Figure 1.
A, L-type calcium current (ICa(L)) versus voltage plots of sham (squares; N = 69) and postinfarction myocytes (circles; N = 60). Mean peak ICa(L) density is significantly reduced in postinfarction myocytes. *P<0.05 compared to sham (unpaired Student t-test). B, Peak ICa(L) versus cell capacitance plots of sham (squares) and postinfarction myocytes (circles). There is a linear relationship between calcium current and cell capacitance in both groups (r = -0.48, P<0.001, linear regression, for postinfarction myocytes, N = 60; r = -0.54, P<0.001, linear regression, for sham myocytes, N = 69). Slope values obtained for regression lines did not differ (-3.59 ± 0.87 for postinfarction myocytes and -5.15 ± 0.97 for sham myocytes, P = 0.24).
Figure 2.
Dose-response curves for isoproterenol on L-type calcium current (ICa(L)). Note the smaller increase of ICa(L) density in postinfarction (circles) than in sham myocytes (squares): Emax was 63.6 ± 4.3% in postinfarction and 123.3 ± 0.9% in sham myocytes, P<0.001. The EC50 was similar for both groups: 38 ± 20 nM in postinfarction and 44 ± 2 nM in sham myocytes (P>0.5, sigmoidal curve fit using logistical equation). (N), tested cell number for each point; *P<0.05 (unpaired Student t-test). Inset shows ICa(L) records in sham and postinfarction myocytes. ICa(L) was recorded in whole-cell voltage clamp mode before and during exposure to 0.1 µM isoproterenol in the same myocyte. Test voltage was 0 mV for all data.
Figure 3.
Effect of forskolin on L-type calcium current (ICa(L)). Forskolin (10 µM) added to the extracellular saline provoked similar increases in ICa(L) density in both sham (A, filled squares in the absence and filled triangles in the presence of forskolin) and postinfarction myocytes (B, open circles in the absence and open triangles in the presence of forskolin). There was no significant difference in the mean increase of ICa(L) induced by forskolin at any voltage in both groups. At -10 mV test voltage, the increases were 90.0 ± 12.9% (N = 4) in postinfarction and 91.2 ± 27.2% (N = 5) in sham myocytes (P = 0.9, unpaired Student t-test).
Figure 4.
Cytoplasmic calcium ([Ca2+]i) transient parameters obtained from isolated ventricular myocytes loaded with fura 2-AM. A, Peak amplitudes of [Ca2+]i transients measured from the resting level: 0.13 ± 0.007, N = 34, in postinfarction (MI) and 0.16 ± 0.009, N = 33, in sham myocytes (P = 0.01, unpaired Student t-test). B, Rates of increase to peak (RtPCa), and of decay to 50% amplitude (RD50) of the [Ca2+]i transients: RtPCa: 0.87 ± 0.0067, N = 34, in MI and 1.15 ± 0.075 units/s, N = 33, in sham (P<0.001) and RD50: 0.34 ± 0.028, N = 34, in MI and 0.38 ± 0.022 units/s, N = 33, in sham myocytes (P = 0.27, unpaired Student t-test). C, Peak transient amplitudes, D, RtPCa, and E, RD50 of the [Ca2+]i transients under control condition and in the presence of 1 µM isoproterenol in MI and sham myocytes. Isoproterenol induced an increase in peak amplitudes of the [Ca2+]i transients from 0.12 ± 0.02 to 0.23 ± 0.01, N = 8, in MI and from 0.16 ± 0.01 to 0.32 ± 0.04, N = 7, in sham. RtPCa was increased in MI from 0.97 ± 0.13 to 1.94 ± 0.18 units/s, N = 8, and in sham from 1.36 ± 0.40 to 3.43 ± 0.63 units/s, N = 7; isoproterenol-induced increase in RD50 was from 0.38 ± 0.07 to 0.75 ± 0.09 units/s, N = 8, in MI and from 0.45 ± 0.07 to 0.89 ± 0.13 units/s, N = 7, in sham. Measurements of [Ca2+]i transients were always performed first under control condition and then in the presence of the drug in the same cell. Each cell was exposed only once to isoproterenol to avoid desensitization. F, Sample records from one MI and one sham cell, bathed in control saline (control) and at 3rd minute of exposure to 1 µM isoproterenol. *P<0.05 for comparisons between MI and sham, and +P<0.05 for comparisons between isoproterenol and control (unpaired Student t-test). Iso, isoproterenol.
Figure 5.
Saturation binding isotherm of [3H]-DHA binding to left ventricle homogenates in sham (squares) and myocardial infarction (MI) rat heart (circles). Inset shows Scatchard analysis of the data. Bmax was 93.89 ± 20.22 in MI and 271.5 ± 31.43 fmol/mg protein in sham, P = 0.009, nonlinear regression according to rectangular hyperbolic model, N = 3. No significant difference in Kd values was observed between the groups: 10.69 ± 3.78 for MI and 11.37 ± 3.68 nM for sham hearts. The average values were obtained in three duplicate experiments.
