Biomedical subjects

N S Dhalla

Publications and source records attributed to N S Dhalla.

At least 181 records · Page 10Linked to original sources

PubMed1987

Inhibition of Na+-Ca2+ exchange in heart sarcolemmal vesicles by phosphatidylethanolamine N-methylation.

The effect of phosphatidylethanolamine N-methylation on Na+-Ca2+ exchange was studied in sarcolemmal vesicles isolated from rat heart. Phosphatidylethanolamine N-methylation following incubation of membranes with S-adenosyl-L-methionine, a methyl donor for the enzymatic N-methylation, inhibited Nai+-dependent Ca2+ uptake by about 50%. The N-methylation reaction did not alter the passive permeability of the sarcolemmal vesicles to Na+ and Ca2+ and did not modify the electrogenic characteristics of the exchanger. The depressant effect of phosphatidylethanolamine N-methylation on Nai+-dependent Ca2+ uptake was prevented by S-adenosyl-L-homocysteine, an inhibitor of the N-methylation. Pretreatment of sarcolemma with methyl acetimidate hydrochloride, an amino-group-blocking agent, also prevented methylation-induced inhibition of Ca2+ uptake. In the presence of exogenous phospholipid substrate, the phospholipid N-methylation process in methyl-acetimidate-treated sarcolemmal vesicles was restored and the inhibitory effect on Ca2+ uptake was evident. These results suggest that phosphatidylethanolamine N-methylation influences the heart sarcolemmal Na+-Ca2+ exchange system.

Animals↗

PubMed1987

Sarcolemmal phospholipid N-methylation in genetically determined hamster cardiomyopathy.

The heart sarcolemmal phosphatidylethanolamine N-methylation in UM-X7.1 strain of cardiomyopathic hamsters was examined by using 0.055, 10 and 150 microM S-adenosyl-L-(methyl-3H) methionine as methyl donor for sites I, II and III, respectively. In comparison with control values, methylation activities at site I was increased in 40, 120 and 250 days old cardiomyopathic hamsters. On the other hand, methylation activities at sites II and III in 120 and 250 days old cardiomyopathic animals were depressed without any change in the 40 days old group. The alterations in N-methylation activities were associated with kinetic changes in apparent Vmax values without any changes in the apparent Km. These results indicate a defect in the phospholipid N-methylation process in heart sarcolemma during the development of genetically determined cardiomyopathy.

Aging↗

PubMed1987

Activation of Ca2+/Mg2+ ATPase in heart sarcolemma upon electrical stimulation.

Electrical stimulation of the rat heart sarcolemmal membranes with a square wave current was found to increase Ca2+-ATPase activity. This activation of the enzyme was dependent upon the voltage of the electric current, frequency of stimulation and duration of stimulation of the sarcolemmal membranes. The increase in Ca2+-ATPase was reversible upon terminating the electrical stimulation. The activation of sarcolemmal Ca2+-ATPase due to electrical stimulation was markedly depressed when the reaction was carried out at high pH (7.8 to 8.2), low pH (6.6 to 7.0), high temperatures (45 to 50 degrees C) and low temperatures (17 to 25 degrees C) of the incubation medium. Ca2+-antagonists, verapamil and D-600, unlike other types of inhibitors such as propranolol and ouabain, were found to reduce the activation of sarcolemmal Ca2+-ATPase by electrical stimulation. These results support the view that Ca2+/Mg2+ ATPase may be involved in the gating mechanism for opening Ca2+-channels in the sarcolemmal membrane upon excitation of the cardiac muscle.

Animals↗

PubMed1987

A comparative study of the rat heart sarcolemmal Ca2+-dependent ATPase and myosin ATPase.

In order to gain some information regarding Ca2+-dependent ATPase, the enzyme was purified from cardiac sarcolemma and its properties were compared with Ca2+-ATPase activity of myosin purified from rat heart. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by Ca2+ but the maximal activation of Ca2+-dependent ATPase required 4 mM Ca2+ whereas that of myosin ATPase required 10 mM Ca2+. These ATPases were also activated by other divalent cations in the order of Ca2+ greater than Mn2+ greater than Sr2+ greater than Br2+ greater than Mg2+; however, there was a marked difference in the pattern of their activation by these cations. Unlike the myosin ATPase, the ATP hydrolysis by Ca2+-dependent ATPase was not activated by actin. The pH optima of Ca2+-dependent ATPase and myosin ATPase were 9.5 and 6.5 respectively. Na+ markedly inhibited Ca2+-dependent ATPase but had no effect on the myosin ATPase activity. N-ethylmaleimide inhibited Ca2+-dependent ATPase more than myosin ATPase whereas the inhibitory effect of vanadate was more on myosin ATPase than Ca2+-dependent ATPase. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by K-EDTA and NH4-EDTA. When myofibrils were treated with trypsin and passed through columns similar to those used for purifying Ca2+-ATPase from sarcolemma, an enzyme with ATPase activity was obtained. This myofibrillar ATPase was maximally activated at 3-4 mM Ca2+ and 3 to 4 mM ATP like sarcolemmal Ca2+-dependent ATPase. K+ stimulated both ATPase activities in the absence of Ca2+ and inhibited in the presence of Ca2+. Both enzymes were inhibited by Na+, Mg2+, La3+, and azide similarly. However, Ca2+ ATPase from myofibrils showed three peptide bands in SDS polyacrylamide gel electrophoresis whereas Ca2+ ATPase from sarcolemma contained only two bands. Sarcolemmal Ca2+-ATPase had two affinity sites for ATP (0.012 mM and 0.23 mM) while myofibrillar Ca2+-ATPase had only one affinity site (0.34 mM). Myofibrillar Ca2+-ATPase was more sensitive to maleic anhydride and iodoacetamide than sarcolemmal Ca2+-ATPase. These observations suggest that Ca2+-dependent ATPase may be a myosin like protein in the heart sarcolemma and is unlikely to be a tryptic fragment of myosin present in the myofibrils.

Adenosine Triphosphatases↗

PubMed1987

Decreased Ca2+-binding and Ca2+-ATPase activities in heart sarcolemma upon phospholipid methylation.

Heart sarcolemma has been shown to possess three catalytic sites (I, II and III) for methyl transferase activity (Panagia V, Ganguly PK and Dhalla NS. Biochim Biophys Acta 792:245-253, 1984). In this study we examined the effect of phosphatidylethanolamine N-methylation on ATP-independent Ca2+ binding and ATPase activities in isolated rat heart sarcolemma. Both low affinity (1.25 mM Ca2+) and high affinity (50 microM Ca2+) Ca2+ binding activities were decreased following incubation of sarcolemmal membranes with AdoMet under optimal conditions for site II and III. Similarly, Ca2+ ATPase activities measured at 1.25 mM and 4 mM Ca2+ were depressed by phospholipid N-methylation. S-adenosyl homocysteine, a specific inhibitor of phospholipid N-methylation, prevented the depression of low affinity Ca2+ binding and Ca2+ ATPase activities, whereas the methylation-induced effect on the high affinity Ca2+ binding was not influenced by this agent. Pretreatment of sarcolemma with methyl acetimidate hydrochloride, an amino group blocking agent, also prevented the methylation-induced inhibition of both Ca2+ binding and Ca2+ ATPase. A further decrease in Ca2+ binding and Ca2+ ATPase activities together with a marked increase in the intramembranal level of PC was seen when membranes were methylated under the site III conditions in the presence of phosphatidyldimethylethanolamine as exogenous substrate. There was no effect of phospholipid methylation on sarcolemmal Na+-K+ ATPase and Mg2+ ATPase activities. These results indicate a role of phospholipid N-methylation in the regulation of sarcolemmal Ca2+ ATPase and low affinity ATP-independent Ca2+ binding.

Animals↗

PubMed1987

Solubilization of a divalent cation dependent ATPase from dog heart sarcolemma.

Heart sarcolemma has been shown to contain an ATPase hydrolyzing system which is activated by millimolar concentrations of divalent cations such as Ca2+ or Mg2+. Although Ca2+-dependent ATPase is released upon treating sarcolemma with trypsin, a considerable amount of the divalent cation dependent ATPase activity was retained in the membrane. This divalent cation dependent ATPase was solubilized by sonication of the trypsin-treated dog heart sarcolemma with 1% Triton X-100. The solubilized enzyme was subjected to column chromatography on a Sepharose-6B column, followed by ion-exchange chromatography on a DEAE cellulose column. The enzyme preparation was found to be rather labile and thus the purity of the sample could not be accurately assessed. The solubilized ATPase preparations did not show any cross-reactivity with dog heart myosin antiserum or with Na+ + K+ ATPase antiserum. The enzyme was found to be insensitive to inhibitors such as ouabain, verapamil, oligomycin and vanadate. The enzyme preparation did not exhibit any Ca2+-stimulated Mg2+ dependent ATPase activity. Furthermore, the low affinity of the enzyme for Ca2+ (Ka = 0.3 mM) rules out the possibility of its involvement in the Ca2+ pump mechanism located in the plasma membrane of the cardiac cell.

Adenosine Triphosphatases↗

PubMed1987

Alterations in Ca2+/Mg2+ ATPase activity upon treatment of heart sarcolemma with phospholipases.

In order to examine the role of phospholipids in the activation of membrane bound Ca2+/Mg2+ ATPase, the activities of Ca2+ ATPase and Mg2+ ATPase were studied in heart sarcolemma after treatments with phospholipases A, C and D. The Mg2+ ATPase activity was decreased upon treating the sarcolemmal membranes with phospholipases, A, C and D; phospholipase A produced the most dramatic effect. The reduction in Mg2+ ATPase activity by each phospholipase treatment was associated with a decrease in the Vmax value without any changes in the Ka value. The depression of Mg2+ ATPase in the phospholipase treated preparations was not found to be due to release of fatty acids in the medium and was not restored upon reconstitution of these membranes by the addition of synthetic phospholipids such as lecithin, lysolecithin or phosphatidic acid. In contrast to the Mg2+ ATPase, the sarcolemmal Ca2+ ATPase was affected only slightly by phospholipase treatments. The greater sensitivity of Mg2+ ATPase to phospholipase treatments was also apparent when deoxycholate-treated preparations were employed. These results indicate that glycerophospholipids are required for the sarcolemmal Mg2+ ATPase activity to a greater extent in comparison to that for the Ca2+ ATPase activity and the phospholipids associated with Mg2+ ATPase are predominantly exposed at the outer surface of the membrane.

Animals↗

PubMed1987

Biphasic changes in the sarcolemmal phosphatidylethanolamine N-methylation activity in catecholamine-induced cardiomyopathy.

Phosphatidylethanolamine (PE) N-methylation activity was studied in rat heart sarcolemma at 1, 3, 9 and 24 h after an intraperitoneal injection of isoproterenol (40 mg/kg). Three reaction sites for PE N-methylation were examined by assaying the incorporation of radiolabeled methyl groups from S-adenosyl-L-methionine (AdoMet) into sarcolemmal PE molecules under optimal conditions. Total methylation activity at catalytic site I (studied by employing 0.055 microM AdoMet) was increased at 1 and 3 h after the isoproterenol injection and depressed at 24 h; 9 h samples showed no change. Similar biphasic alterations were seen for phosphatidyl-N-monomethylethanolamine, the major methylated product formed at site I. Alterations in the methylation activity at site I were associated with changes in Vmax values but the apparent affinity for AdoMet remained unaltered. No alterations were found in total methylation activities at sites II and III in isoproterenol treated preparations when studied by employing 10 and 150 microM AdoMet, respectively. An increase and a decrease in the PE N-methylation activity at site I were also observed in the sarcoplasmic reticular (microsomal) fraction from experimental hearts after 1 h and 24 h of the isoproterenol injection respectively, without changes at sites II and III. On the other hand, no changes were seen in the mitochondrial fraction. These results indicate biphasic alterations in the sarcolemmal and microsomal PE N-methylation activities during the development of catecholamine-induced cardiomyopathy.

Animals↗

PubMed1987

Characterization of insulin receptors in cardiac sarcolemmal and sarcoplasmic reticular membranes.

Specific insulin binding sites in cardiac sarcolemmal (SL) and sarcoplasmic reticular (SR) membranes were examined. Under in vitro conditions, the specific insulin binding to SL was two to three times greater than that to SR isolated from myocardium of different species. Insulin binding to these membranes was rapid, saturable, and temperature dependent. Scatchard plots were nonlinear and revealed high-affinity sites with K1 of 1.2 +/- 0.1 and 2.3 +/- 0.4 nM and low-affinity sites with K2 of 34.0 +/- 11.6 and 87.7 +/- 18.7 nM for SR and SL membranes, respectively. Unlabeled insulin accelerated the dissociation of previously bound labeled insulin, reflecting negative cooperativity of site-to-site interaction in both membranes; however, the dissociation rate in SR was about twofold higher than that in SL. The optimum binding of insulin to SR showed a plateau between pH 6.5 and 7.5 in comparison with a sharp peak at pH 8.0 for SL. Insulin significantly enhanced ATP-dependent Ca2+ binding to SL and SR membranes by approximately 100 and 40%, respectively. The Na+-dependent Ca2+ uptake in SL and the oxalate-supported Ca2+ uptake in SR were also stimulated by insulin; the maximum increase in Ca2+ accumulation in these vesicles was approximately 150 and 25%, respectively. These studies indicate that specific insulin binding sites in SL are characteristically distinct from those in SR and that insulin is capable of stimulating Ca2+ pumps located in these membranes.

Animals↗

PubMed1987

Alterations in cardiac lysosomal hydrolases following induction of the calcium paradox.

Although perfusion of the heart with calcium-free medium for a brief period followed by reperfusion with calcium-containing medium results in marked structural derangements (calcium paradox), the mechanisms for this cell damage are far from clear. Since activation of lysosomal enzymes has been associated with pathological damage, it was the purpose of this study to examine alterations in the activities of several lysosomal enzymes in rat hearts subjected to calcium paradox. No significant changes in the activities of beta-acetylglucosaminidase, beta-galactosidase, alpha-mannosidase, or acid phosphatase were seen in the homogenates of hearts exposed to the calcium paradox. However, there were dramatic alterations in the lysosomal enzyme activities in the sedimentable and nonsedimentable fractions during calcium paradox. The lysosomal enzyme activities were also detected in the perfusate collected during reperfusion with calcium-containing medium. These changes occurred during the reperfusion period since no alterations were apparent after calcium-free perfusion and were dependent upon the time of reperfusion with medium containing Ca2+ as well as the time of perfusion with Ca2+ -free medium before inducing Ca2+ paradox. These data indicate that alterations in lysosomal enzymes owing to reinstitution of calcium in Ca2+-deprived hearts may occur as a part of cardiac damage and general cellular disintegration.

Acid Phosphatase↗

PubMed1987

Norepinephrine storage, distribution, and release in diabetic cardiomyopathy.

The ability of hearts to store, distribute, and release norepinephrine (NE) was investigated in rats 8 wk after the induction of diabetes by an injection of streptozotocin (65 mg/kg iv). Chronic diabetes was associated with increased content and concentration of NE in heart and in other tissues such as kidney, brain, and spleen. Reserpine or tyramine treatment resulted in depletion of endogenous cardiac NE in control and diabetic rats. The depletion of NE stores at different times after a dose of reserpine was greater in diabetic hearts. On the other hand, NE stores in diabetic hearts were less sensitive than control hearts to low doses of tyramine but were more sensitive to high doses. The uptake of [3H]NE was greater in diabetic hearts in isolated perfused preparations. In comparison with the control values, diabetic hearts showed a decrease in [3H]NE in the granular fraction and an increase in the supernatant fraction. Diabetic hearts also showed an accelerated spontaneous release of [3H]NE. The increased cardiac NE and the uptake and release of NE in diabetic animals were reversible upon treatment with insulin. These results are consistent with the view that sympathetic activity is increased in diabetic cardiomyopathy and indicate that cardiac NE in diabetic rats is maintained at a higher level partly due to an increased uptake of released NE by adrenergic nerve terminals.

Animals↗

PubMed1987

Sarcolemmal Ca2+ transport in streptozotocin-induced diabetic cardiomyopathy in rats.

Heart sarcolemmal membranes were isolated by the sucrose density gradient method from rats with chronic diabetes induced by a streptozotocin (65 mg/kg iv) injection. Na+-dependent Ca2+-uptake activities were significantly depressed in diabetic sarcolemmal membranes; such alterations were evident at different incubation times and at different concentrations of Ca2+. Administration of insulin to diabetic rats normalized the Na+-dependent Ca2+-uptake activities. ATP-dependent Ca2+ accumulation and Ca2+-stimulated Mg2+-dependent ATPase, which represents Ca2+-pump mechanisms, were significantly depressed in sarcolemmal preparations for diabetic rats and these changes were also reversible upon insulin treatment. An increase in lysophosphatidylcholine and a decrease in phosphatidylethanolamine as well as diphosphatidylglycerol contents were observed in heart membranes isolated from diabetic rats but other phospholipids were unchanged. Cholesterol-to-phospholipid ratio was significantly increased in preparations from diabetic rats. These results indicate a depression in the ability of the cell to remove Ca2+ through Na+-Ca2+ exchange and Ca2+-pump mechanisms in sarcolemma, and these defects may contribute to the occurrence of intracellular Ca2+ overload and diabetic cardiomyopathy.

Adenosine Triphosphate↗

PubMed1987

Altered contractile proteins in skeletal muscle of diabetic rats.

The ATPase activity of myofibrils and myosin from hindlimb muscle was investigated in animals 4 wk after the induction of diabetes by an intravenous injection of streptozotocin (65 mg/kg). Ca2+-stimulated ATPase in myofibrils was increased in diabetic muscle at various times of incubation (1-7 min) as well as at different concentrations of free Ca2+ (10(-7)-10(-5) M Ca2+). Such an increase in Ca2+-stimulated ATPase was evident as early as 1 wk after streptozotocin injection, but Mg2+-ATPase activity remained unaltered. Treatment of diabetic animals with insulin Ca2+-ATPase and actin-activated ATPase activities of pure myosin were similarly increased in diabetic muscle. Myosin ATPase was also activated by K+- or NH4+-EDTA; these responses were more in diabetic muscle. However, sodium dodecyl sulfate gel electrophoresis failed to reveal differences in the patterns of contractile proteins, and pyrophosphate gels did not show significant changes in myosin isozyme patterns between diabetics and controls. The results of this study demonstrate an activation of contractile protein ATPase of skeletal muscle in diabetes and seem to indicate that such an alteration may be responsible for enhanced contractile function of skeletal muscle in this disease.

Actins↗

PubMed1987

Modification of sarcolemmal phosphatidylethanolamine N-methylation during heart hypertrophy.

To evaluate changes in heart sarcolemmal phosphatidylethanolamine (PE) N-methylation, left ventricular hypertrophy was induced in rabbits by banding the abdominal aorta for 4, 8, 14, and 22 wk. The degree of cardiac hypertrophy did not change over the period of time studied. Three catalytic sites involved in the sequential methyl transfer reactions were examined by assaying the incorporation of radiolabeled methyl groups from S-adenosyl-L-methionine (0.055, 10, and 150 microM) into sarcolemmal PE molecules under optimal conditions. Total N-methylation activity at all three sites was significantly increased at 4 wk, unaltered at 8 and 14 wk, and depressed at 22 wk after banding the aorta. Similar biphasic changes were seen for the individual methylated lipid products (monomethylphosphatidylethanolamine, dimethylphosphatidylethanolamine, and phosphatidylcholine) specifically formed at each catalytic site. At all three sites, alterations in PE N-methylation at 22 wk were associated with changes in Vmax values without any change in the apparent affinity for S-adenosyl-L-methionine. In contrast to sarcolemma, a significant increase of the PE N-methylation activity at sites I and III was observed in the sarcoplasmic reticular (microsomal) fraction from 22-wk hypertrophied hearts; the increase in site II was not significant. On the other hand, no changes in the N-methylation activity of the mitochondrial fraction were seen at 22 wk after banding. These findings indicate the occurrence of biphasic alterations in the sarcolemmal PE N-methylation activity during the presence of a stable degree of hypertrophy.

Animals↗

PubMed1987

Sarcolemmal Na+-Ca2+ exchange activity in hearts subjected to hypoxia reoxygenation.

Although the occurrence of intracellular Ca2+ overload is known to be an important factor in hypoxia-reoxygenation injury, the exact mechanisms for this abnormality are not presently clear. Since Na+-Ca2+ exchange in the sarcolemmal membrane is considered to be involved in Ca2+ efflux, this study was undertaken to examine the effect of hypoxia reoxygenation on this system. Isolated rat hearts were made hypoxic by perfusing with a substrate-free medium gassed with 95% N2-5% CO2 and then reperfused with oxygenated normal medium. Hypoxia was found to markedly increase the resting tension and depress the ability of the heart to generate contractile force; reoxygenation resulted in partial recovery of these parameters. Sarcolemmal vesicles were isolated from control, hypoxic, and hypoxia-reoxygenated hearts, and the Na+-dependent Ca2+ uptake activity was measured at different times of incubation as well as at different concentrations of calcium. Sarcolemmal ATP-dependent Ca2+ accumulation was also measured for the purpose of comparison. A significant decrease in Na+-dependent Ca2+ uptake was observed in preparations from hearts made hypoxic for 10 min. Reoxygenation of 10-min hypoxic hearts resulted in a further depression of Na+-Ca2+ exchange activity. ATP-dependent Ca2+ accumulation was also depressed in hypoxic as well as reoxygenated hearts. These results suggest a defect in the Na+-Ca2+ exchange system and the ATP-dependent Ca2+ pump in the heart sarcolemmal membrane, and this may contribute to the occurrence of intracellular Ca2+ overload and functional abnormalities due to hypoxia-reoxygenation injury.

Adenosine Triphosphate↗

PubMed1987

Irreversible damage to sarcolemmal Ca2+ transport in myocardial ischemia.

Perfusion of isolated rat hearts for 10 min with substrate-free hypoxic medium resulted in a depression of sarcolemmal Na+-dependent Ca2+ uptake, Ca2+-stimulated ATPase, ATP-dependent Ca2+ uptake and Na+-K+ ATPase in sarcolemma. Reoxygenation of these hearts resulted in a further depression of all these activities. Na+-induced Ca2+-efflux was unaffected in vesicles of hearts subjected to hypoxia-reoxygenation. Developed contractile force and resting tension in hypoxic hearts were 15% and 400% of control values, respectively, while reoxygenation was associated with a slight recovery of developed contractile force and the resting tension was lowered appreciably but remained elevated. Because sarcoplasmic reticular Ca2+ uptake and mitochondrial Ca2+ uptake were depressed under similar conditions, cellular injury due to hypoxia-reoxygenation was not specific to the sarcolemma. These results indicate that inability of the ischemic heart to recover its function may be associated with defects in Ca2+-transport systems.

Animals↗

PubMed1987

Pathophysiological aspects of myocardial hypertrophy.

Heart hypertrophy in response to increased workload is a complex process in which this organ adapts to the environment by increasing the muscle mass in terms of additional contractile units and formation of different types of contractile proteins (myosin isozymes). In addition, augmentation of membrane function with respect to calcium transport activities of sarcolemma and sarcoplasmic reticulum occurs at early stages of cardiac hypertrophy associated with hyperfunction of the myocardium. However, if cardiac hypertrophy is left unattended beyond a certain period, physiological hypertrophy is converted to pathological hypertrophy whereby the cardiac muscle is unable to generate an adequate amount of contractile activity. It appears that the sympathetic nervous system is activated for producing beneficial effects at early stages but an elevated level of sympathetic tone for a prolonged period could result in dysfunction of the cardiac muscle. The transition of physiological hypertrophy to pathological hypertrophy seems to be due to the occurrence of intracellular calcium overload in the myocardial cell as a consequence of defects in the membrane calcium transport systems. It is suggested that careful attention should be paid not only to removal of the stimulus responsible for cardiac hypertrophy but also to lowering sympathetic tone. Efforts should also be made to prevent the occurrence of intracellular calcium overload due to membrane defects.

Animals↗

PubMed1986

Stimulation of Na+-Ca2+ exchange in heart sarcolemma by insulin.

Insulin was found to stimulate Na+-dependent Ca2+ uptake in dog heart sarcolemma in a concentration dependent manner (0.001 to 1 milliunits/ml). Maximal stimulation (160 to 170%) was seen at 0.1 to 1 milliunits/ml of insulin. Unlike Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake was unaltered by 1 microunit/ml of insulin. However, high concentrations of insulin (0.01 to 1 milliunits/ml) significantly increased the ATP-dependent Ca2+ uptake activity of heart sarcolemma; maximal increase (60%) was observed at 1 milliunit/ml of insulin. The Na+ K+-ATPase activity did not change upon incubating sarcolemma with insulin. The membrane preparation exhibited specific insulin binding characteristics. The Scatchard plot analysis of the data indicated two binding sites for insulin; the association constants for the high and low affinity sites were 2 X 10(9) M-1 and 4.4 X 10(8) M-1, respectively. These results support the view regarding the presence of insulin receptors in the heart cell membrane and indicate a dramatic effect of insulin on the sarcolemmal Ca2+ transport systems.

Animals↗