purity obtained was greater than 99.3%, usually greater than 99.7%. The four stereoisomers were examined with respect to their ability to interact in vitro with beta-adrenoceptors in tissues isolated from guinea pig. The effects measured were (1) relaxation of the tracheal smooth muscle (mostly beta 2), (2) depression of subtetanic contractions of the soleus muscle (beta 2), and (3) increase in the force of the papillary muscle of the left ventricle of the heart (beta 1). All enantiomers caused a concentration-dependent and complete relaxation of the tracheal smooth muscle which was inhibited by propranolol. The order of potency was (R;R) much greater than (R;S) = (S;R) greater than (S;S). There was a 1,000-fold difference in potency between the most and the least potent isomer. The presence of the (S;S)-isomer did not affect the activity of the (R;R)-isomer on the tracheal smooth muscle. Also on the skeletal and cardiac muscles (R;R)-formoterol was more potent than its (R;S)-isomer. The selectivity for beta 2-adrenoceptors appeared to be slightly higher for the (R;R)-isomer than for the (R;S)-isomer. The potency of the (S;R)- and (S;S)-isomers on the papillary muscle was too low to be determined accurately.(ABSTRACT TRUNCATED AT 250 WORDS)     

An in vitro model for cell-cell interactions

Summary Heterotypic cell-cell interactions appear to be involved in the control of development and function in a wide variety of tissues. In the vasculature, endothelial cells and mural cells (smooth muscle cells or pericytes) make frequent contacts, suggesting a role for intercellular interactions in the regulation of vascular growth and function. We have previously grown endothelial cells and mural cells together in mixed cultures and found that heterocellular contact led to endothelial growth inhibition. However, this mixed culture system does not lend itself to the examination of the effects of contact on the phenotype of the individual cell types. We have therefore developed a co-culture system in which cells can be co-cultured across a porous membrane, permitting intercellular contact while maintaining pure cell populations. Co-culture of endothelial cells and smooth muscle cells across membranes with pore sizes of 0.02, 0.4, 0.6, and 0.8μm maintained the two cell types as homogeneous populations, whereas smooth muscle cells migrated across the membrane through pores of 2.0μm. Vascular cell co-culture across membranes with 0.8-μm pores resulted the inhibition of endothelial cell proliferation and the generation of conditioned media which inhibited endothelial cell growth. The arrangement of the cells in this co-culture system mimics thein vivo orientation of vascular cells in which mural cells are separated from the abluminal surface of the endothelium by a fenestrated internal elastic lamina or basement membrane. Because this co-culture system maintains separable populations of cells in contact or close proximity allowing for biochemical and molecular analyses of pure populations, it should prove useful for the study of cell-cell interactions in a variety of systems.     

The comparison of vanadyl(IV) and insulin-induced hyperpolarization of the mammalian muscle cell

Extracellularly applied vanadyl(IV) hyperpolarized the membrane potential of mouse diaphragm muscle from about −74.0 mV up to −81.7 mV. The hyperpolarizing effect of 10⁻⁴ mol·l⁻¹ vanadyl(IV) is comparable with hyperpolarization induced by 100 mU·ml⁻¹ insulin. Both compounds increased the intracellular K⁺ concentration, the hyperpolarizing effect of vanadyl(IV) and insulin is blocked by ouabain and is unaffected by removal of K⁺ from the external medium. Triggering of the release of intracellular K⁺ associated with cellular proteins is proposed as the mechanism of vanadyl(IV) and insulin-induced hyperpolarization.     

Effect of cold environment on skeletal muscle mitochondria in growing rats

Summary Growing rats (4 weeks old) were kept for 3 weeks at 11° C and 24° C respectively. The cold-adapted animals showed a significantly higher oxygen consumption (64%). Volume density of subsarcolemmal and interfibrillar mitochondria as well as volume density of fat droplets were estimated in M. soleus and the diaphragm of both groups. In cold-adapted animals, the total volume of mitochondria was significantly increased by 24% in diaphragm and 37% in M. soleus. The volume of subsarcolemmal mitochondria was almost doubled in each muscle, but the volume of interfibrillar mitochondria did not change significantly. The surface of the inner mitochondrial membranes per unit volume of mitochondrion in M. soleus was significantly increased both in interfibrillar and subsarcolemmal mitochondria, whereas the surface of the outer mitochondrial membranes per unit volume of mitochondrion was increased only in the subsarcolemmal mitochondria. The volume of fat droplets in the diaphragm and M. soleus of cold adapted animals increased significantly by 62% and 150% respectively.     

A morphometric analysis of regional differences in myotomal muscle ultrastructure in the juvenile eel (Anguilla anguilla L.)

Summary Subpopulations of fast and slow fibres within the trunk musculature of elvers were examined using morphometric analysis of electron micrographs. Fibre regions were characterised by their histochemical staining characteristics, and individual fibres located using a coordinate mapping system utilising morphological features as reference points. Percentages of fibre volume occupied by mitochondria, myofibrils, sarcoplasmic reticulum (S.R.), and T-system were determined in each of the fibre groups, along a transect from the skin to the vertebral column (fibres 1–14, respectively).The fine structure of slow (red) fibres (1–2 fibres deep) is relatively homogeneous throughout its range, giving mean values for mitochondria, 21.4%; myofibrils, 61.0%; S.R., 2.10%; T-system, 0.31%. The fibres are relatively small (204 m²) and the mitochondrial cristae poorly developed.In contrast, there is a marked heterogeneity in the ultrastructure of fast (white) fibres, dependent on both position and size. The moderately small (333 m²) superficial fast fibres (3–4 fibres deep) have a significantly higher mitochondrial content (7.6%) than the larger deep fibres (1.2%) (6–12 fibres deep, 775 m²). The mean fractional volumes occupied by myofibrils, S.R., and T-system in the deep fibres are: 80.4%, 5.95%, and 0.38%, respectively. Fibres < 100 m² constitute up to 5% of the fast muscle and have a significantly higher mitochondrial volume (4.3%), more glycogen granules, and a slightly lower volume of S.R. (5.57%) than larger fibres.It is suggested that metabolic subpopulations of fast fibres correspond to different stages of fibre growth. The relatively poorly developed S.R. of eel fast muscle is thought to be correlated with the low frequency, high amplitude nature of the propagated waveform found in anguilliform locomotion.