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Kinetic model for binding of dihydropyridine calcium channel antagonists to cardiac sarcolemmal membranes
18 THE DEVELOPMENTAND REVERSAL OF HYPERTHYROID CARDIOMEGALY IN ADULT RATS; STRUCTURAL CHANGES IN MYOCYTESTHAT PERSIST. M. Gerdes, J. Hines, S. Bishop, J. Kriseman. Dept. of Anatomy, Univ. of South F l o r i d a , Tampa, FL and Dept. of Pathology, Univ. of Alabama in Birmingham, Birmingham, AL. Adult female rats were treated in the f o l l o w i n g manner (n > 6 f o r each group): l ) fed 0,6% desiccated t h y r o i d (T) f o r lO weeks; 2) controls (CT~ f o r T; 3) fed T f o r lO weeks then no T f o r 3 months (R); 4) controls (CR) f o r R, Oxygen consumption increased 86%, heart rate 24%, and s y s t o l i c blood pressure 29% in T compared to CT. I s o l a t e d cardiac myocytes were prepared by retrograde coronary perfusion with collagenase, Cell lengths (L) were measured d i r e c t l y and cell volumes (V) were determined with a Coulter Channelyzer system f o r r i g h t (RV) and l e f t v e n t r i c u l a r (LV) myocytes. Heart weight increased 44% in T compared to CT and remained 22% l a r g e r in R compared to CR. Body weights of treated animals varied < 7% (NS) from t h e i r c o n t r o l s . Both RV and LV myocyte L increased 15% in T compared to CT and remained ll% longer in R compared to CR V increased I0% in LV and 29% in RV of T compared to CT. V of LV and RV myocytes from R and CR were s i m i l a r . Calculated number of v e n t r i c u l a r myocytes was increased 21% in T compared to CT and 26% in R compared to CR. We concluded t h a t T increased L and V and that L changes p e r s i s t a f t e r the reversal of hyperthyroidism. Approximately h a l f of the heart enlargement is due to hyperplasia of myocytes, and t h i s increased number is retained in R r e s u l t i n g in the incomplete reversal of heart mass. CONSIDERATION FOR YOUNG INVESTIGATOR COMPETITION
AORTIC PRESSURE AFFECTS PROTEIN DEGRADATION, INDEPENDENT OF INTRAVENTRICULAR PRESSURE, CONTRACTILITY, AND PROSTAGLANDINS. E. E. Gordon, Y. Kira, H. E. Morgan. Physiology Dept., The Pennsylvania State Univ., Hershey, PA 17033 The effect of increased aortic pressure on rates of protein degradation (PDR) was studied in Langendorff perfused rat hearts subjected to various states of mechanical activity. First and second hour PDR were measured in beating hearts, beating hearts in which the left ventricle was drained, and in hearts that were drained and arrested with tetrodotoxin. In hearts supplied glucose, an increase in aortic perfusion pressure from 60 to 120 mmHg resulted in a decrease in second hour PDR (25%) but was accompanied by a decrease in ATP and creatine-P (CP) in the drained and arresteddrained conditions. To exclude energy depletion as the cause of the decrease in second hour PDR seen at higher pressure, hearts were perfused under similar conditions but supplied with pyruvate as substrate. In all conditions, CP increased while second hour PDR decreased. Varying calcium concentration of the perfusate did not alter the effect of pressure on second hour PDR, however, ATP and CP decreased. Also, addition of the cyclooxygenase inhibitor indomethacin did not alter the effect of higher pressure on second hour PDR nor did it alter ATP and CP. Thus, increased aortic perfusion pressure decreased PDR in the second hour by a mechanism that was not mediated by intraventricular pressure, contractility, energy availability, or prostaglandins. Mediation by calcium could not be ruled out due to the accompanying decrease in ATP and CP.
Herbette, LGI-3, Vant Erve. ~ , Sarmiento, J~,Rhodes, DG 1,3 and Katz. A ~ . Kinetic Model for Binding of Dihydropyridine C a l c i ~ Channel Antagonists to Cardiac SarcoleI[mal Membranes. Depts. of Medicine I and Biochem. 2, Univ. Conn., Farmington, Cf, and Biology Dept. 3, Brookhaven Natl. Lab., Upton, N.Y. Differential scanning calorimetry showed that dihydropyridine c a l c i ~ channel antagonists were very soluble in synthetic membrane lipids. At concentrations of antagonist in the range 10-11 to 1 0 ~ M, the molar ratio of antagonist to canine cardiac s a r c o l ~ lipid, measured by a centrifugation assay, was linearly dependent on drug concentration. Using these curves and ass~ning that all of the antagonist partitioned into the sarcolenm~l lipid bilayer, partition coefficients between 1.000-40,000 were calculated for several dihydropyridines. The intrinsic on-rate constant for an antagonist with a partition coefficient >20,000 was approximately 107 (M sec)-I , compared to 106 (M sec)-I for antagonists with partition coefficients in the range 1.000-15.000. Lamellar meridiosal x-ray ~nd neutron diffraction studies have shown that two of these antagonists penetrate 15 A into the lipid bilayer region (hydrocarbon core) of non-receptor membranes. These observations suggest that these lipid-soluble antagonists may "locate" their protein receptors by first partitioning into the membrane lipid bilayer and then diffusing laterally through the bilayer to the reoeptor site(s). Such a mechani~ may provide n~lecular criteria for the design of new calciu~ channel antagonists with irmproved clinical performance.
AORTIC PRESSURE AFFECTS PROTEIN DEGRADATION, INDEPENDENT OF INTRAVENTRICULAR PRESSURE, CONTRACTILITY, AND PROSTAGLANDINS. E. E. Gordon, Y. Kira, H. E. Morgan. Physiology Dept., The Pennsylvania State Univ., Hershey, PA 17033 The effect of increased aortic pressure on rates of protein degradation (PDR) was studied in Langendorff perfused rat hearts subjected to various states of mechanical activity. First and second hour PDR were measured in beating hearts, beating hearts in which the left ventricle was drained, and in hearts that were drained and arrested with tetrodotoxin. In hearts supplied glucose, an increase in aortic perfusion pressure from 60 to 120 mmHg resulted in a decrease in second hour PDR (25%) but was accompanied by a decrease in ATP and creatine-P (CP) in the drained and arresteddrained conditions. To exclude energy depletion as the cause of the decrease in second hour PDR seen at higher pressure, hearts were perfused under similar conditions but supplied with pyruvate as substrate. In all conditions, CP increased while second hour PDR decreased. Varying calcium concentration of the perfusate did not alter the effect of pressure on second hour PDR, however, ATP and CP decreased. Also, addition of the cyclooxygenase inhibitor indomethacin did not alter the effect of higher pressure on second hour PDR nor did it alter ATP and CP. Thus, increased aortic perfusion pressure decreased PDR in the second hour by a mechanism that was not mediated by intraventricular pressure, contractility, energy availability, or prostaglandins. Mediation by calcium could not be ruled out due to the accompanying decrease in ATP and CP.
Herbette, LGI-3, Vant Erve. ~ , Sarmiento, J~,Rhodes, DG 1,3 and Katz. A ~ . Kinetic Model for Binding of Dihydropyridine C a l c i ~ Channel Antagonists to Cardiac SarcoleI[mal Membranes. Depts. of Medicine I and Biochem. 2, Univ. Conn., Farmington, Cf, and Biology Dept. 3, Brookhaven Natl. Lab., Upton, N.Y. Differential scanning calorimetry showed that dihydropyridine c a l c i ~ channel antagonists were very soluble in synthetic membrane lipids. At concentrations of antagonist in the range 10-11 to 1 0 ~ M, the molar ratio of antagonist to canine cardiac s a r c o l ~ lipid, measured by a centrifugation assay, was linearly dependent on drug concentration. Using these curves and ass~ning that all of the antagonist partitioned into the sarcolenm~l lipid bilayer, partition coefficients between 1.000-40,000 were calculated for several dihydropyridines. The intrinsic on-rate constant for an antagonist with a partition coefficient >20,000 was approximately 107 (M sec)-I , compared to 106 (M sec)-I for antagonists with partition coefficients in the range 1.000-15.000. Lamellar meridiosal x-ray ~nd neutron diffraction studies have shown that two of these antagonists penetrate 15 A into the lipid bilayer region (hydrocarbon core) of non-receptor membranes. These observations suggest that these lipid-soluble antagonists may "locate" their protein receptors by first partitioning into the membrane lipid bilayer and then diffusing laterally through the bilayer to the reoeptor site(s). Such a mechani~ may provide n~lecular criteria for the design of new calciu~ channel antagonists with irmproved clinical performance.