Tri-iodothyronine increases intra-cellular calcium levels in single rat myocytes.
We have studied the effects of acute administration of triiodothyronine (T3) on cytosolic free calcium levels [Ca2+]i in single rat myocytes microinjected with aequorin. Ventricular myocytes were isolated by perfusing rat hearts with collagenase, and healthy, rod-shaped cells were injected to less than 1% of their volume with aequorin. The photons emitted from single cells were measured and a conversion to [Ca2+]i made on the basis of an in vitro calibration after the remaining aequorin had been discharged by cell lysis. Only cells that depolarized reversibly (showing elevated [Ca2+]i levels) when superfused with 80 mM KCl, and which gave a substantial signal on lysis with distilled water were used. The [Ca2+]i rose from a resting value of 150 +/- 56 nM (mean +/- SD, n = 14) by 127 +/- 47 nM on depolarization with 80 mM KCl. Application of T3 (1-100 nM) led to an increase (P less than 0.05) in [Ca2+]i (mean amplitude of 152 +/- 35 nM) before returning to baseline. The median duration of these events was 10 min (range = 1.4-34.4 min). The time to response was shorter when 100 nM T3 was applied (median and range; 6.8, 0-14 min) than when 1 nM T3 was used (16, 7.0-56.1 min) (P less than 0.05). To conclude, physiological concentrations of thyroid hormones caused rapid but transient stimulation of [Ca2+]i in single rat myocytes.
Lomax
R B
RB
Department of Medicine (Clinical Biochemistry), University of Manchester, Hope Hospital, Salford.
Cobbold
P H
PH
Allshire
A P
AP
Cuthbertson
K S
KS
Robertson
W R
WR
D000331:Aequorin / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D008297:Male; D003012:Microbial Collagenase / Q000737:chemistry; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014284:Triiodothyronine / Q000008:administration & dosage / Q000494:pharmacology*
D014284:Triiodothyronine; D000331:Aequorin; D003012:Microbial Collagenase; D002118:Calcium