Ultrastructural and morphometric features of nodal and impulse-conducting cardiac myocytes of the bat Pipistrellus pipistrellus

Cells of the impulse-generating and conducting tissues of the insect-eating bat Pipistrellus pipistrellus were studied and evaluated using ultrastructural morphometry. Sinoatrial node cells are smaller than working atrial cells and measure about 6.5 microm in diameter. Their mitochondira and myofibril content constitute 23% and 19% of cytoplasmic volume, respectively. Corresponding values for working atrial cells are 23% and 52%. Atrioventricular node cells are 4.2 microm in diameter and contain abundant glycogen in the cytoplasm. The fractional volume of mitochondria in about 24% while that of myofibrils is 7%. Cells of the bundle of His are larger (6-8 microm diameter) and contain more cellular organelles than do nodal cells. Their mitochondria and myofibril contents are 25% and 25%, respectively. Cells in the proximal part of the right bundle branch are slender with diameters averaging 3.4 microm. Mitochondrial content is 23% while myofibrils occupy 20% of the cytoplasmic volume of these cells. Distally located bundle branch cells measure 7-10 microm in diameter with mitochondria and myofibril volumes of 30% and 33%. Subendocardial cells in the ventricular free wall are large reaching 28 microm in diameter (cf. 14-18 microm in working ventricular cells) and have mitochondira and myofibril volume fractions of 32% and 29%, respectively (35% & 40% for working ventricular cells).

Morphometric study of specific heart granules in the grey seal (Halichoerus grypus)

Specific heart granules in the grey seal, Halichoerus grypus, a marine mammal, were studied and compared with those in the Wistar rat by ultrastructural morphometry. There is extreme paucity of these granules in atrial cells of the seal, even in the region of the Golgi apparatus, compared with those in the rat. By numerical concentration, granules in the seal are 23 times fewer in number than in the rat. They are also fewer in number than in bats and hamsters for which data is available. The mean (+/-SEM) diameter of heart granules in the seal is significantly less (188 +/- 5.3 nm) than that of the rat (226 +/- 4.6 nm). These observations, the first in a marine mammal, are of interest in relation to the need for conservation of water and electrolytes in pennipids.

Effects of chloroquine and its enantiomers on the development of rat embryos in vitro

The effects of the antimalarial drug chloroquine (CQ) and its enantiomers [(+)-CQ and (-)-CQ] on 9 1/2-day post-implantation rat conceptuses were studied by the whole-embryo culture technique over a 48 hr period. At a concentration of 500 ng/ml of culture medium (0.97 microM), which falls within serum levels attained during long-term CQ therapy, the drugs produced varying degrees of growth retardation and dysmorphogenesis in the conceptuses. These effects were most severe with exposure to racemic CQ (100%) and also to equimolar concentrations of the two enantiomers (90%). Dysmorphogenesis was least with (+)-CQ (30%) and intermediate in severity in those exposed to (-)-CQ (32%). In the CQ and combined enantiomer groups, there was significant reduction in yolk sac diameter to 81% and 73%, the crown-rump length to 77% and 71%, the number of somites to 76% and 74%, and the embryonic protein content to 64% and 49%, respectively, of control values. In the (-)-enantiomer group the only parameter significantly affected was the somite number which was reduced to 83% of control. The growth parameters of (+)-CQ-treated embryos did not differ significantly from controls. The commonest morphological abnormalities observed in all treatment groups were those of axial rotation. Unfused and underdeveloped cranial neural tube, microophthalmia and abnormal otic primordium also occurred frequently, especially in the CQ and enantiomeric combination groups. The results suggest that the commercially available form of chloroquine, CQ, is embryotoxic in doses comparable to serum levels reached during long-term therapy with the drug. It also appears that although the individual enantiomers show minimal embryotoxicity at the dosage used, they potentiate each other's effects in the racemic mixture.

Comparative ultrastructural morphometric analysis of atrial specific granules in the bat, mouse, and rat

Size, incidence, and volume density of atrial specific granules (ASG) in right atrial cells from five animals each of the rat (average weight 210 g), mouse (average weight 28 g), fruit-eating bat Megaloglossus woermanni (BMW; average weight 35 g), and the insect-eating bat Pipistrellus pipistrellus (BPP; average weight 6 g) have been compared via ultrastructural morphometry. In all three parameters of granule measurement, significantly higher figures were obtained in the rodents than in the bats. However, between the rat and the mouse, as also between the two species of bats, no significant differences were noted in any of the measurements. These results therefore do not support the prevalent view that the number and size of the granules decrease with increase in size of the animal species. The low content of ASG in atrial cells of the bats is probably an indication of low demand for the natriuretic hormone of the granule, because, in such animals, and particularly in flight, conservation of fluid and electrolytes is of paramount importance. This suggests that granule content is adapted to fluid and electrolyte regulation in relation to the functional capacity of the animal. We also observed ASG-like structures in endothelial cells of capillaries of bat tissue but not in rodents. The function of these granules or whether or not they represent atrial specific ones is not clear from the present study.

Ultrastructural characteristics of atrial, ventricular and subendocardial (Purkinje) cells of the fruit-eating bat Eidolon helvum

The ultrastructure of the myocardium of the large (285 gm) fruit-eating bat (Eidolon helvum) provides further evidence that, among mammalian species, different types of cardiac myocytes are morphologically heterogeneous. Atrial cells of this species, like those of smaller bats previously studied, have few of the natriuretic hormone-containing granules. These granules are also small, with a mean diameter of 176 +/- 3.9 nm, in comparison with those of the rat (230 +/- 5.8 nm) and mouse (211 +/- 4.7 nm). In all types of myocytes of the bat investigated, mitochondrial matrix granules are more prominent than in those of the rat and mouse. Also distinctive are the Purkinje cells which, aside from their large size (30 microns) and lack of T-tubules, have atrial granule-like inclusions. These cells are well endowed with mitochondria (28% of cytoplasmic volume) and with lipid bodies but have few glycogen granules. Their myofibrillae (33%) are well aligned. The ventricular cells (average diameter 14 microns) have nearly equal volumes of mitochondria (41%) and myofibrils (47%). Mitochondrial cristae, however, are not compactly organized. Lipid material is found in the matrix of the mitochondria. Extensive evaginations of endothelial cells of the bat endocardium appear continuous with endothelial vacuoles. In these endothelial cells, there are also many dense granules of varying shapes and sizes.

Type II corticosteroid receptor-like immunoreactivity in the rat cerebellar cortex: differential regulation by corticosterone

Type II corticosteroid receptor-like immunoreactivity (type II-ir) was localized at the light- and electron-microscopic levels in the rat cerebellar cortex using BUGR2 monoclonal antibody. In intact rats, type II-ir was observed in the nuclei of basket, stellate, Golgi and Purkinje cells. After 1 week of adrenalectomy, type II-ir was barely resolvable in basket, stellate, Golgi and most Purkinje cells. Vermal Purkinje cells showed intense nuclear and cytoplasmic type II-ir. After 4 weeks of adrenalectomy, type II-ir was markedly reduced in most vermal Purkinje cells, however a few in lobules 1-3 and 9 and 10 retained diffuse immunoreactivity. Acute treatment with corticosterone restored nuclear type II-ir to basket, stellate, Golgi and Purkinje cells in the cerebellar hemispheres, flocculi and paraflocculi. In the vermis most Purkinje cells showed nuclear type II-ir following corticosterone treatment. Diffuse type II-ir was, however, retained in a few Purkinje cells in vermal lobules 1-3, 9 and 10. The distribution of GABA-like immunoreactivity (GABA-ir) in the cerebellar cortex was not altered by adrenalectomy or acute corticosterone treatment. 30-60% of type II-ir Purkinje cells in intact rats were GABA-ir. In adrenalectomized and corticosterone-treated rats, a similar proportion of type II-ir Purkinje cells were GABA-ir. The differential regulation of neuronal type II-ir in the cerebellum by corticosterone may account for some of the known effects of glucocorticoids on motor coordination.

Fine structure of subendocardial (Purkinje) cells of the insect-eating bat (Pipistrellus pipistrellus)

Subendocardial cells of the right ventricular myocardium of the West African bat, Pipistrellus pipistrellus, were investigated at the ultrastructural level. The prominent features of these cells include a well-developed T-tubule system and numerous mitochondria with closely packed cristae. Additionally, the cells display large stores of lipid bodies. These unusual features confirm that Purkinje cells are heterogeneous in structural detail. From the paucity and poor structure of myofibrils of these cells, it is likely that the T-tubules may have a primary nutritional role in the regulation of electrolytes in an animal in which the cardiac cycle is particularly rapid. The well-developed mitochondria and the large stores of lipid bodies are appropriate for such active cells in which metabolism is probably of the aerobic type.