RESTING AND END-DIASTOLIC [CA2-PERFUSED FERRET HEART LOADED WITH A F-19 NMR INDICATOR(]I MEASUREMENTS IN THE LANGENDORFF)

Intracellular free calcium concentration ([Ca2+]i) was measured in Lan gendorff-perfused ferret hearts (30-degrees-C, pH 7.4) by loading pace d hearts with the F-19 NMR calcium indicator, the 5,5'-difluoro deriva tive of 1,2-bis(o-aminophenoxy) ethane-N, N,N',N'-tetraacetic acid (5F BAPTA), to an initial cytosolic concentration of approximately 120 muM . Increasing the pacing frequency raised the end-diastolic [Ca2+]i fro m 299 +/- 44 nM (mean +/- SEM) at 0.2 Hz to 522 +/- 54 nM at 1.0 Hz an d 691 +/- 166 nM at 2.0 Hz. Raising [Ca]o from 1.8 to 7.0 mM at a paci ng frequency of 1.0 Hz increased end-diastolic [Ca2+]i to 625 +/- 39 n M. In unpaced hearts perfused with diltiazem (100 muM), [Ca2+]i fell r apidly to a steady-state value of <1 00 nM after 60 min. Raising [Ca]o from 1.8 to 7.0 mM had no detectable effect on resting [Ca2+]i. The t ime course of the [Ca2+]i transient was measured in hearts paced at 1. 1 Hz and perfused with 1.8 mM [Ca]o. The peak [Ca2+]i was approximatel y 2 muM at approximately 150 msec after the pacing pulse, and peak dev eloped LVP occurred at 550 msec compared with 280 msec in control hear ts not loaded with 5FBAPTA. Comparisons with data obtained by other te chniques, including fluorescent [Ca2+]i indicators, imply that althoug h the end-diastolic [Ca2+]i ValUes obtained with 5FBAPTA in beating he arts are elevated by the concentrations of intracellular 5FBAPTA requi red for signal detection, the changes in [Ca2+]i observed in response to experimental interventions are qualitatively consistent with previo us data.