KATP channels and NO dilate redundantly intramuscular arterioles during electrical stimulation of the skeletal muscle in mice

Fig. 1. Skeletal muscle contraction induces an arteriolar dilation which is dependent on work intensity. Stimulation of the motor nerve in the cremaster muscle induces visible skeletal muscle contraction and arteriolar dilation. In order to enable the visibility of the arterioles under study, 0.5 s of stimulation was followed by a break lasting for 2.5 s. The dilation was substantially larger if the skeletal muscle was stimulated with a tetanic frequency (100 Hz, B) compared to a twitch frequency (10 Hz, A). The amplitude of the dilation increased with stimulation duration, and the slope of the dilation was comparable between different stimulation periods. Interestingly, the slope of the dilatory curves in response to 100 Hz stimulation was initially steeper compared to later time points. Dilations is expressed as percent of dilator capacity, n = 65 arterioles in 65 mice except for 1-s stimulation with 10 Hz (n = 45). Dashed line indicates start of stimulation at 0 s, the duration of the stimulation is given for each curve as text, and dotted lines indicate the end of stimulation (15, 30, and 60 s, respectively). Statistical comparison for different time points is given in text

Fig. 2. Blockade of adenosine receptors and inhibition of the synthesis of the endothelial autacoids NO and prostaglandins reduced active hyperemia only in combination. Arteriolar dilations during, at the end of, and after stimulation of skeletal muscle contraction at 100 Hz are depicted for the different stimulation periods. Treatments are shown in black bars; the respective control values obtained in the exact same arterioles are depicted in white bars. A Application of the non-selective adenosine receptor blocker 1,3-dipropyl-8-(p-sulfophenyl)xanthine (10 µM, DPSX, n = 7) did not change the arteriolar dilations. B The inhibition of NO synthase and cyclooxygenase (LN, Indo; 30 and 3 µM, n = 8) did also not affected active hyperemia. C A combination of these treatments (n = 24) reduced arteriolar dilations at the end of the stimulation for 15, 30, and 60 s and also during stimulation at longer stimulation periods. Dilation is given as percent of dilator capacity, *P < 0.05 vs diameter before stimulation; #P < 0.05 vs dilation of respective control; diameter values are given in Table 1. Specific time points are depicted: (1) During stimulation is the time point at 50% of total…

Fig. 3. KATP channel blockade in combination with inhibition of NO synthase and cyclooxygenase nearly abrogates active hyperemia. Arteriolar dilations during, at the end of, and after stimulation of skeletal muscle contraction at 100 Hz are depicted for the different stimulation periods (for definition of time points, see legend of Fig. 2). Treatments are shown in black bars; the respective control values obtained in the exact same arterioles are depicted in white bars. A Application of the KATP channel blocker glibenclamide (10 µM, Glib, n = 15) only moderately reduced the arteriolar dilations at longer stimulation periods. B Additional inhibition of NO synthase and cyclooxygenase (LN, Indo; 30 and 3 µM, n = 5) strongly reduced the dilations. At all time points for all stimulation periods, a significant diameter change was not observed and the dilations were attenuated compared to controls. C If only NO synthase (LN, 30 µM) was inhibited combined with Glib (n = 5), the inhibitory effect on arteriolar dilations was likewise observed except for the longest stimulation period. However, the dilation during 60-s stimulation was also significantly reduced compared to control. D In contrast,…