Potassium initiates vasodilatation induced by a single skeletal muscle contraction in hamster cremaster muscle

Abstract

The rapid onset of vasodilatation within seconds of a single contraction suggests that the vasodilators involved may be products of skeletal muscle activation, such as potassium (K(+)). To test the hypothesis that K(+) was in part responsible for the rapid dilatation produced by muscle contraction we stimulated four to five skeletal muscle fibres in the anaesthetized hamster cremaster preparation in situ and measured the change in diameter of arterioles at a site of overlap with the stimulated muscle fibres before and after a single contraction stimulated over a range of stimulus frequencies (4, 10, 20, 30, 40, 60 and 80 Hz; 250 ms train duration). Muscle fibres were stimulated in the absence and presence of an inhibitor of a source of K(+), the voltage dependent K(+) channel inhibitor 3,4-diaminopyridine (DAP, 3 x 10(-4) M) and inhibitors of the K(+) dilatory signal transduction pathway, either a Na(+) K(+)-ATPase inhibitor (ouabain; 10(-4) M) or an inward rectifying K(+) channel inhibitor (barium chloride, BaCl(2); 5 x 10(-5) M). We observed significant inhibitions of the rapid dilatation at all stimulus frequencies with each inhibitor. The dilatory event at 4 s was significantly inhibited at all stimulus frequencies by an average of 65.7 +/- 3.6%, 58.8 +/- 6.1% and 64.4 +/- 2.1% in the presence DAP, ouabain and BaCl(2), respectively. These levels of inhibition did not correlate with non-specific changes in force generation by skeletal muscle measured in vitro. Therefore, our data support that K(+) is involved in the rapid dilatation in response to a single muscle contraction across a wide range of stimulus frequencies.

Figure 1. The change in diameter over time in response to a single contraction at 4 Hz (A) 20 Hz (B) and 60 Hz (C)

Representative data (control data from the BaCl₂ experiment) showing the three typical patterns of dilatation observed over a range of stimulus frequencies. *Data or the range of data significantly different from 0.

Figure 2. The effect of 3 × 10⁻⁴m DAP on the change in diameter at 4 s (A) and 20 s (B) across all stimulus frequencies tested

*Control change in diameter significantly different from diameter in the presence of DAP. At 4 s the P values for main and interactive effects were: drug < 0.0001, frequency < 0.0001, and drug–frequency interaction = 0.13, and at 20 s these were 0.0077, < 0.0001 and 0.53, respectively.

Figure 3. The effect of 10⁻⁴m ouabain on the change in diameter at 4 s (A) and 20 s (B) across all stimulus frequencies tested

*Control change in diameter is significantly different from diameter in the presence of ouabain. At 4 s the P values for main and interactive effects were: drug < 0.0001, frequency < 0.0001, and drug–frequency interaction = 0.58, and at 20 s these were < 0.0001, < 0.0001, and 0.41, respectively.

Figure 4. The effect of 5 × 10⁻⁵m BaCl₂ (□) and 10⁻⁸m PHE (▪) on the change in diameter at 4 s (A) and 20 s (B) across all stimulus frequencies tested

The change in diameter is represented by the change in diameter under control conditions minus the change in diameter under experimental conditions (Control–Expt.). *Control change in diameter significantly different from diameter in the presence of BaCl₂. At 4 s the P values for main and interactive effects were: drug < 0.0001, frequency = 0.0095, and drug–frequency interaction = 0.58, and at 20 s these were 0.0044, 0.0045, 0.86, respectively.

Figure 5. Time controls for the data in Figs 2–4

Skeletal muscle cells were stimulated over a range of stimulus frequencies (first stimulation series, ▪) and then again following 30 min (second stimulation series, □). A, effect of stimulating the preparation twice with no treatment on the change in diameter at 4 s. B, effect of stimulating the preparation twice with no treatment on the change in diameter at 20 s. At 4 s the P values for main and interactive effects were: time = 0.6143, frequency = < 0.0001 and time–frequency interaction = 0.6410, and at 20 s these were 0.6143, < 0.0001, and 0.8720, respectively.