Intracellular ATP can regulate afferent arteriolar tone via ATP-sensitive K⁺ channels in the rabbit

Studies were performed to assess whether ATP-sensitive K⁺ (K_ATP) channels on rabbit preglomerular vessels can influence afferent arteriolar ( AA ) tone. K⁺ channels with a slope conductance of 258±13 (n = 7) pS and pronounced voltage dependence were demonstrated in excised patches from vascular smooth muscle cells of microdissected preglomerular segments. Channel activity was markedly reduced by 1 mM ATP and in a dose-dependent fashion by glibenclamide ( 10^-9 M to 10^-6 M), a specific antagonist of K_ATP channels. 10^-5 M diazoxide, a K⁺ channel opener, activated these channels in the presence of ATP, and this effect was also blocked by glibenclamide. To determine the role of these K_ATP channels in the control of vascular tone, diazoxide was tested on isolated perfused AA. After preconstriction from a control diameter of 13.1±1.1 to 3.5±2.1 μm with phenylephrine (PE), addition of 10^-5 M diazoxide dilated vessels to 11.2±0.7 μm, which was not different from control. Further addition of 10^-5 M glibenclamide reconstricted the vessels to 5.8±1.5 μm (n = 5; P < 0.03). In support of its specificity for K_ATP channels, glibenclamide did not reverse verapamil induced dilation in a separate series of experiments. To determine whether intracellular ATP levels can effect AA tone, studies were conducted to test the effect of the glycolytic inhibitor 2-deoxy-D-glucose. After preconstriction from 13.4±3.2 to 7.7±1.3 μm with PE, bath glucose was replaced with 6 mM 2-deoxy-D-glucose. Within 10 min, the arteriole dilated to a mean value of 11.8±1.4 μm (n = 6; NS compared to control). Subsequent addition of 10^-5 M glibenclamide significantly reconstricted the vessels to a diameter of 8.6±0.5 Mm (P < 0.04). These data demonstrate that K_ATP channels are present on the preglomerular vasculature and that changes in intracellular ATP can directly influence afferent arteriolar tone via these channels.