Figure 3. Effects of ouabain concentration on myogenic tone in WT arteries; roles of the Na⁺ pump α1 and α2 isoforms.

Aa, fluo-4 pseudocolor images from a representative artery captured at the times (i–iii) indicated in graph b. Ab, simultaneous [Ca²⁺]_cyt and diameter changes during exposure to 10 nm ouabain in an artery (Aa) with myogenic tone (n = 6). Scale bar, 10 μm. B, effect of 10 nm ouabain on myogenic tone in a representative artery in the absence of fluo-4. Ouabain (10 nm) increased myogenic tone (MT) from 21 ± 2% to 25 ± 2% of passive diameter (PD) (n = 7; P < 0.01). C, effect of 10 μm ouabain on myogenic tone in a representative artery in the absence of fluo-4. Ouabain (10 μm) increased myogenic tone (MT) from 23 ± 3% to 33 ± 4% of passive diameter (PD) (n = 5; P < 0.01). D, change in myogenic tone (ΔMT, as a percentage of control MT) graphed as a function of ouabain concentration (n = 7). Brackets at the right indicate the components of ΔMT that correspond to inhibition of the Na⁺ pump high ouabain affinity α2 and low ouabain affinity α1 isoforms, respectively. *P < 0.05; **P < 0.01 versus control (before ouabain); the value at 10 μm was significantly greater than at 100 nm or 1 μm (P < 0.01). E, immunoblots of Na⁺ pump α subunit isoform (α1, α2 and α3) distribution in mouse mesenteric artery and other tissues. Numbers are micrograms of protein per lane. Since the skeletal muscle (SkM) α1:α2 ratio is ≈1:4 (He et al. 2001; Golovina et al. 2003), the normalized band densities (see Methods) indicate that mesenteric artery α1:α2 ≈ 4:1 and heart α1:α2 ≈ 6.3:1.