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G A Langer

Publications and source records attributed to G A Langer.

At least 55 records · Page 3Linked to original sources
PubMed1991

Myocardial calcium compartmentation and contractile control.

Under the condition of rapid perfusion, the time course of contractile response of single ventricular cells to extracellular calcium (Ca) depletion and repletion identifies "fast" and "slow" cellular Ca pools. 45Ca exchange was studied in these cells under the same conditions of on-line rapid perfusion. Four kinetically-defined compartments were distinguished: (1) A "rapid" compartment containing 2.6 mmoles Ca/kg dry wt of lanthanum (La) displaceable Ca, t1/2 less than 1 sec.; (2) An "intermediate" compartment(s) containing 2.1 mmoles, t1/2 = 3 and 19 sec. Caffeine displaced significant amounts of Ca from this compartment whereas La displaced none; (3) A "slow" compartment containing 1.6 mmoles, t1/2 = 3.6 min. Addition of inorganic phosphate to the perfusate adds significant amounts of Ca to this compartment; (4) An "inexchangeable" compartment, containing 1.2 mmoles. The "rapid" compartment's flux is greater than or equal to 300 mumoles Ca/kg wet wt/sec. Its exchange rate indicates that it is the kinetic counterpart of the functionally-defined "fast" pool. Its subcellular locus is undefined. The "intermediate" compartment is best correlated with the "slow" pool and represents Ca in the sarcoplasmic reticulum. The "slow" compartment contains a significant fraction from the mitochondria. The results indicate that greater than or equal to 40% of cellular Ca can turn over within the period of one contraction cycle. These results are consistent with the following sequence: (1) Upon sarcolemmal depolarization, Ca moves through the Ca channel to arrive at the SR and at the myofilaments. (2) Ca induced Ca release occurs via the "feet" at the SR-inner SL region.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Calcium compartmentation and exchange rates in primary hepatocyte culture.

We utilized a technique, previously used to study myocardial cells (G. A. Langer, J. S. Frank, and L. M. Nudd, 1979, Amer. J. Physiol. 237, H239-H246), to study 45Ca2+ isotope exchange kinetics in hepatocyte monolayers, cultured on scintillation disks, and perfused in a flow-through chamber. Isolated rat hepatocytes were plated directly on Primaria-coated disks impregnated with scintillation fluors which made up the walls of the perfusion chamber. Following the labeling of the cells with radioactive calcium (45Ca2+), to apparent asymptote, the washout of 45Ca2+ from the cells was measured. A large very fast turnover compartment, as well as small fast and slow turnover compartments, were identified in each experiment. Surface calcium (Ca2+) was determined by its displacement with 1 mM La3+ after asymptote had been reached during 45Ca2+ labeling (1.59 mmol Ca2+/kg dry wt). The rate constant for this compartment was faster than the washout of the chamber (greater than 3.4 min-1 with a t1/2 less than 12 s). The rate constants for the fast and slow exchangeable compartments were 0.11 min-1 (t1/2 = 6.5 min) and 0.013 min-1 (t1/2 = 56 min), respectively. The fast compartment contained 0.40 mmol Ca2+/kg dry wt and the slow compartment contained 0.27 mmol Ca2+/kg dry wt. Neither the fast nor the slow compartment was lanthanum displaceable. Release of 45Ca2+ in response to 100 microM phenylephrine, 10 nM angiotensin II, and 100-microM 2,5-ditert-butyl hydroquinone was measured during the washout phase. Ca2+ released by these compounds was determined to be 0.50 mmol 0.44, and 0.43 mmol Ca2+/kg dry cell wt, respectively. These agents had an effect only during the washout of the fast compartment. In conclusion, this novel technique of on-line measurement of 45Ca2+ exchange in hepatocyte monolayers identified three exchangeable compartments: (1) a very rapidly exchangeable surface compartment, (2) a fast "microsomal" hormone-releasable compartment, and (3) a slow, non-hormone-releasable compartment.

Angiotensin II↗
PubMed1990

Heat production in isolated heart myocytes: differences among species.

A new calorimetry method has been developed to measure heat production from heart cell suspensions under continuous perfusion. The method is technically independent of the temperature at which the measurements are made, allows full control of the perfusion media, and is suitable for various biological preparations such as cells from diverse tissues, membrane vesicles, or skinned cells. The resting heat rate (Hr) measured at 18.5 degrees C in three different species (19.2 +/- 0.43, 12.8 +/- 0.56, and 9.4 +/- 0.52 mW/g dry wt for rat, guinea pig, and rabbit ventricular myocytes, respectively) agrees with that obtained with other methodologies such as oxygen consumption, thermopiles, and whole heart calorimetry. The Hr measurements showed an excellent correlation with the percentage of rod-shaped cells, indicating that rounded cells are metabolically inactive. Although the time course of the effect of increasing extracellular [K] was dependent on the species, the new steady level of Hr observed under higher extracellular [K] was significantly higher in all three species (+8.3 +/- 1.2, +9.5 +/- 4.0, and +9.3 +/- 2.7 mW/g dry wt for rat, guinea pig, and rabbit ventricular cells, respectively). This indicates that the commonly used "arrested-heart" preparation (with high extracellular [K]) for evaluation of basal metabolism most probably overestimates the real resting values. The present results also show that the wide range of resting metabolism reported in whole tissue is not due to cellular heterogeneity nor to myocyte interaction and supports the idea of an inverse relationship between resting metabolism and body weight or animal size across species.

Animals↗
PubMed1990

Ca exchange under non-perfusion-limited conditions in rat ventricular cells: identification of subcellular compartments.

Freshly prepared ventricular myocytes from rat hearts, aliquots of which were tested for sarcolemmal integrity by La exposure, were labeled at high 45Ca specific activity. Isotope was subsequently washed out at a perfusion rate of 2.8 ml/s with washout solution sampled each 1 s. No initial unrecorded period of washout was imposed. Four compartments were distinguishable: 1) a "rapid" compartment (RC) containing 2.6 mmol Ca/kg dry wt of La-displaceable Ca, half time (t1/2) less than 1 s; 2) an "intermediate" compartment(s) (IC) containing 2.1 mmol, t1/2 = 3 and 19 s; 3) a "slow" compartment (SC) containing 1.6 mmol, t1/2 = 3.6 min; 4) an "inexchangeable" compartment that demonstrated no 45Ca uptake after 60-min labeling containing 1.2 mmol. Introduction of 10 mM caffeine as a probe for sarcoplasmic reticulum (SR) content at various times during the washouts caused an increased release of 45Ca. The net increased 45Ca release plotted as a function of time at which caffeine was introduced produced a biexponential curve with t1/2s of 2 and 22 s, very similar to the t1/2s of the IC. Ryanodine (1 microM) significantly reduced the caffeine-induced 45Ca release, confirming the SR locus of the IC. Cells were perfused with 10 mM NaH2PO4 to specifically increase mitochondrial 45Ca labeling. Subsequent removal of PO4 at various times during washouts produced large increases in effluent 45Ca. A plot of the net peak release of 45Ca vs. time of PO4 removal was monoexponential with t1/2 = 3.3 min, very similar to the SC t1/2. The large La-accessible RC remains unlocalized, but the rapidity of its exchange places it in the sarcolemma and/or at sites in rapid equilibrium with the sarcolemma.

Animals↗
PubMed1990

Contraction and sarcoplasmic reticulum Ca2+ content in single myocytes of guinea pig heart: effect of ryanodine.

The relationship between the ability of sarcoplasmic reticulum (SR) to accumulate and retain Ca2+ and the electrically stimulated contractions (ESCs) of isolated cells from guinea pig ventricular myocardium was investigated. Caffeine contractures or rapid cooling contractures were used as a relative measure of the SR Ca2+ content. Depletion of SR Ca2+ by short exposure to caffeine (15 mM) or by prolonged rest resulted in a reduction of the amplitude of the ESCs by 83 +/- 14 and 65 +/- 11% (means +/- SD), respectively. This result points to SR as a major source of the Ca2+ that activates contraction. However, depriving the SR of the ability to retain Ca2+ by means of prolonged (up to 75 min) exposure to 0.1 microM ryanodine (as shown by the absence of contractile response to caffeine or cooling) did not prevent an ESC of nearly normal amplitude (81 +/- 24% control), albeit with a reduced contraction velocity and a time to peak contraction prolonged by 51 +/- 11%. Additionally, while rest decay of ESCs was present after ryanodine treatment, the time for the ESCs to recover their steady-state amplitude was prolonged at least twofold. Thus, in contrast with the normal guinea pig cells, ESCs of the myocytes exposed to ryanodine are controlled by sarcolemmal processes. This change in the state of excitation-contraction coupling results mainly in modification of the time course of the ESCs and of the time course of the response of the cells to the change in the rate of stimulation.

Animals↗
PubMed1989

Animal research and government policy.

In the report "Synthetic CD4 peptide derivatives that inhibit HIV infection and cytopathicity" by Jeffrey D. Lifson et al. (5 Aug., p. 712), the last seven residues of the CD4 peptide (26-50) should have been SFLTKGP rather than STLTKGP.

Animals↗
PubMed1989

Rapid, non-perfusion-limited calcium exchange in cultured neonatal myocardial cells.

Neonatal rat myocardial cells culture are used to study the effects of zero [Ca]0 and lanthanum (La3+) on contractile function and to correlate these findings with steady-state 45Ca exchange. A rapid superfusion system is used to study cell shortening. At a stimulation rate of 1 Hz exposure to Ca2+ free solution for 900 ms abolishes contraction. Contraction is fully restored within 900 ms after return to 1 mM Ca2+ solution. Similarly, contraction is abolished 800 ms after changing to a 1 mM La3+ solution, but does not return for several min after removal of La3+. A modification of the scintillation-disc flow cell technique is used to study steady-state 45Ca exchange. Cells are grown directly on scintillant plastic discs pre-treated by the Primaria process which enhances cell adhesiveness. The cells on the discs are inserted into a specially designed flow cell which is then perfused at a rate of 500 ml/min. In this manner the labeling period, intervention and washout are performed while instantaneously and continuously monitoring the 45Ca activity without the need to interpose an unmonitored wash period. In addition, the use of on-line computer monitoring allows an accurate and precise recording of data as often as 6 times/s. This permits the identification of the following four Ca2+ compartments: (1) A rapidly exchanging compartment which is La3+ displaceable, contains 2.59 mmols Ca2+/kg dry cells and has a t1/2 = 1.5 s; (2) An intermediate component composed of two compartments which contain 0.43 and 0.22 mmols Ca2+/kg dry cells and exchange with t1/2 of 19 and 103 s respectively; (3) A slowly exchangeable compartment which contains 0.69 mmols Ca2+/kg dry cells with t1/2 = 19 min; (4) An unexchangeable compartment which contains 6.24 mmols Ca2+/kg dry cells. The rapid compartment is La3+ displaceable and has a flux of greater than 1100 mumols Ca2+/kg dry cells/s. This is the first time that the kinetics and sizes of the rapid Ca2+ compartment and intermediate compartments have been measured. Correlation of contractile response to zero [Ca]0 and La3+ administration with 45Ca exchange measurements under conditions of ultra-rapid perfusion indicate that at least a portion of the La3+-displaceable rapid component is critical in the beat-to-beat control of contractile force.

Animals↗
PubMed1989

Calcium is rapidly exchangeable in cultured vascular smooth muscle cells from rabbit aorta.

Calcium exchange was measured in enzymatically isolated, cultured smooth muscle cells from the rabbit thoracic aorta. Cells were grown to confluence in monolayer on scintillator discs which were then inserted into a modified flow cell/spectrometer to measure 45Ca exchange in a continuous, on-line manner. This also allowed us to measure rapid movements of cellular Ca2+ without solubilizing the cells. Two components of Ca2+ exchange were detected: a La3+-displaceable, rapidly exchangeable fraction (t 1/2 = 15.6 s) and a slowly exchangeable fraction (t 1/2 = 34.5 min). The La3+ displaceable, rapidly exchangeable Ca2+ fraction represented 57 to 61% of the total exchangeable Ca2+. Multiple passaging of cells did not after the Ca2+ flux characteristics. Low Na+ perfusion increased smooth muscle cell Ca2+ flux by 6.71 mmol/kg dry weight. This increase was localized to both the rapidly and slowly exchangeable Ca2+ compartments. Ouabain, an inhibitor of the plasmalemmal Na+ -K+ pump, also increased net uptake of 45Ca. The results demonstrate that approximately 60% of exchangeable Ca2+ of smooth muscle cells is very rapidly exchangeable (t 1/2 less than 16 s). The results stress the importance of measuring 45Ca2+ movements in an on-line, continuous manner in order to ensure detection of the majority of total exchangeable Ca2+ in smooth muscle cells.

Animals↗
PubMed1989

Neuraminidase selectively enhances transient Ca2+ current in cardiac myocytes.

Sialic acid, an anionic sugar moiety found peripherally on membrane glycoconjugates, is specifically hydrolyzed from the cell surface by neuraminidase. Because neuraminidase has previously been demonstrated to augment myocardial cell calcium content, the effects of neuraminidase on Ca channel function were studied on voltage-clamped guinea pig ventricular myocytes. In 25-50% of cells, neuraminidase treatment (0.12 U/ml for 20 min) enhanced current through the transient (T) Ca channel by 304 +/- 35% without significantly altering the magnitude of the long-lasting (L) Ca channel current. Exposure to neuraminidase did not affect the voltage dependence of activation or inactivation, nor did it affect the selective inhibition of the T-channel current by amiloride or the L-channel current by nifedipine. After neuraminidase treatment, the T-channel current inactivated more rapidly (time constant decreasing from 8.9 +/- 0.9 to 7.7 +/- 0.6 ms), whereas there was no change in the rate of inactivation of the L-channel current. Neuraminidase treatment removed approximately 20% of the total cellular sialic acid. These results indicate that neuraminidase treatment selectively modulates the function of the T Ca channel in ventricular myocytes, possibly through removal of sarcolemmal sialic acid, suggesting that glycosylation of membrane macromolecules may influence membrane function.

Animals↗
PubMed1989

Contractile shortening response of ventricular cells to extracellular acidosis. Evidence for two-site control of H+-Ca2+ interaction.

The effect of extracellular acidosis on contraction of single isolated ventricular cells from rabbit was measured in a system in which pHo could be changed in less than 200 msec. The contractile response to acidotic levels was complete within 25 seconds. The response was measured 30 seconds after pHo was decreased to 7.0, 6.5, 6.0, and 5.5 at each of 8 [Ca]o levels (0.125-4.0 mM). Cell shortening versus [Ca]o was plotted to construct a curve for each pHo level, with each point relative to shortening at pH 7.5, [Ca]o = 1 mM (100% value). Calcium current (1 mM [Ca]o) was also measured 30 seconds after pHo was decreased from 7.5 to 6.5 with single-cell patch clamp technique. The contractile response to extracellular acidosis is accurately predicted by assuming two (probably sarcolemmal) sites at which H+ ions affect calcium binding and/or flux: (equation; see text) The first factor represents a set of sites that are proposed to control access, dependent on the degree of their ionization, to sites represented by the second factor. The latter sites are proposed to accept calcium according to mass-action law. The response of calcium channel current to extracellular acidosis was also complete and reversible within 25 seconds. The current response indicates that the two-site model could be predictive for the effect of extracellular acidosis on calcium current in ventricular cells.

Acidosis↗
PubMed1988

Phospholipid asymmetry in cardiac sarcolemma. Analysis of intact cells and 'gas-dissected' membranes.

The investigation focuses on the phospholipid composition of the sarcolemma of cultured neonatal rat heart cells and on the distribution of the phospholipid classes between the two monolayers of the sarcolemma. The plasma membranes are isolated by 'gas-dissection' technique and 38% of total cellular phospholipid is present in the sarcolemma with the composition: phosphatidylethanolamine (PE) 24.9%, phosphatidylcholine (PC) 52.0%, phosphatidylserine/phosphatidylinositol (PS/PI) 7.2%, sphingomyelin 13.5%. The cholesterol/phospholipid ratio of the sarcolemma is 0.5. The distribution of the phospholipids between inner and outer monolayer is defined with the use of two phospholipases A2, sphingomyelinase C or trinitrobenzene sulfonic acid as lipid membrane probes in whole cells. The probes have access to the entire sarcolemmal surface and do not produce detectable cell lysis. The phospholipid classes are asymmetrically distributed: (1) the negatively charged phospholipids, PS/PI are located exclusively in the inner or cytoplasmic leaflet; (2) 75% of PE is in the inner leaflet; (3) 93% of sphingomyelin is in the outer leaflet; (4) 43% of PC is in the outer leaflet. The predominance of PS/PI and PE at the cytoplasmic sarcolemmal surface is discussed with respect to phospholipid-ionic binding relations between phospholipids and exchange and transport of ions, and the response of the cardiac cell on ischemia-reperfusion.

Animals↗
PubMed1988

Two components of coupling calcium in single ventricular cell of rabbits and rats.

A system for rapid superfusion with simultaneous measurement of contractile amplitude of single adult rat and rabbit ventricular cells is used to measure cellular response to alterations of the superfusate achieved in less than 0.3 s. The time course of contractile response of the cells to extracellular Ca concentration [( Ca]o) depletion and repletion identifies "fast" and "slow" cellular pools of Ca that contribute to contraction. The fast pool can be totally depleted or repleted within a single diastolic period. Depletion of this pool completely eliminates contraction in both rat and rabbit cell. Experiments using dimethonium to investigate the effect of Ca in the diffuse double layer and dodecyl sulfate to specifically augment sarcolemmal fixed-negative charge indicate that sarcolemmal binding sites may represent a major fraction of the fast pool. At 1 mM [Ca]o, this pool is functionally saturated in the rat but not nearly saturated in the rabbit. After 10 min Ca depletion more than 60 s of Ca repletion are required to restore full contraction amplitude. This indicates the presence of a slow pool of Ca that contributes to contraction. This pool, at 1 mM [Ca]o, is nearly functionally saturated in the rabbit but not nearly so in the rat. The responses to Ca depletion and repletion, Na depletion and repletion, and 1 microM ryanodine indicate that the contribution of Ca to contraction from the slow pool is much greater in the rat than in the rabbit and that its cellular locus is probably the sarcoplasmic reticulum.

Animals↗
PubMed1987

The role of calcium at the sarcolemma in the control of myocardial contractility.

The importance of sarcolemmal-bound calcium (Ca) in the control of contraction in mammalian myocardium is indicated by the following results. The curve that relates [Ca]o (from 50 microM to 10 mM) to force development and that which relates [Ca]o to Ca bound to a highly purified sarcolemmal fraction are superimposable. The ability of a series of cations to uncouple excitation from contraction is the same as their relative ability to displace Ca from the sarcolemma. Dimethonium, which specifically displaces cation from the diffuse double layer of the cellular surface, has little effect on contractile force. This indicates that the Ca actually bound to the sarcolemma is the surface Ca important in contractile control. Polymyxin B, a highly charged cationic amphiphilic peptidolipid, specifically competes for Ca-binding sites on anionic and zwitterionic phospholipid. It is a potent displacer of Ca from myocardial cells and purified sarcolemma and a potent uncoupler. Phospholipase D cleaves the nitrogenous base from sarcolemmal phospholipid with production of anionic phosphatidic acid. Phospholipase D treatment increases Ca bound to cells and purified sarcolemma and increases force development of ventricular tissue from both neonatal rat and adult rabbit. Insertion of charged amphiphiles in the sarcolemma as phospholipid analogues modulate interaction of Ca with the sarcolemma, e.g., anionic dodecylsulfate increases Ca bound to sarcolemmal vesicles by more than 80% and increases force development in rabbit papillary muscle by 100%. The effect of pH variation on Ca binding to phospholipid extracted from sarcolemma indicates that phospholipid accounts for at least 75% of the binding. The current model proposes a two-site control of Ca binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Calcium exchange, structure, and function in cultured adult myocardial cells.

Cells digested from adult rat heart and cultured for 14 days demonstrate all the structural elements, in mature form, associated with the process of excitation-contraction (EC) coupling. The transverase tubular (TT) system is well developed with an extensive junctional sarcoplasmic reticulum (JSR). In nonphosphate-containing buffer contraction of the cells is lost as rapidly as zero extracellular Ca concentration ([Ca]o) solution is applied (less than 10 s) and a negative contraction staircase is produced on increase of stimulation frequency. Structurally and functionally the cells have the characteristics of adult cells in situ. 45Ca exchange and total 45Ca measurement in N-2-hydroxyethylpiperazine N'-2-ethanesulfonic acid (HEPES)-buffered perfusate define three components of cellular Ca: a rapidly exchangeable component (t1/2 less than 25 s) accounting for 36% of total Ca, a slowly exchangeable component (t1/2 53 min) accounting for 7% of total Ca, and the remaining 57% cellular Ca is "inexchangeable" (demonstrates no significant exchange within 60 min). The slowly exchangeable component can be increased 10-fold within 60 min by addition of phosphate to the perfusate. The Ca distribution and exchange characteristics are little different from those of 3-day cultures of neonatal rat heart previously studied [Langer, G. A., J. S. Frank, and L. M. Nudd. Am. J. Physiol. 237 (Heart Circ. Physiol. 6): H239-H246, 1979]. The results suggest that the cells are representative of adult cells in situ and that both sarcolemmal-bound and sarcoplasmic reticular Ca contribute to the component of Ca that is rapidly exchangeable.

Animals↗
PubMed1987

Trans-sarcolemmal Ca2+ movements associated with contraction of the rabbit right ventricular wall.

The purpose of this study was to examine the movements of Ca2+ into the myocardium from the extracellular space during the course of muscle contraction. Equilibration of the rabbit right ventricular wall with perfusate containing 45Ca was measured by collecting effluent droplets over time. This protocol was carried out in a quiescent muscle and then repeated 15-20 minutes later in an identical fashion except that halfway through the collection period the muscle was stimulated to contract. We were thus able to quantitate the contraction-dependent changes in 45Ca movements. In control experiments using [58Co]EDTA as an extracellular space marker, we observed that contraction altered the volume of this space. This alteration in extracellular space was relatively small, and the quantitation of 45Ca movements was corrected for this change. The addition of 1 microM Bay K 8644 to the perfusate stimulated tension and augmented Ca2+ depletion from the extracellular space. The addition of 15 microM nifedipine to the perfusate significantly reduced both tension development and Ca2+ depletion from the extracellular space of the muscle. Net contraction-dependent movement of Ca2+ from the extracellular space into the myocardium under control conditions at 1 mM [Ca2+] was 10-14 mumol Ca2+/kg tissue wet wt/beat. This value indicates either a large contribution of Ca2+-induced Ca2+ release from the sarcoplasmic reticulum and/or significant contribution of sarcolemmal bound Ca2+ to excitation-contraction coupling in the rabbit ventricle.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Cardiac ischemia. Part II--Reperfusion and treatment.

An edited summary of an Interdepartmental Conference arranged by the Department of Medicine of the UCLA School of Medicine, Los Angeles. The Director of Conferences is William M. Pardridge, MD, Professor of Medicine.

Angioplasty, Balloon↗