Table 3.

Effects of induced S68E expression on [Ca²⁺]_i transients, SR Ca²⁺ content, and myocyte contractility

	Noninduced Mice	Induced Mice
Systolic [Ca2+]i, nM
Without Iso	230 ± 22 (n = 11)	267 ± 42 (n = 10)
With Iso	557 ± 61	853 ± 95*
Diastolic [Ca2+]i, nM
Without Iso	121 ± 13	130 ± 13
With Iso	126 ± 10	137 ± 12
[Ca2+]i transient amplitude, %
Without Iso	19.8 ± 2.5	20.7 ± 4.2
With Iso	58.1 ± 4.0	73.4 ± 3.4*
t1/2 of the [Ca2+]i transient decline, ms
Without Iso	121.5 ± 12.4	135.9 ± 13.5
With Iso	64.6 ± 4.6	68.4 ± 3.5
Contraction amplitude, %
Without Iso	4.5 ± 0.7 (n = 9)	4.4 ± 0.3 (n = 10)
With Iso	14.6 ± 0.5	17.4 ± 0.9†
SR Ca2+ content, fM/fF
Without Iso	6.6 ± 0.3 (n = 5)	7.4 ± 0.4 (n = 7)
With Iso	21.6 ± 0.7 (n = 8)	27.4 ± 0.8‡ (n = 8)
t1/2 of the INaCa decline, ms
Without Iso	386 ± 59 (n = 4)	482 ± 22§ (n = 6)
With Iso	452 ± 29 (n = 8)	726 ± 123§ (n = 8)

Values are means ± SE; n, number of myocytes. Both intracellular Ca²⁺ concentration ([Ca²⁺]_i) transients (3 induced mice and 3 noninduced mice) and contraction (4 induced mice and 3 noninduced mice) were measured in myocytes incubated in 1.8 mM extracellular Ca²⁺ concentration ([Ca²⁺]_o) and stimulated to contract at 2 Hz and 37°C. Iso, when present, was at 1 μM. The [Ca²⁺]_i transient amplitude is given as the percent increase in the fura-2 signal. Contraction amplitude is given as the percent resting cell length. Sarcoplasmic reticulum (SR) Ca²⁺ content and the half-time (t_1/2) of the Na⁺/Ca²⁺ exchanger current (I_NaCa) decline after a caffeine pulse were measured at 1.8 mM [Ca²⁺]_o and 30°C (4 induced mice and 3 noninduced mice).

^*P < 0.05,

^†P < 0.03, and

^‡P < 0.0015, group (induced vs. noninduced) × Iso interaction effects;

^§P < 0.04, group effect.