Factors Affecting the Calcium Sensitivity of the Contractile Proteins of the Heart

Lamont, Christine (1987) Factors Affecting the Calcium Sensitivity of the Contractile Proteins of the Heart. PhD thesis, University of Glasgow.

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Abstract

Force production by cardiac muscle can be altered by changing either the calcium available to the contractile proteins or their sensitivity to calcium. The work of this thesis principally concerns an investigation of factors affecting the calcium sensitivity of the contractile proteins of cardiac muscle . The calcium sensitivity of the contractile proteins was examined using chemically-skinned muscle mainly from rat heart. Completely and partially skinned preparations were used. The completely chemically-skinned preparations had their cellular membranes disrupted by exposure to the non-ionic detergent Triton-X100. This should leave the isolated contractile proteins in their physiological configuration. The second type of preparation uses saponin-treatment. Saponin is an agent which precipitates cholesterol molecules from membranes. As the sarcolemma is richer in cholesterol than the subcellular membranes, brief exposure of preparations to saponin punctures the sarcolemma while leaving the subcellular membranes intact and functional. In both types of preparation the 'intracellular' conditions are under experimental control since the bathing solution is effectively an extension of the sarcoplasm. These preparations can be used to establish the relationship between 'intracellular' calcium and tension by measuring the tension produced at a range of free calcium concentrations. Four general aspects of the calcium sensitivity of the contractile proteins were investigated, (1) hysteresis in the calcium sensitivity of cardiac muscle, (2) the changes in calcium sensitivity with sarcomere length, (3) the effect of altering myofilamental lattice spacing by hypertonic shrinkage and (4) the effect of imidazole-containing compounds on calcium sensitivity Chapter 1 and 2 report on an investigation of the hysteresis in, and the length dependence of, the pCa-tension relationship. Hysteresis means that a muscle can maintain a higher tension level than it can create de novo at any free calcium level. This phenomenon has only been reported in skeletal muscle to dates this thesis provides the first evidence for hysteresis in heart muscle. It is proposed that hysteresis is a special manifestation Of the length-dependence of calcium sensitivity. The calcium sensitivity of the contractile protein's increases as the sarcomere length is increased. I propose that both phenomenon are the result of reduced myofilament separation (i) brought about in the case of hysteresis by force production and (ii) by the change in length in the case of length-dependence of Ca-sensitivity. Experiments designed to test this proposal are described in chapter 2. Lattice spacing was altered independently of force production or sarcomere length change by the use of hypertonic shrinkage techniques. This technique involves addition of long chain polymers (Dextran M. Wt. >40,000) to the bathing solutions.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physiology
Date of Award: 1987
Depositing User: Enlighten Team
Unique ID: glathesis:1987-77591
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 09:04
Last Modified: 14 Jan 2020 09:04
URI: http://theses.gla.ac.uk/id/eprint/77591

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