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At least 343 records · Page 19Linked to original sources
PubMed1991

Blockage of Na+ currents through poorly selective cation channels in the apical membrane of frog skin and toad urinary bladder.

The blockage of Na+ movements through the poorly selective cation channels in the apical membrane of frog skin (Rana temporaria) and toad urinary bladder (Bufo marinus) was investigated with noise, impedance analysis and microelectrode techniques. Na+ currents through this pathway were studied with NaCl Ringer solutions on both sides. After removal of Ca2+ and other divalent cations from the mucosal compartment, a considerable part of Isc became insensitive to amiloride. In frog skin, the inhibitory effect of amiloride in mucosal Ca(2+)-free solutions was highly variable. In some experiments a complete lack of inhibition was observed. Similarly, in the absence of amiloride, the inhibitory effect of mucosal Ca2+ varied strongly among frogs. In the absence of mucosal Ca2+, analysis of the fluctuation in Isc revealed a Lorentzian component in the power density spectrum. The corner frequency (fc) of this spontaneous Lorentzian was 12.3 Hz in frog skin and 347 Hz in the toad urinary bladder. In frog skin, nanomolar concentrations of mucosal Ca2+ induced an additional Lorentzian noise component. Its corner frequency shifted upwards with increasing mucosal Ca2+ concentration ([Ca2+]m). The relation between 2 pi fc and [Ca2+]m was linear at small [Ca2+]m whereas a parabolic increase of fc was observed at the highest [Ca2+]m. In the bladder, nanomolar concentrations of mucosal Ca2+ did not induce an additional noise component but modified the spontaneous Lorentzian noise by increasing fc proportionally with [Ca2+]m. Microelectrode recordings demonstrated that at least part of the Ca(2+)-blockable current passes through the granulosum cells and confirmed the apical localization of the poorly selective cation channel. The lack of the inhibitory effect of amiloride in Ca(2+)-free solutions seems to originate from the parallel arrangement of the amiloride- and Ca(2+)-blockable pathways and from influences of the blockage of apical channels on the basolateral membrane conductances. The latter cross-talk seems to find its origin in the voltage dependence of the basolateral membrane conductance [Garty H (1984) J Membr Biol 77:213-222; Nagel W (1985) Pflügers Arch 405 [Suppl 1]:S39-S43].

Amiloride↗
PubMed1976

The inhibitory effect of reserpine on the active sodium transport across the frog bladder.

1. The effects of reserpine and harman derivatives on the sodium transport across the frog bladder were examined using a short-circuit current method. The effects of harman derivatives on the Na,K-ATPase activity of the frog kidney were also investigated. 2. Reserpine and harman derivatives inhibited active sodium transport of the frog bladder and their inhibitory effect decreased as reserpine greater than harmine greater than harmaline = harman greater than harmalol. 3. Harman derivatives inhibited Na,K-ATPase activity of the frog kidney. 4. These results suggest that reserpine and harman derivatives inhibit active sodium transport by suppressing the Na,K-ATPase activity of the frog bladder.

Adenosine Triphosphatases↗
PubMed1975

The comparative effects of (Ca2+) and (Mg2+) on on tension generation in the fibers of skinned frog skeletal muscle and mechanically disrupted rat ventricular cardiac muscle.

The effects of intracellular Mg2+ on Ca2+-activated isometric tension generation in rat cardiac muscle fibers and frog skeletal muscle were compared. The membranous sarcolemmal barrier was removed from rat cardiac muscle fibers by mechanical disruption and from frog skeletal muscle by skinning. Tension was recorded in the fibers in bathing solutions of different Ca2+ concentrations and either 5 X 10(-5) M or 1 X 10(-3) M Mg2+ concentration (the same concentrations used in a previous study on single skinned frog skeletal muscle fibers [3]). The amount of Ca2+ required to activate the muscle increased with Mg2+ concentration for both rat ventricular muscle and frog skeletal muscle. These data indicate that intracellular Mg2+ concentration could strongly modulate Ca2+-activated tension in cardiac muscle and that very similar molecular mechanisms are responsible for Ca2+-activated tension in rat ventricular muscle and frog skeletal muscle. The possible sites of action of Mg2+ on Ca2+-activated tension are discussed.

Animals↗
PubMed1994

Effects of dehydration on organ metabolism in the frog Pseudacris crucifer: hyperglycemic responses to dehydration mimic freezing-induced cryoprotectant production.

The metabolic effects of evaporative water loss at 5 degrees C were assessed for both fall- and spring-collected spring peepers Pseudacris crucifer. Frogs readily endured the loss of 50% of total body water. During dehydration organ water content was defined with no change in water content in skeletal muscle, gut, and kidney of 50% dehydrated frogs and reduced water content in liver, brain and heart. Dehydration stimulated a rapid and massive increase in liver glucose production. In fall-collected frogs liver glucose rose by 120-fold to 2690 +/- 400 nmol.mg protein-1 or 220 mumol.g ww-1 in 50% dehydrated frogs and glucose in other organs increased by 2.6- to 60-fold. Spring-collected frogs showed the same qualitative response to dehydration although absolute glucose levels were lower, rising maximally by 8.4-fold in liver. Glucose synthesis was supported by glycogenolysis in liver and changes in the levels of glycolytic intermediates in liver indicated that an inhibitory block at the phosphofructokinase locus during desiccation helped to divert hexose phosphates into the production of glucose. Liver energy status (ATP, total adenylates, energy charge) was maintained even after the loss of 35% of total body water but at 50% dehydration all parameters showed a sharp decline; for example, energy charge fell from about 0.85 to 0.42. Severe dehydration also led to an accumulation of lactate in four organs, probably hypoxia-induced due to impaired circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1980

Sprouting and regression of the nerve at the frog neuromuscular junction in normal conditions and after prolonged paralysis with curare.

A light microscopical, histochemical and electron microscopical investigation of the frog neuromuscular junction has been performed on muscles from animals in different functional states of activity. The combined staining of axon terminals and cholinesterase (ChE) allows a precise description of the nerve terminal arborization and its synaptic contacts. Most terminal arborizations form long continuous contacts with the muscle cell. Distinquishable from these are nerve branches (usually of small diameter)d or distal endings of branches with one or several small and isolated contacts. It is assumed that these are sprouts with newly-formed synaptic sites. Other sprouts end without apparent synaptic contact. At the uttrastructural levet, nerve sprouts end without apparent synaptic contact. At the uttrastructural levet, nerve sprouts growing into empty, well-differentiated synaptic gutters or inducing the formation of new synaptic sites were observed. In other sites, ChE is apparently located at postsynaptic gutters with no nerve present. Similarly, in the electron microscope, well-differentiated synaptic gutters lacking any nerve or Schwann cell elements were observed. In addition, synaptic gutters only partially occupied by the nerve were frequently seen. These features have been interpreted as signs of regression of the nerve terminals. Nerve regression and sprouting were found in animals chronically paralysed with curare over several weeks as well as in untreated frogs (winter and summer frogs, laboratory frogs, fed and unfed). When quantitatively evaluating the occurence of presumed features of nerve sprouting and nerve regression, differences were found between different experimental groups. From this it is concluded that, in addition to developmental changes, the degree of nerve sprouting and regression is controlled by external factors such as muscle activity and seasonal variations. Signs of sprouting and nerve regression can be simultaneously present in a single synapse. It appears that the frog neuromuscular synapse is not a static structure, but is in a state of permenent remodelling.

Acetylcholinesterase↗
PubMed2006

Structural correlates of increased adhesive efficiency with adult size in the toe pads of hylid tree frogs.

Tree frogs are able to climb smooth, vertical substrates using specialised toe pads which adhere via an area-based wet adhesive mechanism. Although the link between pads and arboreality in frogs is well-established, few studies have investigated the influence of morphology on adhesion. Trinidadian tree frogs from the genus Hyla are geometrically similar. There is a tendency towards comparatively reduced mass in larger species, but toe pad area increases as expected with isometry. As adhesion is area-dependent, forces are affected directly by the increase in mass relative to pad area, and there is a decrease in the ability of larger species to adhere to smooth rotation platforms. However, there is an increase in force per unit area that suggests larger species have more efficient toe pads. Toe pad structure is very similar though there are variations in the details of a number of features. Crucially, although differences in morphology appeared small they had demonstrable effects on adhesive efficiency of the pads. Epithelial cell area correlates positively with frog length and adhesive efficiency, related features of cell density and intercellular channel length correlate negatively. These findings are discussed in relation to the different forces involved in the tree frogs' wet adhesive system.

Adaptation, Physiological↗
PubMed1998

Characterization and localization of two forms of gonadotropin-releasing hormone (GnRH) in the spinal cord of the frog Rana ridibunda.

Two molecular variants of gonadotropin-releasing hormone (GnRH) have been previously characterized in the brain of amphibians, i.e., mammalian GnRH (mGnRH) and chicken GnRH-II (cGnRH-II). The aim of the present study was to identify the molecular forms of gonadotropin-releasing hormone and to localize gonadotropin-releasing hormone-containing elements in the spinal cord of the frog Rana ridibunda using highly specific antisera against mGnRH and cGnRH-II. High-performance liquid chromatography (HPLC) analysis combined with radioimmunoassay (RIA) detection revealed that frog spinal cord extracts contained both mGnRH and cGnRH-II. Immunohistochemical labeling revealed that the frog spinal cord was devoid of GnRH-containing cell bodies. In contrast, numerous GnRH-immunoreactive fibers were observed throughout the entire length of the cord. mGnRH immunoreactivity was only detected in the rostral region of the cord and consisted of varicose processes located in the vicinity of the central canal. cGnRH-II-positive fibers were found throughout the spinal cord, the density of immunoreactive processes decreasing gradually toward the caudal region. Two main cGnRH-II-positive fiber tracts with a rostrocaudal orientation were observed: a relatively dense fiber bundle surrounding the central canal, and a more diffuse plexus in the white matter. In addition, short, varicose cGnRH-II-positive processes with a radial orientation were present throughout the gray matter. These fibers were particularly abundant ventromedially and formed a diffuse network that ramified laterally to end in the vicinity of motoneurons. Taken together, these data indicate that the frog spinal cord, like the frog brain, contains two forms of GnRH. The presence of numerous cGnRH-II-immunoreactive fibers in the ventral horn suggests that cGnRH-II may influence the activity of a subpopulation of motoneurons.

Animals↗
PubMed2004

Demographic dynamics of the afro-tropical pig-nosed frog, Hemisus marmoratus: effects of climate and predation on survival and recruitment.

We studied the population ecology of the West African pig-nosed frog, Hemisus marmoratus, to understand the relative contributions of adult survival and recruitment to population growth rate in savannah frogs using mark-recapture modelling. We marked a total of 821 adult frogs over 6 years and recaptured 74 at least once between years. Between-year adult survival was sex-specific and varied between 0.06 and 0.53 for males and 0.07-0.41 for females. Adult survival was significantly associated with annual rainfall and is cause for concern if rainfall declines further in the study region as predicted by changes in the global climate. There was a significant interaction between rainfall and sex with dry weather having a stronger negative effect on males than females. Pig-nosed frogs experienced boom and bust years with a single decline more dramatic than increases. Recruitment (in situ and immigration; 0.67-0.88) was substantially more important than adult survival (0.12-0.33) in determining realised population growth. In situ recruitment was highly variable between years with 1-36% of eggs and tadpoles released by females into the pond surviving to metamorphosis. Years of low tadpole survival were associated with high numbers of predatory tortoises. Thus, like other pond-breeding anurans, pig-nosed frogs showed highly variable juvenile recruitment, low adult survival and density-independent effects on population growth by predators and weather.

Animals↗
PubMed1993

Glossopharyngeal-hypoglossal nerve reflex of the frog in metamorphosis.

In adult frogs, a reflex discharge is elicited from the hypoglossal nerve by mechanical and chemical stimuli to the centre of the tongue surface and electrical stimuli to the glossopharyngeal nerve innervating tongue. However, there has been no report concerning the embryological stage at which this reflex develops. The metamorphosis of a frog is divided into three parts, premetamorphic, metamorphic and climax stage. In the climax stage, the forelimbs are lengthened and the tail gradually shortened. The glossopharyngeal-hypoglossal nerve reflex arose in the early climax stage, during which the tongue appeared on the floor of the mouth. At this stage, the conduction velocities of the first compound action potential of the glossopharyngeal and hypoglossal nerves were about 8.7 and 9.3 m/s, respectively. The latency of the reflex was long, especially the central latency. The response of the glossopharyngeal nerve and the reflex discharge from the hypoglossal nerve upon mechanical stimulation of the tongue were smaller in the tadpole than in the adult frog. As metamorphosis proceeded, the conduction velocity of these nerves increased; the latency shortened, especially the central latency; the reflex response to mechanical stimulus increased. These results suggest that, although the glossopharyngeal-hypoglossal nerve reflex is developed in the early climax stage, it is completed only in the adult frog. Therefore, adult frogs living mainly on land may reject and swallow prey by this reflective tongue movement.

Action Potentials↗
PubMed1989

125I-iodopindolol binding to frog esophageal peptic cells. Detection of amine uptake and beta-adrenergic receptors coupled to pepsinogen secretion.

The beta-adrenergic receptors (beta-ARs) coupled to pepsinogen secretion on frog esophageal peptic cells have been compared to frog erythrocyte beta-ARs using the radioligand 125I-iodopindolol (125I-PIN). 125I-PIN binding to intact peptic cells was time and temperature dependent. Saturation and competition experiments established that a large component of this binding represented radioligand uptake, which was energy dependent, pH sensitive, Na+ independent, and inhibited by agents that depress cellular ATP or disrupt proton gradients. This uptake system, which was absent from frog erythrocytes, appeared similar to that recently described for a number of mammalian cells. 125I-PIN bound to a single class of sites on peptic cell homogenates with a KD = 64 (+/- 5) pM. Binding to cell homogenates and a proportion of the binding to intact cells was inhibited by beta-agonists and antagonists with pharmacological characteristics similar to typical beta 2-ARs of frog erythrocytes. The number of beta-ARs in these peptic cell preparations was 1300 (+/- 240) sites/cell. Isolated peptic cells were poorly responsive to isoproterenol stimulation even in the presence of the phosphodiesterase inhibitor IBMX (3-isobutyl-1-methylxanthine). Pretreatment of cells with the phorbol ester TPA (12-O-tetra-decanoylphorbol-13-acetate) (100 nM) promoted isoproterenol stimulation of pepsinogen secretion. Catecholamine agonists stimulated pepsinogen secretion with an order of potency: isoproterenol greater than epinephrine much greater than norepinephrine, which was identical to that determined for inhibition of 125I-PIN binding. These findings indicate that frog peptic cells contain beta 2-ARs functionally coupled to pepsinogen secretion.

Animals↗
PubMed1978

Glycine high affinity uptake and strychnine binding associated with glycine receptors in the frog central nervous system.

Accumulation of [3H]glycine into synaptosomal fractions occurs by high affinity systems in cerebral cortex, optic tectum, brain stem and spinal cord of the frog. Specific [3H]strychnine binding which appears associated with postsynaptic glycine receptors is also demonstrable in these regions. By contrast, only very low levels of strychnine binding and high affinity glycine uptake occur in higher centers of the rat central nervous system. The relative potencies of small neutral amino acids in competing for [3H]strychnine binding are similar in frog brain and spinal cord. No evidence for a high affinity accumulation of [3H]taurine by synaptosomal fractions of frog spinal cord can be demonstrated. These observations favor glycine rather than taurine as an inhibitory transmitter in frog spinal cord. Moreover, these findings suggest that glycine may have a synaptic role in higher brain centers in the frog.

Animals↗
PubMed1989

Mechanism of the water response in frog gustation: possible significance of surface potential.

The frog taste response to deionized water (water response) after adaptation of the tongue to salts was recorded from the glossopharyngeal nerve under various conditions. It was found that the frog water response exhibits different behavior from the carp water response examined in a previous paper13. (a) The frog water response did not decline during stimulation and lasted for at least 3 min, while the carp water response declined within 10 s after stimulation to a spontaneous level. (b) The frog water response was practically independent of species and concentrations of salts in adapting solutions when the tongue was adapted to salts of monovalent cations, while the carp water response was highly dependent of salt concentration in adapting solution. (c) The water response was increased with an increase of CaCl2 concentration in adapting solution, while it was decreased with an increase of MgCl2 concentration. (d) The water response was suppressed by the presence of electrolytes in stimulating solution: the data obtained with different species of salts were described by a single curve as a function of the ionic strength. (e) The mechanism of the frog water response together with the carp water response was explained in terms of the surface potential.

Action Potentials↗
PubMed1996

Calnexin: its molecular cloning and expression in the liver of the frog, Rana rugosa.

A 2.2-kb cDNA clone encoding the endoplasmic reticulum (ER) resident protein, calnexin (CLX), was isolated from the frog Rana rugosa liver cDNA library and sequenced. The sequence encoded 622 amino acids and was 77% similar to mammalian CLXs and 56% to mouse CLX-t. In the phylogenetic tree, mouse CLX-t was clearly diverged from other CLXs including frog. The amino acid sequence of CLX showed regions similar to those in frog calreticulin (CLT), although CLX, but not CLT, contained a histidine-rich region at the NH2-terminus. CLX gene expression was observed only in the liver among various tissues examined. Additionally, its expression was strong in the liver in 2-month post-metamorphosis frogs, but very weak in adults. The results suggest that the CLX gene is expressed in a tissue- and stage-dependent manner in the frog, R. rugosa, and that CLX is widely distributed in eukaryotic organisms.

Amino Acid Sequence↗
PubMed1983

Immunological characterization of endorphins, adrenocorticotropin, and melanotropins in frog hypothalamus.

To gain more information about the nature and regulation of opiomelanocorticotropic peptides in the frog diencephalon, radioimmunological determinations of alpha- and beta-MSH. ACTH, beta- and gamma-endorphins have been performed in hypothalamic extracts. Sephadex G-50 gel filtration revealed a single peak of alpha-MSH-like immunoreactivity (alpha-MSH-LI) comigrating with synthetic alpha-MSH. Two peaks of ACTH-LI were observed; the major one eluting slightly before human ACTH. Using a porcine beta-endorphin antiserum which exhibited 45% cross-reaction (on a molar basis) with ovine beta-LPH, one major peak of beta-endorphin-LI and two additional components were observed in the elution profile; none of these peaks coeluted with synthetic porcine beta-endorphin. No significant beta-MSH or gamma-endorphin-LI was detected. To investigate a possible role of glucocorticoids on the level of opiomelanocorticotropic peptides in frog hypothalamus, 60 male frogs were treated with dexamethasone (300 micrograms/day) during 8 days. Dexamethasone treatment did not modify the chromatographic distribution and the total amount of alpha-MSH-LI and ACTH-LI in hypothalamic extracts. A slight (15%) increase in beta-endorphin-LI was even observed after 8 days of dexamethasone treatment. From these results it is concluded that three classes of opiomelanocorticotropic peptides are present in the frog hypothalamus in the following order of concentration: beta-endorphin-LI greater than alpha-MSH greater than ACTH. In addition, circulating glucocorticoids which significantly reduce the concentration of opiomelanocorticotropic hormones in the distal lobe of the frog pituitary (S. Jégou, M. C. Tonon, F. Leboulenger, C. Delarue, J. Côté, G. Pelletier, and H. Vaudry (1981a). In "Adv. Physiol. Sci.' E. Stark, G. B. Makara, Zs. Acs, and E. Endröczi, eds., Vol. 13, pp. 129-133. Pergamon, Budapest.) do not modify the amount of these peptides in the hypothalamus.

Adrenocorticotropic Hormone↗
PubMed1986

Effect of melatonin on oocyte growth and recruitment, hypophyseal gonadotrophs, and oviduct of the frog Rana cyanophlyctis maintained under natural photoperiod during the prebreeding phase.

The effect of 25 and 50 micrograms melatonin on oocyte growth and recruitment, hypophyseal gonadotrophs, and oviduct was studied in Rana cyanophlyctis maintained under natural photoperiod (12.36 L/11.24 D) during the prebreeding phase (April). During the experiment minimum and maximum temperature was 20 +/- 0.2 degrees and 37.2 +/- 0.3 degrees, respectively; the daily fluctuation between these was 17 +/- 0.4 degrees. Melatonin was injected (ip) 6 days a week for 31 days and frogs were killed on the 32nd day. Treatment with 25 or 50 micrograms melatonin 2 hr after the beginning of natural photophase had no effect on the gonadosomatic index (GSI) or on the percentage and number of oocytes at each stage of development. Injections 7 hr after the beginning of the natural photophase caused a marked decrease in the percentage of medium second growth phase (MSGP) and large second growth phase (LSGP) oocytes, while the percentage of the first growth phase (FGP) oocytes increased. However, in 50% of the 25 micrograms and 62.5% of the 50 micrograms melatonin-injected frogs, there was significant reduction in the number of both MSGP and LSGP oocytes. Frogs which received melatonin (25 and 50 micrograms) 11 hr after the onset of natural photophase exhibited a significant (P less than 0.05) decrease in the number of MSGP and LSGP oocytes and GSI. Atretic follicles (AF) increased in all the melatonin-treated groups, but a significant increase was seen only in evening-injected frogs receiving 50 micrograms melatonin. The mean diameter of the largest oocytes decreased significantly in 50 micrograms melatonin-injected frogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Comparative effects of corticotropin-releasing factor, arginine vasopressin, and related neuropeptides on the secretion of ACTH and alpha-MSH by frog anterior pituitary cells and neurointermediate lobes in vitro.

The ability of corticoliberin (CRF), urotensin I, sauvagine, arginine-vasopressin (AVP), and mesotocin to stimulate ACTH release by frog anterior pituitary cells and alpha-melanotropin (MSH) by frog neurointermediate lobe was studied in vitro using a perifusion technique. CRF and AVP were found to be potent stimulators of ACTH secretion, whereas urotensin I and sauvagine were totally inactive. In opposition to recent findings in the rat. CRF did not modify alpha-MSH secretion by the frog neurointermediate lobe. Mesotocin, which is present in the parenchymal cells of the frog pars intermedia, had no effect on alpha-MSH release in vitro. No potentiation of CRF-induced ACTH release was observed when anterior pituitary cells were incubated with a combination of AVP and CRF. Together with the recent elucidation of a CRF-like molecule in the frog diencephalon, these results suggest that, in Amphibia, CRF and AVP exert their stimulatory action specifically on distal lobe corticotrophs.

Adrenocorticotropic Hormone↗
PubMed1992

Microvascular flow response to localized application of norepinephrine on capillaries in rat and frog skeletal muscle.

Recently, Dietrich (1989, Microvasc. Res. 38, 125-135) demonstrated that a local application of a minute amount of norepinephrine (NE, 5.5 mM, 0.01-88 pmole) on a capillary in rat mesentery can elicit constriction of the feeding arteriole 0.5-1.0 mm away. This constriction can reduce or even stop blood flow in capillaries supplied by the arteriole. The main objective here was to show that the phenomenon of reduced flow occurs not only in the rat mesentery but also in other tissues and species. We chose to study the rat tibialis anterior and frog sartorius muscles. Using the same intravital video-microscopic approach as in the mesentery, strong NE stimuli (3 mM) were applied iontophoretically 48 times to 19 capillaries in 10 rats anesthetized with pentobarbital. They resulted in significant reductions (average: 80%) of the red blood cell velocity (VRBC) in capillaries. The onset of these reductions (i.e., 10% decrease from control) occurred within 3-52 sec (average: 20.9 sec) from the time of NE application. Reductions lasted 6.0 min. The same stimuli were applied 42 times to 15 capillaries in 6 frogs anesthetized with urethane. The average VRBC reduction was 86%. The onset occurred within 30.6 sec while the reduction lasted 6.6 min. Under the same conditions, arteriolar diameters in the sartorius muscle decreased significantly from 28.5 to 22.5 microns (n = 8). We also used local microinjection of small droplets of NE (30 mM) to 13 capillaries in 7 frogs. This resulted in a significant VRBC reduction of 64% with an onset time of 44.2 sec and a reduction duration of 17.2 min. Weak NE stimuli (3 microM) applied iontophoretically to 10 capillaries in 5 frogs resulted in marginal, but significant, VRBC reductions (9%). The present study demonstrates that the phenomenon of reduced flow after local application of NE may be a general phenomenon as it occurs also in skeletal muscle in both rat and frog. Our accompanying paper addresses the hypothesis that the phenomenon reflects communication of a NE-induced signal along the capillary.

Animals↗
PubMed1984

Comparative stereology of the lizard and frog myocardium.

The atria and ventricles of the frog and lizard were quantitated using stereologic techniques. The volume fraction (Vv) and surface density (Sv) of the free, junctional and total sarcoplasmic reticulum and mitochondria of the lizard atrium and ventricle were greater than in the corresponding chambers in the frog. Myofibrillar volume fraction and plasmalemmal surface density did not differ between the two species. The volume fraction and surface density of the free and total SR, and myocardial granules were greater in the lizard atrium than ventricle but the myofibrillar Vv and mitochondrial Vv and Sv were less. The Sv of the free SR, total SR, and the Vv and Sv of myocardial granules of the frog atrium were greater than in the frog ventricle. There were no differences between myofibrils and mitochondria in the frog atrium and ventricle.

Anatomy, Comparative↗