TY - JOUR
T1 - Effects of verapamil, dibutyryl cyclic AMP, and extracellular calcium on intracellular free calcium concentrations in myocytes isolated from rat ventricles
AU - Auld, Amanda M.
AU - Aspinall, James
AU - Barritt, Gregory J.
PY - 1987/10
Y1 - 1987/10
N2 - Summary: The concentration of free calcium in the myoplasm of myocytes isolated from rat ventricles was measured using quin2. Incubation of myocytes with the acetoxymethylester of quin2 (50 μmol·litre-1) for 45 min was required to give effective loading with quin2. At 1 mmol·litre-1extracellular calcium free calcium was 210(17) (n = 5) nmol·litre-1. Depolarisation of myocytes by addition of 40 mmol·litre-1 potassium caused a threefold increase in free calcium. Increases in extracellular calcium from 0.25 to 2.0 mmol·litre-1 caused a twofold increase in free calcium in polarised (resting) myocytes and a 2.5-fold increase in cells depolarised with potassium. The ability of verapamil to inhibit the electrically stimulated contraction of myocytes was dependent on the stimulation voltage. Half-maximal inhibition was given by 0.7 and 2 μmol·litre-1 verapamil at 50 and 100 V stimulation respectively. High concentrations of verapamil completely inhibited potassium induced increases in the fluorescence of quin2 loaded cells. Half-maximal inhibition was observed at 0.5 μmol·litre-1 verapamil. The calcium agonist CGP 28392 enhanced potassium induced fluorescence of quin2 loaded cells. Dibutyryl cyclic adenosine monophosphate and adrenaline increased the proportion of rod shaped cells that contracted in response to stimulation by low, but not high, voltage. Dibutyryl cyclic AMP caused a threefold increase in the potassium induced increase in free calcium. It is concluded that verapamil decreases and that calcium agonists, dibutyryl cyclic AMP, and increases in extracellular calcium increase free calcium, as monitored by intracellular quin2.
AB - Summary: The concentration of free calcium in the myoplasm of myocytes isolated from rat ventricles was measured using quin2. Incubation of myocytes with the acetoxymethylester of quin2 (50 μmol·litre-1) for 45 min was required to give effective loading with quin2. At 1 mmol·litre-1extracellular calcium free calcium was 210(17) (n = 5) nmol·litre-1. Depolarisation of myocytes by addition of 40 mmol·litre-1 potassium caused a threefold increase in free calcium. Increases in extracellular calcium from 0.25 to 2.0 mmol·litre-1 caused a twofold increase in free calcium in polarised (resting) myocytes and a 2.5-fold increase in cells depolarised with potassium. The ability of verapamil to inhibit the electrically stimulated contraction of myocytes was dependent on the stimulation voltage. Half-maximal inhibition was given by 0.7 and 2 μmol·litre-1 verapamil at 50 and 100 V stimulation respectively. High concentrations of verapamil completely inhibited potassium induced increases in the fluorescence of quin2 loaded cells. Half-maximal inhibition was observed at 0.5 μmol·litre-1 verapamil. The calcium agonist CGP 28392 enhanced potassium induced fluorescence of quin2 loaded cells. Dibutyryl cyclic adenosine monophosphate and adrenaline increased the proportion of rod shaped cells that contracted in response to stimulation by low, but not high, voltage. Dibutyryl cyclic AMP caused a threefold increase in the potassium induced increase in free calcium. It is concluded that verapamil decreases and that calcium agonists, dibutyryl cyclic AMP, and increases in extracellular calcium increase free calcium, as monitored by intracellular quin2.
KW - Calcium physiology
KW - Dibutyryl cyclic AMP
KW - Heart physiology
KW - Isolated cardiac myocytes
KW - Myoplasmic free calcium concentration
KW - Verapamil
UR - http://www.scopus.com/inward/record.url?scp=85047675581&partnerID=8YFLogxK
U2 - 10.1093/cvr/21.10.772
DO - 10.1093/cvr/21.10.772
M3 - Review article
C2 - 2830972
AN - SCOPUS:85047675581
VL - 21
SP - 772
EP - 778
JO - Cardiovascular Research
JF - Cardiovascular Research
SN - 0008-6363
IS - 10
ER -