Effects of magnesium and calcium upon excitation-contraction coupling in the heart
type: CreativeWork
description: Calcium (Ca2 ) availability to cardiac myofilaments is the primary factor determining the force of cardiac contraction. An intracellular organelle, the sarcoplasmic reticulum (SR), regulates the relaxation of the muscle as well as acting as a source of activating Ca2 during excitation-contraction coupling. Calcium metabolism in the heart undergoes developmental changes during early postnatal life and some of these changes may concern the activity of the SR. Using the technique of oxalate-supported Ca2 uptake into SR vesicles from rat hearts, the developmental changes in the activity of the SR Ca21 ATPase pump which regulates cardiac relaxation was monitored. It was observed that there occurred an increase in Call uptake with postnatal age in 3 strains of rat (Wistar, the Spontaneously Hypertensive Rat, SI-IR, and the Wistar- Kyoto, WKY, normotensive counterpart to the SHR). Additionally, age-related changes in the activity of an SR membrane protein, phospholamban (PLB), were investigated. Phospholamban phosphorylation increases the rate of Ca 2 uptake into the SR and it was observed that PLB phosphorylation in all 3 strains also increases with postnatal age. There seems then to be a coordinate relationship between the amount of PLB phosphorylated in the developing heart and the activity of the Ca 2 uptake mechanism immediately after birth in rats. When the SR is functionally immature in this very early postnatal period, the relative contribution to Ca 2 metabolism of another system, the sarcolemmal sodium/calcium exchanger, may be increased. In fact it was observed that when SR Ca 2 uptake is low the exchanger displays a heightened level of activity which may serve as a compensatory mechanism in maintaining intracellular Ca2 levels. Magnesium (Mg2 ) has, until recently, been thought to be present within the cell at levels which preclude it from having a regulatory role in cardiac function. New evidence suggests that Mg 2 may be present in cardiac cells at levels whi…
abstract: Calcium (Ca2 ) availability to cardiac myofilaments is the primary factor determining the force of cardiac contraction. An intracellular organelle, the sarcoplasmic reticulum (SR), regulates the relaxation of the muscle as well as acting as a source of activating Ca2 during excitation-contraction coupling. Calcium metabolism in the heart undergoes developmental changes during early postnatal life and some of these changes may concern the activity of the SR. Using the technique of oxalate-supported Ca2 uptake into SR vesicles from rat hearts, the developmental changes in the activity of the SR Ca21 ATPase pump which regulates cardiac relaxation was monitored. It was observed that there occurred an increase in Call uptake with postnatal age in 3 strains of rat (Wistar, the Spontaneously Hypertensive Rat, SI-IR, and the Wistar- Kyoto, WKY, normotensive counterpart to the SHR). Additionally, age-related changes in the activity of an SR membrane protein, phospholamban (PLB), were investigated. Phospholamban phosphorylation increases the rate of Ca 2 uptake into the SR and it was observed that PLB phosphorylation in all 3 strains also increases with postnatal age. There seems then to be a coordinate relationship between the amount of PLB phosphorylated in the developing heart and the activity of the Ca 2 uptake mechanism immediately after birth in rats. When the SR is functionally immature in this very early postnatal period, the relative contribution to Ca 2 metabolism of another system, the sarcolemmal sodium/calcium exchanger, may be increased. In fact it was observed that when SR Ca 2 uptake is low the exchanger displays a heightened level of activity which may serve as a compensatory mechanism in maintaining intracellular Ca2 levels. Magnesium (Mg2 ) has, until recently, been thought to be present within the cell at levels which preclude it from having a regulatory role in cardiac function. New evidence suggests that Mg 2 may be present in cardiac cells at levels whi…
author: Freestone, Nicholas
language: en
keywords: F100 - Chemistry
date published: 1995-06
date modified: 2026-07-24T01:36:13Z
provider: University of Central Lancashire
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Central Lancashire