Membrane potential oscillations in enzymatically isolated rat myocardial cells

Effects of procaine and caffeine on the contractility of enzymatically isolated myocytes and intact cardiac tissue

1. Procaine and caffeine exerted opposite effects on the contractility of rat cardiac tissue. 2. Procaine enhanced and caffeine depressed isometric contractile force of right ventricular strips. 3. In enzymatically isolated cells, caffeine increased the frequency and decreased the amplitude of spontaneous contractions, while procaine retarded the beating rate but concomitantly raised the shortening amplitude of the myocyte. 4. Both drugs depressed the propagation velocity of the contractile waves. 5. The results are suggested to be due to the opposite effects of the two drugs on the Ca-release process of the sarcoplasmic reticulum.

Isolation and characterization of single myocardial cells from the quail, Coturnix coturnix japonica

1. The enzymatic cell isolation technique was applied to the bird heart resulting in myocytes of which 10-50% maintained their spindle-shaped morphology, excluded the vital dye, Evans blue and tolerated physiological concentration of Ca2+ ions. 2. The length of spindle-shaped myocytes was on average 289 +/- 7 microns, and the maximum width was 10.2 +/- 0.3 microns. The mean length of the sarcomeres was 2.18 +/- 0.03 microns. 3. In electron micrographs the fine structure of the spindle-shaped myocytes looked normal--regular sarcomeric organization with clear A and I bands, mitochondria with tightly located cristae and well-developed sarcoplasmic reticulum (SR). 4. Most (80%) of the spindle-shaped myocytes were quiescent in physiological calcium concentration and practically all of them could be induced to twitch by electric field stimulation. Some beat spontaneously showing mostly slowly-propagating (135 +/- 6 microns/sec at 20 degrees C) contraction waves, so-called phasic contractions. Sometimes spontaneous twitch-type contractions could also be seen.

Isolation and characterization of single myocardial cells from the perch, Perca fluviatilis

In applying the enzymatic cell isolation technique to the fish heart about 40% of the dispersed myocytes maintained their spindle-shaped morphology, and about half of them tolerated physiological concentration of Ca2+ and excluded the vital dye, Evans blue. The length of spindle-shaped myocytes was on average 133 +/- 3 micron and the maximum width was 4.2 +/- 0.1 micron. The mean length of the sarcomeres was 2.1 +/- 0.1 micron. The sizes of the myocytes did not vary significantly with the weights of the fish. Electron microscopic examinations showed typical fish myocardial cell structure; absence of transverse tubule system, a sparse network of sarcoplasmic reticulum and from a few up to eight or more myofibrils. The cells were mononuclear. Most of the Ca2+-tolerant myocytes were quiescent, but the contraction in them could be induced by electric field stimulation. Both the spontaneous and electrically triggered contractions were of twitch type. The slowly propagating contraction waves, so-called phasic contractions common in isolated mammalian cardiac myocytes, could not be seen at all.

Activation of contractility and sarcolemmal Ca2+-ATPase by Ca2+ during postnatal development of the rat heart

The effects of 0.25-16.0 mM Ca2+ on the contractile force of isolated ventricular strips and sarcolemmal Ca2+-ATPase activity during postnatal development of the rat heart were studied. The half maximal concentrations for contractile activation of ventricular strips were 0.76 and 5.59 mM Ca2+ for adult and 3-day-old rats, respectively. The sensitivity towards Ca2+ began to change from newborn type to that of adult rat 2 weeks after birth and was almost completed after 4 weeks. No significant differences were found in half maximal activation of Ca2+-ATPase by Ca2+ between different age groups. Activation of contractility and Ca2+-ATPase by Ca2+ were linearly related in 30-day-old and adult rats but not in 3- and 10-day-old rats. The observed sensitivity change towards extracellular Ca2+ for contractile activation is suggested to be due to the development of transverse tubular system and sarcoplasmic reticulum during the first 4 weeks of postnatal development.

Effects of acetylcholine, isoprenaline, phenylephrine and dibutyryl-cAMP on the contractility of isolated myocytes of the rat heart ventricles

Single ventricular myocytes were isolated by enzymatic dissociation from the rat heart. The myocytes showed two types of spontaneous contractions: action potential dependent 'electric' contractions which occurred as short bursts, and slowly propagating contraction waves, i.e. phasic contractions. Electric contractions were normally found only in some of the myocytes, but in about 85% of the cells these could be induced by isoprenaline (ISO), phenylephrine (PHE), dibutyryl-cAMP (DB-cAMP) or acetylcholine (ACh). The inducing potency of the drugs was ACh greater than PHE greater than ISO greater than DB-cAMP. When electric contractions were blocked with verapamil, the frequency of phasic contractions was increased by ISO and DB-cAMP, whereas PHE and ACh had not this effect. In 45 min, ISO increased the frequency tenfold. High concentrations (10(-4) and 10(-5) M) of ISO lead to steady contracture of the myocytes in about 40% of the cells. The effect of DB-cAMP was weaker being only about 20% of that of ISO and it never caused steady contractures. The results suggest that alpha receptor activation by PHE does not affect the intracellular calcium movements but that ISO through beta receptor activation and DB-cAMP directly may increase the rate of calcium accumulation by sarcoplasmic reticulum (SR).