Effects of combined use of class I antiarrhythmic agents on V max of guinea-pig ventricular muscles

1991 ◽  
Vol 5 (S4) ◽  
pp. 801-804
Author(s):  
Junji Toyama ◽  
Takashi Kawamura ◽  
Itsuo Kodama
Keyword(s):  
Guinea Pig ◽  
Class I ◽  
Antiarrhythmic Agents ◽  
Combined Use

Class I antiarrhythmic drug effects on ouabain binding to guinea pig cardiac Na+-K+ATPase

1999 ◽  
Vol 77 (11) ◽  
pp. 866-870 ◽  
Author(s):  
Abdulrahman A Almotrefi ◽  
Chona Basco ◽  
Azadali Moorji ◽  
Nduna Dzimiri
Keyword(s):  
Guinea Pig ◽  
Drug Effects ◽  
Receptor Occupancy ◽  
Class I ◽  
Antiarrhythmic Agents ◽  
Binding Assays ◽  
Ouabain Binding ◽  
Guinea Pig Heart ◽  
Receptor Sites ◽  
Displacement Assays

The notion that the inhibition of the Mg2+-dependent ATP-hydrolytic function of the myocardial Na+-K+ATPase by class I antiarrhythmic agents occurs as a result of their binding to the same receptor sites as the digitalis glycosides was tested by performing competitive binding assays of [3H]ouabain (OUA) with eight drugs: disopyramide, encainide, lidocaine, lorcainide, phenytoin, procainamide, quinidine, and tocainide in guinea pig heart microsomal preparations. In the first set of experiments, 10-200 µM concentrations of the drugs were preincubated with the enzyme and displacement assays performed with 250 nM OUA. The drugs showed receptor occupancy of 19-32% at 50 µM, 25-44% at 100 µM, and 37-56% at 200 µM. Then, 10-500 nM concentrations of OUA were preincubated with the enzyme, and competitive assays were performed using 200 µM concentrations of the drugs. OUA occupied 39-51% of the receptor sites at 100 nM, 44-67% at 250 nM, and 62-82% at 500 nM, displacing the drugs in a concentration-dependent fashion. The results show that antiarrhythmic drugs interact with the same or similar receptor sites as ouabain on the Na+-K+ATPase, pointing to a possible contribution of these interactions to the mechanism for their inhibitory actions on the enzyme, and perhaps their arrhythmogenic effects.Key words: class I antiarrhythmic agents, proarrhythmias, Na+-K+ATPase, ouabain binding.

scholarly journals Identification of a novel type 2 fiber population in mammalian skeletal muscle by combined use of histochemical myosin ATPase and anti-myosin monoclonal antibodies.

1990 ◽  
Vol 38 (2) ◽  
pp. 257-265 ◽  
Author(s):  
L Gorza
Keyword(s):  
Monoclonal Antibodies ◽  
Guinea Pig ◽  
Atpase Activity ◽  
High Activity ◽  
Skeletal Muscles ◽  
Enzyme Histochemistry ◽  
Myosin Atpase ◽  
Myosin Atpase Activity ◽  
Combined Use

A novel type of myosin heavy chain (MHC), called 2X, has been recently identified in type 2 fibers of rat skeletal muscles using an immunochemical approach. In the present study, the same panel of anti-MHC monoclonal antibodies was used in immunohistochemistry combined with enzyme histochemistry to identify and compare type 2X fibers in hindlimb skeletal muscles of rat, mouse, and guinea pig. Immunohistochemistry shows that 2X MHC is localized in a large subset of type 2 fibers and is co-expressed with 2A or 2B MHC in a small number of fibers. Enzyme histochemistry shows that type 2X fibers display low myosin ATPase activity after pre-incubation at pH 4.3 and high activity after paraformaldehyde pre-incubation at pH 10.4. After pre-incubation at pH 4.6, myosin ATPase shows intermediate and high activity in rat and mouse 2X fibers, respectively, whereas it is low in guinea pig 2X fibers. Succinate dehydrogenase displays moderate to high activity in 2X fibers of all species. Taken together, these staining patterns allow this novel fiber population to be distinguished from the other type 2 fibers using only enzyme histochemistry. Nevertheless, the combined use of immuno- and enzyme histochemistry prevents incorrect fiber typing due to the interspecies variability of myosin ATPase activity among the correspondent fiber types, and completely modifies the presently used classification of mouse type 2 fibers.

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