Steady-state isometric contractile properties of cultured strands of neonatal Rattus norvegicus (Sprague-Dawley strain) cardiac muscle

Chockalingam, Arunachalam (1982) Steady-state isometric contractile properties of cultured strands of neonatal Rattus norvegicus (Sprague-Dawley strain) cardiac muscle. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Although the mechanical properties of cardiac muscle have been studied in various preparations, no direct measurement of isometric tension has been made at the cellular level. In this study, cultured strands of neonatal rat cardiac muscle were attached to a microgramme force transducer, using a non-traumatic method to obtain direct measurement of isometric tension. -- The isometric mechanical properties of the cultured myocardial strands were studied during spontaneous and electrically-stimulated contractions at different lengths, temperatures and rates of stimulation. Steady-state inotropic and chronotropic responses to independent manipulation of external ionic concentration of K⁺, Ca⁺⁺ and Na⁺ as well as simultaneous manipulation of Na⁺ and Ca⁺⁺ were studied. Cholinergic and adrenergic receptor response was characterized using appropriate pharmacologic agonists and antagonists. -- The basic mechanical properties observed included length-tension relationship, force-frequency response and effects of temperature. Total amount of strand stretch required to describe the complete length-tension relationship was only ± 1% of the optimum length, Lmax; suggesting that cultured strands are stiffer than adult rat papillary muscle. Repeating length-tension measurements in the same strand showed an absence of hysteresis. All other mechanical properties were similar to those observed for intact adult rat papillary muscle. Spontaneous contraction rate was influenced by K⁺ and Na⁺, while Na⁺ and Ca⁺⁺ influenced contractility. The interaction between Na⁺ and Ca⁺⁺ was very striking; the observations were consistent with the function of a sodium-calcium exchange carrier. The strand was shown to possess cholinergic muscarinic receptors, which regulate only spontaneous rate and beta-adrenergic receptors which regulate both rate and contractility. -- Thus, in the strand, functional properties of various regions of the heart are represented in a single preparation. The physiological characteristics were highly reproducible between and within strand preparations. Except for the fact that the strand is fragile and de-differentiated, it represents an accurate model for myocardial physiology and offers some important advantages for investigation of cellular physiology and the influence of ionic and drug manipulations on its basic physiology.

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