Ml. Field et al., INTRACELLULAR CA2-PERFUSED RAT-HEART - MEASUREMENT USING THE FLUORESCENT INDICATOR FURA-2( TRANSIENTS IN ISOLATED)AM/, Cell calcium, 16(2), 1994, pp. 87-100
We have investigated the nature of Fura-2/AM loading into isolated per
fused rat heart and the temporal and kinetic relationship between left
ventricular [Ca2+](i) dependent fluorescence and isovolumic pressure.
The contribution of hydrolysed mitochondrial matrix Fura-2 fluorescen
ce to that measured from the surface of the heart was estimated to be
43.9 +/- 5.5% by the addition of 100 mu M Mn2+ to the perfusate. Maxim
um endothelial Fura-2 fluorescence ratio, estimated by the addition of
3 mu M bradykinin to the perfusate, was found to constitute 33.6 +/-
2.7% of the maximum myocardial Fura-2 fluorescence ratio. Approximatel
y 11.2% of the 340 nm surface fluorescence was insensitive to 20 mM Mn
2+ in the presence of ionomycin (3 mu M) and therefore indicates the d
egree of partial hydrolysis of Fura-2/AM. Thus, depending on the contr
ibution of endothelial Fura-2 fluorescence at a physiological endothel
ial calcium concentration, cytosolic fluorescence may comprise between
11-45% of the total cellular fluorescence at 340 nm. Net tissue inter
ference of the Fura-2 fluorescence ratio by NADH emission and myoglobi
n absorption remained unaltered, providing the oxygenation state of th
e tissue was unaltered throughout the experiment. The [Ca2+](i) depend
ent fluorescence decay from peak systole was best fitted to a biexpone
ntial decay with fast and slow rate constants of 18.08 +/- 1.97 s(-1)
and 0.23 +/- 0.02 s(-1), respectively. In addition, a phase shift was
observed between temporal and kinetic measurements of the left ventric
ular isovolumic pressure and calcium dependent fluorescence traces dur
ing a contraction-relaxation cycle. We conclude that despite imperfect
Fura-2/AM loading, the temporal and kinetic characteristics of intrac
ellular [Ca2+] transients in normal isolated perfused rat heart are si
milar to those reported in more controlled preparations such as isolat
ed myocytes and cardiac trabeculae.