Table 1.

Na⁺–K⁺ ATPase, NADPH cytochrome c reductase, and InsP₃-evoked ⁴⁵Ca²⁺release in subcellular fractions of the rat brain

Subcellular fractions	Na+–K+aATPase	NADPH cytochrome c reductaseb	Basal releasec(%)	InsP3-evokedd45Ca2+ release (%)
Microsomes (P3)	2.27	1.33	2.30  ± 0.14	1.80  ± 0.18
Myelins (P2A)	2.22	0.83	1.86  ± 0.16	1.21  ± 0.15
Synaptosomes (P2B)	1.65	0.54	1.92  ± 0.11	3.61  ± 0.34
Mitochondria (P2C)	1.55	0.93	2.16  ± 0.25	1.54  ± 0.33
Synaptic vesicles (P2B1)	<0.01	0.35	2.51  ± 0.36	1.58  ± 0.33
Synaptic plasma membranes (P2B2/SPM)	1.67	0.33	2.02  ± 0.11	5.87  ± 1.24
Presynaptic mitochondria (P2B3)	0.97	0.33	1.80  ± 0.16	2.56  ± 0.44

^a,bRatios of activities of Na⁺–K⁺ ATPase (a) and NADPH cytochrome c reductase (b) in each subcellular fraction to that of starting brain homogenates. The Na⁺–K⁺ATPase activity and NADPH-cytochrome c reductase in starting homogenates were 0.112 mmol/mg of protein/min and 5.98 nmol/mg of protein/min, respectively.

^c,dResults represent basal (c) and InsP₃-evoked (d) ⁴⁵Ca²⁺release (%), represented as described in the text under Results. Data obtained with 5 μm InsP₃ (n = 3–6 separate experiments) in various subcellular preparations (300–500 μg/assay) lysed and preloaded with⁴⁵Ca²⁺.

In these experiments, preparations were divided into two groups [(P3, P2A, P2B, and P2C) and (P2B1, P2B2, and P2B3)], and experiments using each group were performed at the same time. Total⁴⁵Ca²⁺ amounts taken up into resealed vesicle preparations were 1.5–3 × 10⁴ cpm/assay for the first group and 2–4 × 10⁴ cpm/assay for the second group. Marked variations were not observed among subfractions in each group.