title: Protein kinase A does not alter unloaded velocity of sarcomere shortening in skinned rat cardiac trabeculae.
abstract: Whether beta-adrenergic stimulation affects the cross-bridge cycling rate independently of its effect on Ca2+ handling by the cardiac myocyte is still unknown. An increase in cross-bridge cycling rate may result in increased unloaded velocity of sarcomere shortening (V0). To test this hypothesis directly, skinned rat cardiac trabeculae were attached between a silicon strain gauge (approximately 3.5 kHz resonant frequency) and a fast displacement motor. V0 was measured by a modified "Edman slack test" during a single maximal activation using seven to eight sarcomere-length step releases (measured by laser diffraction) ranging between 0.12 and 0.20 micron (15.0 +/- 0.1 degrees C). beta-Adrenergic stimulation was mimicked by exposing the trabeculae to the catalytic subunit of protein kinase A (PKA). Treatment with PKA (3 micrograms/ml; 45 min) caused a significant (P < 0.01) increase (41 +/- 13%) in the Ca2+ concentration required for half-maximal steady-state tension development. Neither maximum tension nor V0 was affected by treatment with PKA, suggesting that beta-adrenergic stimulation does not affect the rate-limiting step of cross-bridge cycling during unloaded shortening in myocardium.
authors.affiliation: Department of Physiology and Biophysics, University of Illinois at Chicago 60607-7171, USA.
authors.forename: P M
authors.initials: PM
authors.lastname: Janssen
authors.forename: P P
authors.initials: PP
authors.lastname: de Tombe
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003238:Connective Tissue / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D009200:Myocardial Contraction; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D012044:Regression Analysis; D012518:Sarcomeres / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D011943:Receptors, Adrenergic, beta; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium