Nonenzymatic separation of myocardial cell nuclei from whole heart tissue

Extracellular matrix formation by epithelial cells from human polycystic kidney cysts in culture

Cells from the cysts of patients with autosomal dominant polycystic kidney disease (PKD) were grown in vitro under standard conditions without the aid of collagen-pretreated surfaces, and both the synthesis and composition of the extracellular matrix were investigated. At confluence, PKD cells presented the typical features of epithelial cells, but showed a different collagen composition from fibroblasts. Compared with normal tubular epithelia (NTE), PKD monolayers produced an excess of extracellular matrix, which accounted for 30% of the total incorporation of [3H] proline, although this value was considerably lower (by a factor of 10) in the case of NTE. Immunohistochemical and electrophoretic techniques revealed a complex collagen composition in the extracellular matrix which included [alpha (III)]3 and collagen IV. However, part of the collagen components remained unidentified in spite of the fact that they exhibited a typical M(r) of alpha 1(I) and alpha 2(I) in the presence of urea. Immunoprecipitation with monospecific antibodies and Northern blotting with specific probes failed to recognize alpha 1(I) and alpha 2(I), but demonstrated their presence in fibroblasts. Purification and cyanogen bromide digestion demonstrated a strong interhomology in fingerprint peptide composition among the uncharacterized collagens synthesized by PKD cells, thus suggesting a common identity. These observations document a markedly augmented production of extracellular matrix by PKD cultured cells in vitro, and show the presence of collagens which do not share homologies with the major collagen molecules. A better characterization of extracellular matrix composition is central to any comprehension of the cytogenetic mechanisms in vivo.

Generation of reentry in anisotropic myocardium

INTRODUCTION

We investigated numerically the effects of the rotation of fiber axis orientation through the myocardial wall on wave propagation.

METHODS AND RESULTS

We show that because of this rotation and inherent discrete properties of myocardium, a premature stimulus can create unidirectional conduction block leading to reentry.

CONCLUSION

The dynamics of the subsequent reentrant patterns are complicated by the presence of rotational anisotropy, as the center of reentry drifts, and the reentry terminates in finite time when it collides with the domain boundary.

The secretion of fluid by renal cysts from patients with autosomal dominant polycystic kidney disease

BACKGROUND

The mechanism by which fluid accumulates in renal cysts of adults with autosomal dominant polycystic kidney disease is not known. This study was designed to determine whether transepithelial secretion of fluid may account for this accumulation.

METHODS

We studied in vitro intact cysts that were excised from kidneys removed from three patients with end-stage autosomal dominant polycystic kidney disease. The cysts were loaded with natural cyst fluid or with a combination of Dulbecco's modified Eagle's medium and Ham's F12 medium (DME-F12) and incubated in DME-F12 for 24 hours. Fluid secretion, determined by the change in the weight of the cysts, was expressed as the rate of fluid secretion per square centimeter of surface area per 24 hours, to correct for the wide variation in the sizes of the cysts. To test for endogenous secretagogues, cyst fluid was added to confluent monolayer cultures of canine- and human-kidney cells.

RESULTS

During the first 24 hours of incubation, the mean (+/- SE) rate of fluid secretion in nine cysts containing natural cyst fluid was 20.8 +/- 5.6 microliters per square centimeter of surface area per 24 hours, as compared with 2.3 +/- 3.6 microliters per square centimeter per 24 hours in nine cysts containing incubation medium. Each group of cysts was then incubated with forskolin, a nonspecific stimulator of adenylate cyclase activity, for an additional 24 hours. During this period the fluid-secretion rate of cysts containing natural cyst fluid did not change; however, the secretion rate of those containing incubation medium increased to 9.1 +/- 4.4 microliters per square centimeter per 24 hours (mean change, 6.8 +/- 1.1; P < 0.001). Cyst fluid stimulated fluid secretion by polarized monolayers of canine- and human-kidney cells.

CONCLUSIONS

Renal cysts from patients with autosomal dominant polycystic kidney disease can secrete fluid, and net fluid secretion can be increased by unidentified secretagogues in the cyst fluid. These results suggest that the process of cyst enlargement may be susceptible to pharmacologic intervention.

Spread of excitation in a myocardial volume: simulation studies in a model of anisotropic ventricular muscle activated by point stimulation

INTRODUCTION

The purpose of this study was to present simulations of excitation wavefronts spreading through a parallelepipedal slab of ventricular tissue measuring 6.5 x 6.5 x 1.0 cm.

METHODS AND RESULTS

The slab incorporates the anisotropic properties of the myocardium including the transmural counterclockwise fiber rotation from epicardium to endocardium. Simulations were based on an eikonal model that determines excitation times throughout the ventricular wall, which is represented as an anisotropic bidomain. Excitation was initiated by delivering ectopic stimuli at various intramural depths. We also investigated the effect of a simplified Purkinje network on excitation patterns. Excitation wavefronts in the plane of pacing, parallel to epicardial-endocardial surfaces, were oblong with the major axis approximately oriented along the local fiber direction, with bulges and deformations due to attraction from rotating fibers in adjacent planes. The oblong intersections of the wavefront with planes at increasing distance from pacing plane rotated clockwise or counterclockwise, depending on pacing depth, but wavefront rotation was always less than fiber rotation in the same plane. For all pacing depths, excitation returned toward the plane of pacing. Return occurred in multiple, varying sectors of the slab depending on pacing depth, and was observed as close as 6 mm to the pacing site.

CONCLUSION

Curvature of wavefronts and collision with boundaries of slab markedly affected local velocities. Shape and separation of epicardial isochrones and spatial distribution of epicardial velocities varied as a function of site and depth of pacing. When the Purkinje network was added to the model, epicardial velocities revealed the subendocardial location of the Purkinje-myocardial junctions. Considerable insight into intramural events could be obtained from epicardial isochrones. If validated experimentally, results may be applicable to epicardial isochrones recorded at surgery.

Sodium channel blockade enhances dispersion of the cardiac action potential duration. A computer simulation study

The goal of this study was to elucidate the causes why the proarrhythmic activity of sodium channel blocking drugs is enhanced during the post-infarction period. Therefore, we studied the effects of a reduction in sodium conductance on the action potential duration and its dispersion in a simulated array of 1600 ventricular myocytes. Cardiac tissue is known to possess anisotropic properties with regard to the intercellular electrical resistances (R). Infarction as well as aging causes deposition of collagen in the cardiac tissue, thereby inducing zones of high electrical resistance leading to a non-uniform anisotropy (Spach et al., Circ Res 62:811, 1988). For our study an array of 40*40 ventricular myocytes was simulated using Beeler-Reuter-algorithms. Physical tissue properties were assumed to be either a) uniform anisotropic (i.e., all longitudinal R = 5000 omega cm, all transversal R = 20,000 omega cm; UA) or b) non-uniform anisotropic (i.e., transversal R for the inner 10*10 cells was set to 10(10) omega cm; NUA). Mean action potential duration (APD) was increased under UA (287 ms. dispersion: 0.8 ms) when compared to NUA (285 ms, disp.: 3.2 ms). Assuming a 25% decrease in sodium conductance, we found the total activation time (TAT) to be increased (from 99 to 139 ms), indicating slowing of conduction, APD to be shortened (from 287 to 259 ms), and the APD-dispersion to be increased (from 0.8 to 29 ms) in UA. These changes were more pronounced in the case of NUA: increase in TAT from 103 to 150 ms, APD-shortening from 285 to 214 ms and a marked increase in APD-Dispersion from 3.2 to 53 ms). From these results it is concluded that a) the effects of a reduced sodium conductance are more pronounced in NUA tissue, and b) that the resulting increase in dispersion may provoke arrhythmia by local differences in APD. This may be one of the mechanisms underlying the increased proarrhythmic risk of class I antiarrhythmic drugs in the postinfarction period.

Glibenclamide partly reverses monesin inhibition of insulin secretion, in vivo

Glibenclamide, a second generation sulfonylurea, is an oral hypoglycemic drug. It seems to act mainly on the ATP-driven K(+)- channels of the beta-cells of pancreas determining insulin secretion. Because monensin, a Na+/H+ antiport, is able when administered to rats in vivo to inhibit insulin secretion, the action of glibenclamide is studied on glycemia and insulinemia to verify if it can antagonize the action of monensin. The results show that glibenclamide is able to partly reverse ionophore induced hyperglycemia and the inhibition of insulin secretion. These results might be interpreted as if glibenclamide only reverses the ATP-driven K(+)- channel dependent insulin secretion. Moreover the antagonist action of glibenclamide is slightly delayed when both drugs are administered together. The role of Na+/H+ antiport in basal insulin secretion is discussed.

Cellular automation model of ventricular conduction

A computer simulation of ventricular conduction is presented with a discrete element ventricular conduction model. The model is shown to be capable of demonstrating normal ventricular rhythm, including QRS and T-waves, plus a variety of rhythm disturbances including missed beats, electrical alternans and self-sustaining instability with arrhythmias. The morphology of the range of alternans produced bears a strong resemblance to certain clinically recognised arrhythmias.

Actin and myosin genes are transcriptionally regulated during mouse skeletal muscle development

During primary and secondary myotube formation in utero and subsequent maturation of muscle fibers after birth there are complex changes in the pattern of contractile protein gene expression at the RNA and protein levels. In order to determine the degree of transcriptional regulation of actin and myosin genes we have carried out "nuclear run-on" experiments using nuclei prepared from the limb muscle of mice at 14.5, 15.5, 17.5, and 18.5 days in utero and at 10-12 and 12.5 days after birth. We show that transitions in the expression of these genes in vivo are regulated transcriptionally. Transcription of the sarcomeric alpha-actins changes from cardiac to predominantly skeletal actin over this time period; transcription of the beta-actin gene is repressed. The myosin heavy chain and myosin light chain genes also undergo transcriptional transitions during muscle development. Notably, transcription from the MLC3F promoter is activated after that of the MLC1F promoter, which is part of the same gene. These results are discussed in the context of published RNA data.

Effect of monensin on insulin and glucose concentration in rat serum

The effect of monensin, an electroneutral ionophore that exchanges Na+ for H+, is investigated on glucose and insulin concentration in serum of female rats. After monensin administration hyperglycemia is observed. Hyperglycemia is concentration and time dependent. In fact serum glucose starts increasing with 0.5 mg/kg b.w. of monensin and increases sharply till 2.5-3.0 mg/kg b.w. The timing of the appearance shows an increase already after few minutes and keeps increasing reaching its maximum between 30-120 minutes. Hyperglycemia is reversed by insulin; if not treated spontaneously it returns to normality in 4-5 hours. An inverse correlation is observed between insulinemia and glycemia. A significant fall in serum insulin concentration can be observed, with or without glucose-stimulation of insulin release, already after five minutes of treatment. Insulinemia returns to normal values after about two hours. The action of monensin on glycemia might therefore be a reversible inhibition of insulin secretion by the beta-cells of the pancreas.

An eikonal-curvature equation for action potential propagation in myocardium

We derive an "eikonal-curvature" equation to describe the propagation of action potential wavefronts in myocardium. This equation is used to study the effects of fiber orientation on propagation in the myocardial wall. There are significant computational advantages to the use of an eikonal-curvature equation over a full ionic model of action potential spread. With this model, it is shown that the experimentally observed misalignment of spreading action potential "ellipses" from fiber orientation in level myocardial surfaces is adequately explained by the rotation of fiber orientation through the myocardial wall. Additionally, it is shown that apparently high propagation velocities on the epicardial and endocardial surfaces are the result of propagation into the midwall region and acceleration along midwall fibers before reemergence at an outer surface at a time preceding what could be accomplished with propagation along the surface alone.

Na+/H+ exchange is responsible for intracellular pH regulation in insulin-secreting HIT-T15 cells

The addition of glucose to suspensions of HIT-T15 insulinoma cells caused a small, transient acidification followed by a gradual, progressive alkalinisation, as assessed by the fluorescent pH-sensitive dye 2',7'-biscarboxyethyl-5'-(6')-carboxyfluorescein (BCECF). Treatment of cells with acetate or lactate produced an immediate, marked acidification followed by recovery and a subsequent alkalinisation. In contrast, addition of NH4Cl caused a rapid rise in intracellular pH (pHi) and recovery to resting values. In cells where Na+/H+ exchange was inhibited, either with amiloride or by omission of Na+ from the medium, glucose caused a progressive acidification, whilst recovery from acetate- or lactate-induced acidification was prevented. Under sodium-free conditions, recovery from acidification could be initiated by addition of Na+. Inhibition of HCO3-/Cl- exchange by pretreatment with 4,4'-diisothiocyanatostilbene 2,2'-disulphonic acid (DIDS), or by omission of HCO3- or Cl- from the medium did not affect any of the changes in pHi elicited by the above agents. It is concluded that the principal mechanism responsible for pHi regulation in HIT-T15 cells is the Na+/H+ antiporter and that the HCO3-/Cl- exchange systems make little, if any, contribution.

The calmodulin-activated form of the Ca2(+)-pumping ATPase of the cardiac sarcolemmal membrane produces Ca2+ gradients with a thermodynamic efficiency of 100%

The thermodynamic efficiency of the calmodulin-activated form of the Ca2+-pumping ATPase of the bovine cardiac sarcolemma (SL) was evaluated in sealed vesicles under reversible conditions. The free internal Ca2+ concentration ([Ca2+]i) established in the SL vesicle lumen by action of the ATPase was determined as a function of the [ATP]/([ADP][Pi]) ratio for the following experimental conditions: 250 mM sucrose, 100 mM KCl, 0.1 mM Mg2+, 25 mM HEPES, 25 mM Tris, pH 7.40, at 37 degrees C, [Ca2+]o = 50 nM (1 mM Ca/EGTA buffer), 0.75 mM Mg-ATP, 0.1 mM Pi, variable [ADP]. Under these conditions, with the pump working near its Km of 64 nM, the [Ca2+]i achieved was less than or equal to 18 mM, decreasing with increasing [ADP] for [ADP] greater than or equal to 0.84 mM. A plot of the square of the [Ca2+]i/[Ca2+]o ratio against [ATP]/([ADP][Pi]) gave a straight line with a slope of 1.5 x 10(7) M. This was in agreement, within the experimental error, with the equilibrium constant for ATP hydrolysis under these conditions (1.09 x 10(7) M). These results demonstrate (1) tight coupling between Ca2+ transport and ATP hydrolysis with a stoichiometry of 2 Ca2+ moved per ATP split and (2) a low degree of passive leakage. Analysis at low [ADP] (less than 0.83 mM) showed the unexpected result that ADP increases the rate of the forward reaction of the pump. The maximal effect on the initial rate is a 96 +/- 5% increase, with an EC50 of approximately 0.4 mM (ADP). Similar but lesser stimulation was observed with CDP. The implications of the above results for the energetics of the pump and for its physiological function in the beating heart are discussed.

Wavefront propagation in an activation model of the anisotropic cardiac tissue: asymptotic analysis and numerical simulations

In this paper we present a macroscopic model of the excitation process in the myocardium. The composite and anisotropic structure of the cardiac tissue is represented by a bidomain, i.e. a set of two coupled anisotropic media. The model is characterized by a non linear system of two partial differential equations of parabolic and elliptic type. A singular perturbation analysis is carried out to investigate the cardiac potential field and the structure of the moving excitation wavefront. As a consequence the cardiac current sources are approximated by an oblique dipole layer structure and the motion of the wavefront is described by eikonal equations. Finally numerical simulations are carried out in order to analyze some complex phenomena related to the spreading of the wavefront, like the front-front or front-wall collision. The results yielded by the excitation model and the eikonal equations are compared.

Regulation of pH in individual pancreatic beta-cells as evaluated by fluorescence ratio microscopy

Pancreatic beta-cells are known to maintain intracellular pH (pHi) at a value well above that predicted from the electrochemical gradient. The mechanisms for the active extrusion of protons were examined by continuously monitoring pHi in individual beta-cells from ob/ob mice using the fluorescent indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). In a medium nominally devoid of bicarbonate, the steady-state pHi was 6.82 +/- 0.02 and the intracellular buffering capacity was equivalent to 79 +/- 3 mM/pH unit. pHi remained unaffected after raising the glucose concentration from 3 to 20 mM, it was lowered when depolarizing the beta-cells with tolbutamide and it increased in the presence of carbachol. After removal of Na+ there was a significant drop of pHi and blockage of the pHi recovery following acid loading with the NH4+ prepulse technique. Whereas addition of amiloride had a similar, but less pronounced effect, omission of Cl- resulted in moderate alkalinisation. After switching to a medium containing bicarbonate, minor acidification was followed by adjustment of pHi to a steady state higher than the initial one. The results indicate that the acid load arising from glucose metabolism in the beta-cells is effectively buffered and the protons extruded both by Na+-H+ and Cl- -HCO3- exchangers.

Characterization of inositol 1,4,5-trisphosphate-sensitive (IsCaP) and -insensitive (IisCaP) nonmitochondrial Ca2+ pools in rat pancreatic acinar cells

We have measured Ca2+ uptake and Ca2+ release in isolated permeabilized pancreatic acinar cells and in isolated membrane vesicles of endoplasmic reticulum prepared from these cells. Ca2+ uptake into cells was monitored with a Ca2+ electrode, whereas Ca2+ uptake into membrane vesicles was measured with 45Ca2+. Using inhibitors of known action, such as the H+ ATPase inhibitors NBD-Cl and NEM, the Ca2+ ATPase inhibitor vanadate as well as the second messenger inositol 1,4,5-trisphosphate (IP3) and its analog inositol 1,4,5-trisphosphorothioate (IPS3), we could functionally differentiate two nonmitochondrial Ca2+ pools. Ca2+ uptake into the IP3-sensitive Ca2+ pool (IsCaP) occurs by a MgATP-dependent Ca2+ uptake mechanism that exchanges Ca2+ for H+ ions. In the absence of ATP Ca2+ uptake can occur to some extent at the expense of an H+ gradient that is established by a vacuolar-type MgATP-dependent H+ pump present in the same organelle. The other Ca2+ pool takes up Ca2+ by a vanadate-sensitive Ca2+ ATPase and is insensitive to IP3 (IisCaP). The IsCaP is filled at "higher" Ca2+ concentrations (approximately 10(-6) mol/liter) which may occur during stimulation. The low steady-state [Ca2+] of approximately 10(-7) mol/liter is adjusted by the IisCaP. It is speculated that both Ca2+ pools can communicate with each other, the possible mechanism of which, however, is at present unknown.

Effect of extracellular sodium removal upon 86Rb outflow from pancreatic islet cells

The present study was undertaken to characterize the effect of extracellular Na+ removal on 86Rb outflow from perifused rat pancreatic islets. Complete Na+ omission inhibited 86Rb outflow whether the islets were perifused in the presence or in the absence of extracellular Ca2+. Ouabain (1 mM) did not reduce the inhibitory effect of Na+ deprivation, whilst diphenylhydantoin (72.9 microM) mimicked the Na+-removal-induced fall in 86Rb outflow. Glucose (16.7 mM) lost its capacity to inhibit 86Rb outflow when the perifusate was deprived of extracellular Na+. These results indicate that Na+ omission reproduces the inhibitory effect of glucose on 86Rb outflow. The reduction in 86Rb outflow recorded after Na+ deprivation could be mediated by an intracellular acidification and/or a decrease in the intracellular Na+ activity. It is tempting to speculate that the capacity of glucose to reduce the B-cell Na+ content may participate in the process by which the sugar decreases K+ permeability.

RNA transcription in myocardial-cell nuclei during postnatal development. A study establishing an assay system for transcription in vitro

A system for RNA transcription in vitro was established in order to determine the relative rate of RNA synthesis in neonatal and adult rat myocardial cells. This assay system optimizes the incorporation of [3H]UMP into RNA by using 3.5 x 10(7) myocardial-cell nuclei, and minimizes RNA degradation for at least 1 h in transcription in vitro, by the addition of human placental RNAase inhibitor. A 100% increase in the incorporation of [3H]UMP into myocardial-cell RNA was found on addition of this inhibitor. Myocardial-cell nuclei derived from 5-, 10-, 15-, 20-, and greater than 100-day-old rat hearts indicated that there is a progressive decrease in RNA synthesis with age. A 3-fold increase in RNA synthesis in 5-day-old myocardial cell nuclei as compared with 20-day-old rat heart was found. RNA synthesis in the adult myocardial cell nuclei decreased more than 10-fold in comparison with the 5-day-old newborn. The incorporation of [3H]UMP into rat liver nuclear RNA was 3-fold greater than in the myocardial-cell nuclear RNA, even when compared with the highly active transcription of 12-day-old heart nuclei. In order to determine the relationship between total RNA synthesis and the extent of specific gene expression in myocardial-cell nuclei during development, two distinct cDNA probes were used for Northern-blot analysis. Our results indicate that myosin-heavy-chain gene expression is remarkably decreased with age, whereas the 'housekeeping' gene is continually expressed independently of age.

Catecholamines, calcium and cardiomyopathy

The cardiomyopathic Syrian hamster has a genetically transmitted form of dilated cardiomyopathy and is an important paradigm of myocardial disease, particularly for studies addressing the earliest stages of myocardial dysfunction. This model exhibits an increase in cardiac sympathetic tone in the presence of an altered expression of sarcolemmal calcium channels or of alpha 1 receptors, and a defective handling of calcium by both cardiomyocytes and vascular smooth muscle cells. Increased expression of the oncogene c-myc is evident in cardiomyocytes before any overt evidence of heart disease. Alterations in a nuclear phosphoprotein, which appears to be important in the regulation of gene expression, have also been identified. The disease becomes phenotypically manifest by the development of microvascular spasm, reperfusion injury and myocyte loss. Myocyte loss, in turn, burdens the remaining cells with an increasing load, increasing sympathetic stimulation, myocyte hypertrophy and further cell loss--a continuing vicious spiral that culminates in the development of myocardial failure. All of the features of hamster cardiomyopathy may be prevented by the administration of verapamil or prazosin to juvenile hamsters before the phenotypic onset of their heart disease. This understanding has led to the study of new imaging agents that promise the detection of such forms of cardiomyopathy in their earliest stages and a means by which the effects of therapy can be assessed. If such mechanisms are applicable to human cardiomyopathy, early treatment of patients with adrenergic antagonists or calcium antagonists should be beneficial.

Nuclear thyroid hormone receptors in rabbit heart: reduced triiodothyronine binding in atrium compared with ventricle

Radiolabeled triiodothyronine (T3) binding to isolated nuclei was measured to compare the binding characteristics of the nuclear receptors in rabbit ventricular and atrial muscle cells. Scatchard analysis of the binding data yielded a maximum binding capacity of 170 +/- 20 fmol per mg DNA and apparent dissociation constant of 525 +/- 100 pM for ventricular nuclei. The binding capacity and the dissociation constant for the atrial muscle cell nuclei were 55 +/- 10 fmol per mg DNA and 500 +/- 75 pM, respectively. The results suggest that the binding capacity for T3 receptor in the atrium is considerably lower than that found in the ventricle. The reduced binding capacity of the T3 receptor in the atrium might reflect differences in the nuclear T3 receptors between ventricle and atrium.

Effects of acute sodium omission on insulin release, ionic flux and membrane potential in mouse pancreatic B-cells

The effects of acute omission of extracellular Na+ on pancreatic B-cell function were studied in mouse islets, using choline and lithium salts as impermeant and permeant substitutes, respectively. In the absence of glucose, choline substitution for Na+ hyperpolarized the B-cell membrane, inhibited 86Rb+ and 45Ca2+ efflux, but did not affect insulin release. In contrast, Li+ substitution for Na+ depolarized the B-cell membrane and caused a Ca2+-independent, transient acceleration of 45Ca2+ efflux and insulin release. Na+ replacement by choline in the presence of 10 mM glucose and 2.5 mM Ca2+ again rapidly hyperpolarized the B-cell membrane. This hyperpolarization was then followed by a phase of depolarization with continuous spike activity, before long slow waves of the membrane potential resumed. Under these conditions, 86Rb+ efflux first decreased before accelerating, concomitantly with marked and parallel increases in 45Ca2+ efflux and insulin release. In the absence of Ca2+, 45Ca2+ and 86Rb+ efflux were inhibited and insulin release was unaffected by choline substitution for Na+. Na+ replacement by Li+ in the presence of 10 mM glucose rapidly depolarized the B-cell membrane, caused an intense continuous spike activity, and accelerated 45Ca2+ efflux, 86Rb+ efflux and insulin release. In the absence of extracellular Ca2+, Li+ still caused a rapid but transient increase in 45Ca2+ and 86Rb+ efflux and in insulin release. Although not indispensable for insulin release, Na+ plays an important regulatory role in stimulus-secretion coupling by modulating, among others, membrane potential and ionic fluxes in B-cells.

Congenital murine polycystic kidney disease. II. Pathogenesis of tubular cyst formation

In the current study, the pathogenesis of proximal tubular cyst formation was studied in an animal model of polycystic kidney disease, the CPK mouse. The specific roles of (a) sodium-potassium adenosine triphosphatase (Na-K ATPase) activity, determined by an enzyme-linked kinetic microassay, (b) proximal tubular epithelial hyperplasia, determined by calculation of mitotic indices, and (c) altered proximal tubular basal lamina formation, determined by immunohistological localization of basal lamina glycoproteins, were investigated at progressive developmental stages of CPK proximal tubular cyst formation. Increases in renal Na-K ATPase were present at the earliest fetal stages of proximal tubular cyst formation, and subsequently paralleled the course of proximal tubular cyst progression. Proximal tubular epithelial hyperplasia, although not present at the earliest stages of cyst formation, was a consistent feature of progressive proximal tubular cystic enlargement. Abnormalities in basal lamina glycoprotein expression were not present at any stage of proximal tubular cyst development. We conclude that increased Na-K ATPase and tubular epithelial hyperplasia are significant features of proximal tubular cyst formation in the CPK mouse.

Morphologic differences of the endocardial electrogram in beats of sinus and ventricular origin

The lack of accurate arrhythmia detection and identification is one of the major obstacles to improvement in the efficacy of antitachycardia devices. We evaluated a method for detection of beats of ventricular origin compared to sinus rhythm based on the morphology of the endocardial electrogram. In order to compare mechanically induced ventricular beats to normal sinus beats, endocardial electrograms from a standard pacing electrode were recorded from eight open-chested dogs. Time and frequency domain features analyzed included peak-to-peak amplitude (AMP), maximal slew rate (dV/dT), and frequency content (-3 dB downpoint). Quantitative morphologic comparison of the waveforms was performed using standard correlation and by the absolute area of difference between the waveform and a sinus beat template. The AMP and dV/dT for a group of ventricular beats did not differ significantly from beats of sinus origin. In the unipolar configuration -3 dB for ventricular beats was significantly different from sinus beats (p = .01), but overlap occurred in three of eight cases. Conversely, using either method of assessment of morphological differences, all ventricular beats could be identified without overlapping the values for normal beats. We concluded that morphologic analysis of the endocardial electrogram by such methods may be a highly accurate means of distinguishing between beats of sinus and ventricular origins. This technique may also be applicable to the problem of automatic rhythm identification by implanted devices.

On the formation of circulating patterns of excitation in anisotropic excitable media

We present a model of excitable media with the feature that it has a vulnerable phase during which a premature current stimulus will result in the formation of a reentrant self-sustained wave of excitation. The model exploits anisotropic coupling of identical cells, and is therefore useful as a model for the myocardium. We give rigorous verification that there is a vulnerable phase, and demonstrate numerically that permanently rotating waves are formed. Finally, it is shown that the direction of fastest propagation in myocardium is not necessarily the direction of highest safety factor, contrary to commonly accepted opinion.

The effect of inactivation of calcium channels by intracellular Ca2+ ions in the bursting pancreatic beta-cells

Based on recently determined ionic channel properties, a simple theoretical model for the burst activity of the pancreatic beta-cell is formulated in this paper. The model contains an inward voltage-activated Ca2+ current which is inactivated by intracellular calcium ions and an outward K+ current that is activated by the membrane potential. The probability of opening of the channel gates is represented by Boltzmann equations. Our model is applicable in a regime where an ATP-blockable K+ channel is inhibited. In this regime, glucose is treated as an activator for the rate of efflux of intracellular Ca2+ ions, and hence its effect is equated to kca, the efflux rate constant. In addition, intracellular H+ ion, which is a byproduct of the glycolytic metabolic process, is treated as a competitive inhibitor for Ca2+ ion. Since H+ is a competitive inhibitor (according to our assumption), its effect is equated to the strength of the Cai dissociation constant Kh. In the model, a Ca2+ binding site is assumed to exist in the inner membrane of the voltage-gated Ca2+ channel. The model predicts that a spike and burst electrical pattern can be generated by varying kca and that a given pattern may produce different levels of intracellular Ca2+ depending on Kh. In other words, it predicts that levels of [Ca2+]i can be separated from the electrical activity by controlling the concentration of glucose and pH appropriately. This may account for the experimental observation of Lebrun et al. (1985) that insulin secretion is not correlated to the burst of electrical activity.

Congenital murine polycystic kidney disease. I. The ontogeny of tubular cyst formation

In the current study, the ontogeny of tubular cyst formation was studied in the CPK mouse, a murine strain with autosomal recessive polycystic kidney disease. Utilizing the technique of intact nephron microdissection in addition to standard light and transmission electron microscopy, the earliest morphologic alterations in CPK kidneys were localized in fetal tissue at 17 days of gestation to the distal portion of developing proximal tubules. During disease progression, from birth to 21 days of postnatal age, there was a shift in the site of cystic nephron involvement from proximal tubule to collecting tubules without involvement of other nephron segments. Cysts were enlarged tubular segments which remained in continuity with other portions of the nephron and were not associated with abnormalities in the overall pattern of nephron growth or differentiation. Analysis suggested that alterations in transtubular transport in abnormally shortened proximal tubular segments of juxtamedullary nephrons may have pathogenic importance in the early stages of cyst formation, and that epithelial hyperplasia and cytoskeletal alterations may have a role in progressive proximal tubular cystic enlargement. Cellular hyperplasia of epithelial walls of normally formed tubules was a prominent feature of cyst formation and progressive enlargement in collecting tubules. Such data form the basis for future studies into specific pathophysiological processes which may be operative in specific nephron segments during different stages of cyst formation in the CPK mouse.

Microscopic features of canine renal dysplasia

Forty-five cases of renal dysplasia in dogs are examined. Microscopic lesions of dysplasia include asynchronous differentiation of nephrons, persistent mesenchyme, persistent metanephric ducts, atypical tubular epithelium, and dysontogenic metaplasia. These may be distinguished from secondary lesions including compensatory hypertrophy and hyperplasia of the nephron and a variety of degenerative and inflammatory lesions. Although morphological features of renal dysplasia in dogs differ somewhat from those in man, microscopic criteria used in the diagnosis of human dysplasia may be useful when applied to the dog.

Cardiac cellular electrophysiology: past and present

The time-course of the cardiac action potential can be accounted for in terms of ionic currents crossing the cell membranes. Depolarizing current is carried by Na+ or Ca2+ entering the cells, repolarizing current by K+ leaving the cells. Membrane permeability for the passive movement of these ions is thought to be voltage-dependent as well as time-dependent. Net transfer of charge may also result from active transport, 2 Na+ out against 1 K+ in; or coupled exchange, 3 or 4 Na+ in against 1 Ca2+ out. This review follows the path by which present-day knowledge has been reached. It also gives a few examples to illustrate that electrophysiology has provided concepts useful to clinical cardiology.

Comparative pathology of canine hereditary nephropathies: an interpretive review

Hereditary nephropathies in dogs represent multiple complex clinicopathological entities which cause renal failure in juvenile, adolescent, and young adult dogs. To date, nephropathies believed to have a genetic basis have been described in 11 breeds. These disorders represent a variety of developmental, degenerative, and metabolic defects. Many canine hereditary nephropathies are analogous to childhood nephropathies in man. Review of the veterinary literature, comparative pathology, and avenues of future research are discussed.

Transmembrane ion distribution and insulin secretion

The sodium dependence of insulin release was studied with the in vitro perfused principal islet of channel catfish. When extracellular sodium was replaced with choline, glucose-induced insulin release and glucose enhancement of arginine-induced insulin release were selectively abolished. Lowering the extracellular pH from 7.6 to 7.1 had a similar selective effect on glucose-induced insulin release. It is suggested that the Na:H antiport is responsible for the sodium dependence of insulin release and that a lowered cytosolic pH preferentially inhibits the glucose sensing mechanism.

Na+-H+ exchange in the process of glucose-induced insulin release from the pancreatic B-cell. Effects of amiloride on 86Rb, 45Ca fluxes and insulin release

The effect of amiloride, an inhibitor of Na+-H+ exchange, on intracellular pH (pHi), 86Rb outflow, 45Ca outflow and insulin release from pancreatic rat islets was examined. In the 0.1-1 mM range, amiloride transiently reduced pHi of glucose-deprived islets and allowed glucose to induce a sustained decrease in pHi of the islet cells. Amiloride reproduced the effect of glucose to decrease 86Rb and 45Ca outflow. In the presence of glucose (5.6 mM or more), amiloride (100 microM) acted synergistically with the sugar to reduce K+ outflow, and to stimulate 40Ca inflow and insulin release from perifused islets. These results add strong support to the view that the generation of protons through the metabolism of glucose represents an important step in the process of glucose-induced release. The stimulation by glucose of Na+-H+ exchange apparently masks and even overcomes the glucose-induced decrease in pHi otherwise expected from the increase in catabolic fluxes.

Differences in long-term effects of L-glutamine and D-glucose on insulin release from rat pancreatic islets

We have compared the effects of long-term exposure to L-glutamine or D-glucose on nutrient-induced insulin release from pancreatic islets of the rat. After 3 days of culture islets were finally tested in 1 h incubations for insulin responses to 16.7 mM of glucose, glutamine, leucine or a combination of leucine and glutamine. After culture at 11 mM glucose + 2 mM glutamine (A), glucose, leucine and glutamine stimulated release to a similar extent from islets. After culture at 1.7 mM glucose + 10 mM glutamine (B), only leucine stimulated insulin release. After culture at 11 mM glucose + 10 mM glutamine (C), both leucine and glutamine increased the insulin response. After culture at 1.7 mM glucose and 2 mM glutamine (D), only glutamine slightly stimulated release. After culture in high glutamine (B or C), a combination of leucine and glutamine significantly inhibited release as compared to leucine alone. A switch in culture media from B to A for 1 h prior to final incubations revived insulin release in response to glucose but not to glutamine. The reverse switch (A to B) abolished both subsequent glucose-and glutamine-induced insulin release. A switch from D to B revived an insulin response to leucine. Exposure of B-cells to 11 mM glucose during 30 min in another experimental system (perfused pancreas) induced a significant insulin response to subsequent stimulation with glutamine; this response was, however, only 17% of that to glucose per se observed in the same experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct evidence for opposite effects of D-glucose and D-glyceraldehyde on cytoplasmic pH of mouse pancreatic beta-cells

The effects of D-glucose, D-glyceraldehyde, glibenclamide, D-600, NH4+ and high concentrations of K+ on cytoplasmic pH (pHi) were investigated in dispersed and cultured pancreatic beta-cells from ob/ob mice. The cytoplasmic pH was measured with the fluorescent H+-indicator quene 1. The average pHi value in resting beta-cells was 6.71. Addition of 20 mM of the physiological stimulus D-glucose increased pHi with 0.05 units. Both glibenclamide and high concentrations of K+ decreased pHi. The latter effects were completely reversed by D-600, supporting the notion that free cytoplasmic Ca2+ can be involved in the regulation of pHi. In contrast to D-glucose, 10 mM of D-glyceraldehyde decreased pHi by 0.09 units, an effect persisting even in the presence of D-600. From the present study it is evident that D-glyceraldehyde and D-glucose have opposite effects on pHi in pancreatic beta-cells.