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Lack of correlation of electrocardiographic and morphologic changes followingnorep inephrine or isoproterenol infusions in dogs
J Mol Cell Cardiol 18 (Supplement 3) (1986) LACK OF CORRELATION OF ELECTROCARDIOGRAPHIC AND MORPHOLOGIC CHANGES FOLLOWING NOREPINEPHRINE OR ISOPROTERENOL INFUSIONS IN DOGS. G. Todd, H. Spangler. Department of Anatomy, University of Nebraska Medical Center, Omaha, NE, U.S.A. Catecholamine excess results in characteristic contraction band (CB) lesions of myocardial cells, but less is known about its effects on electrocardiographic changes. This study was undertaken to correlate the development of CB lesions with the appearance of ECG changes during norepinephrine (NE) or isoproterenol (ISP) infusions. Forty-five dogs were continuously infused for up to 1 hour with saline, NE (4 ug/kg/min) or ISP (2.5 ug/kg/min). The majority of the controls exhibited a normal sinus rhythm while a few had sinus tachyeardia (160-170 bpm) throughout the infusion. Within 1-2 min 69% of the NE-treated dogs exhibited frequent PVC's or runs of ventricular tachycardia. Despite continued infusion, the ECG's reverted to a sinus tachycardia by i0 min. ISP-treated dogs exhibited infrequent PVC's, but instead exhibited a significant ST segment depression after 5 min which persisted throughout the infusion. Despite the diversity of ECG and hemodynamic changes, the two catecholamines produced morpholgically identical CB lesions in comparable numbers at these two infusion rates. Thus, the underlying pathophysiology of this distinct form of myocardial necrosis appears more complex and lacks any temporal correlation with the concomitant ECG abnormalities.
A CHANGE IN ACTION POTENTIAL DURATION DOES NOT UNDERLIE THE NEGATIVE CHRONOTROPIC EFFECT OF ACETYLCHOLINE ON RABBIT S.A.NODE. O.Tripathi, A.Bhatnagar. Pharmacology Division, Central Drug Research Institute, Lucknow, India. Acetylcholine (ACh) increases gK in pacemaker cells (PC), causes hyperpolarisation and is believed to shorten action potential duration (APD). As no report exists about ACh induced changes in APD in PC, it was studied on isolated rabbit SA node (Tyrode~ K + 5.4 raM, pH 7.4, 37oc; AP recorded by glass microelectrodes), to assess its role in negative chronotropic effect (NCE) of ACh. ACh (10-8 - 10-5 M) increased maximum diastolic potential, upstroke velocity (V~ax) , and cycle length (CL) and reduced the velocity of diastolic depolarisation (DD, V~ax) , the threshold potential (TP) remaining unaltered. APD at -40 mV (APD40) and at 90% repolarisation (APD90) was increased by ACh. Eserine potentiated and atropine blocked these effects. The 'effective'l-V curves during repolarisation were shifted to lower (at 0 to -30 mV) and higher (at -35 to -55 mV) values suggesting changes in net current flow, the membrane condactance being increased negative to -30 mV. Since IK triggers repolarisation and is involved in initial part of DD, ACh is suggested to increase a late IK leading to hyperpolarisation, and reduce V~a x taking longer to bring the cell to TP, which was unaltered. Consequent increase in CL caused a NCE. Increase in V~a x made insignificant contribution to NCE. Increase in APD40 and APD90 by ACh in PC, unlike their reduction in atrial cells,points to significant differences in its action on these cells.
SUBC~ELLD3L/kRDISIILIBIFrlON. ISOI~TION~UqD C g ~ E R A C ~ I ~ T I O N OF C~kI~I~RIkIO~EI./LI~FA~Rq[ST RECEPTOR FROM RABBIT CARDIAC MUSCLE. B.S. Tuana, B. Murphy, Q. Yi. Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada M5S IAS. The binding of [3H]nitrendlplne (N), [3H]PN 200-110 (P) and [3H]verapamil (V) was studied in purified sarcolemma ( ~ ) , sarcoplasmlc retlculum (SR) and mltoehondria (MIT). The density distribution of drug binding sites correlated wlth Na+-K+ATPase and Na+-Ca 2+ exchanger (~h) and differed from phospholamban and oxalate supported Ca 2+ uptake (SR) and azlde sensitive ATPase ( ~ T ) . The binding characteristics of SL receptor sites (K D = 0.3 nM (N), 0.2 nM (P), 4.1 nM (V) and B x 0.5 - 1.0 pmol/mg protein) were unaltered by reducing agents or membrane phospm~orylation. The SL receptor was solubilized in chaps and purified by affinity chromatography on lectiu columns. The receptor sites for (N), (P) and (V) co-purlfled together and on analysis by SDS-PAGE indicated the enrichment in proteins of Mr 130-140 kDa, 90-100 kDa and 4555 kDa. The isolated receptor contained no intrlnslc kinase activity although the phosphorylatlon of a 53 kDa protein was observed in the presence of cAMP-protein kiuase. These results indicate that the receptor sites for (N), (P) and (V) are of SL origin and eopurify together suggesting that they are localized in the same protein or subunits of the same structure, cAMP-dependent phosphorylatlon of the 53 kDa protein may play an important role in the regulation of the calcium channel. (Supported by Ontario Heart and Stroke Foundation).
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A CHANGE IN ACTION POTENTIAL DURATION DOES NOT UNDERLIE THE NEGATIVE CHRONOTROPIC EFFECT OF ACETYLCHOLINE ON RABBIT S.A.NODE. O.Tripathi, A.Bhatnagar. Pharmacology Division, Central Drug Research Institute, Lucknow, India. Acetylcholine (ACh) increases gK in pacemaker cells (PC), causes hyperpolarisation and is believed to shorten action potential duration (APD). As no report exists about ACh induced changes in APD in PC, it was studied on isolated rabbit SA node (Tyrode~ K + 5.4 raM, pH 7.4, 37oc; AP recorded by glass microelectrodes), to assess its role in negative chronotropic effect (NCE) of ACh. ACh (10-8 - 10-5 M) increased maximum diastolic potential, upstroke velocity (V~ax) , and cycle length (CL) and reduced the velocity of diastolic depolarisation (DD, V~ax) , the threshold potential (TP) remaining unaltered. APD at -40 mV (APD40) and at 90% repolarisation (APD90) was increased by ACh. Eserine potentiated and atropine blocked these effects. The 'effective'l-V curves during repolarisation were shifted to lower (at 0 to -30 mV) and higher (at -35 to -55 mV) values suggesting changes in net current flow, the membrane condactance being increased negative to -30 mV. Since IK triggers repolarisation and is involved in initial part of DD, ACh is suggested to increase a late IK leading to hyperpolarisation, and reduce V~a x taking longer to bring the cell to TP, which was unaltered. Consequent increase in CL caused a NCE. Increase in V~a x made insignificant contribution to NCE. Increase in APD40 and APD90 by ACh in PC, unlike their reduction in atrial cells,points to significant differences in its action on these cells.
SUBC~ELLD3L/kRDISIILIBIFrlON. ISOI~TION~UqD C g ~ E R A C ~ I ~ T I O N OF C~kI~I~RIkIO~EI./LI~FA~Rq[ST RECEPTOR FROM RABBIT CARDIAC MUSCLE. B.S. Tuana, B. Murphy, Q. Yi. Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada M5S IAS. The binding of [3H]nitrendlplne (N), [3H]PN 200-110 (P) and [3H]verapamil (V) was studied in purified sarcolemma ( ~ ) , sarcoplasmlc retlculum (SR) and mltoehondria (MIT). The density distribution of drug binding sites correlated wlth Na+-K+ATPase and Na+-Ca 2+ exchanger (~h) and differed from phospholamban and oxalate supported Ca 2+ uptake (SR) and azlde sensitive ATPase ( ~ T ) . The binding characteristics of SL receptor sites (K D = 0.3 nM (N), 0.2 nM (P), 4.1 nM (V) and B x 0.5 - 1.0 pmol/mg protein) were unaltered by reducing agents or membrane phospm~orylation. The SL receptor was solubilized in chaps and purified by affinity chromatography on lectiu columns. The receptor sites for (N), (P) and (V) co-purlfled together and on analysis by SDS-PAGE indicated the enrichment in proteins of Mr 130-140 kDa, 90-100 kDa and 4555 kDa. The isolated receptor contained no intrlnslc kinase activity although the phosphorylatlon of a 53 kDa protein was observed in the presence of cAMP-protein kiuase. These results indicate that the receptor sites for (N), (P) and (V) are of SL origin and eopurify together suggesting that they are localized in the same protein or subunits of the same structure, cAMP-dependent phosphorylatlon of the 53 kDa protein may play an important role in the regulation of the calcium channel. (Supported by Ontario Heart and Stroke Foundation).
71