Regulation of capillary hemodynamics by K

ATP‐sensitive K+ channels (KATP) have been implicated in the regulation of resting vascular smooth muscle membrane potential and tone. However, whether KATP channels modulate skeletal muscle microvascular hemodynamics at the capillary level (the primary site for blood‐myocyte O2 exchange) remains unknown. We tested the hypothesis that KATP channel inhibition would reduce the proportion of capillaries supporting continuous red blood cell (RBC) flow and impair RBC hemodynamics and distribution in perfused capillaries within resting skeletal muscle. RBC flux (f RBC), velocity (V RBC), and capillary tube hematocrit (Hctcap) were assessed via intravital microscopy of the rat spinotrapezius muscle (n = 6) under control (CON) and glibenclamide (GLI; KATP channel antagonist; 10 µM) superfusion conditions. There were no differences in mean arterial pressure (CON:120 ± 5, GLI:124 ± 5 mmHg; p > 0.05) or heart rate (CON:322 ± 32, GLI:337 ± 33 beats/min; p > 0.05) between conditions. The %RBC‐flowing capillaries were not altered between conditions (CON:87 ± 2, GLI:85 ± 1%; p > 0.05). In RBC‐perfused capillaries, GLI reduced f RBC (CON:20.1 ± 1.8, GLI:14.6 ± 1.3 cells/s; p 0.05). The absence of GLI effects on the %RBC‐flowing capillaries and Hctcap indicates preserved muscle O2 diffusing capacity (DO2m). In contrast, GLI lowered both f RBC and V RBC thus impairing perfusive microvascular O2 transport (Q̇m) and lengthening RBC capillary transit times, respectively. Given the interdependence between diffusive and perfusive O2 conductances (i.e., %O2 extraction∝DO2m/Q̇m), such GLI alterations are expected to elevate muscle %O2 extraction to sustain a given metabolic rate. These results support that KATP channels regulate capillary hemodynamics and, therefore, microvascular gas exchange in resting skeletal muscle.
Superfusion of the rat spinotrapezius muscle with the sulfonylurea glibenclamide (GLI) was used to locally inhibit KATP channels in vivo. GLI reduced both red blood cell (RBC) flux and velocity thereby impairing perfusive microvascular O2 transport and lengthening RBC capillary transit times, respectively. These results support that KATP channels regulate capillary hemodynamics and microvascular gas exchange in resting skeletal muscle.