Preserved regulation of renal perfusion pressure by small and intermediate conductance K^sub Ca^ channels in hypertensive mice with or without renal failure

The purpose of this study was to assess, in the murine kidney, the mechanisms underlying the endothelium-dependent control of vascular tone and whether or not, in a severe model of hypertension and renal failure, K^sub Ca^ channels contribute to its regulation. Wild-type (BL) and double-transgenic female mice expressing human angiotensinogen and renin (AR) genes received either control or a high-salt diet associated to a nitric oxide (NO) synthase inhibitor treatment (BLSL and ARSL). Changes in renal perfusion pressure (RPP) were measured in isolated perfused kidneys. BLSL and AR were moderately hypertensive without kidney disease while ARSL developed severe hypertension and renal failure. In the four groups, methacholine induced biphasic endothelium-dependent responses, a transient decrease in RPP followed by a cyclooxygenase-dependent increase in RPP. In the presence or not of indomethacin, the vasodilatations were poorly sensitive to NO synthase inhibition. However, in the presence of cyclooxygenase and NO synthase inhibitors, apamin, and/or TRAM-34, blockers of K^sub Ca^2.3 and K^sub Ca^3.1, respectively, abolished the decrease in RPP in response to either methacholine or the two activators of K^sub Ca^2.3/K^sub Ca^3.1, NS309, and SKA-31. Thus, K^sub Ca^2/3 channels play a major role in the regulation of murine kidney perfusion and this mechanism is maintained in hypertension, even when severe and associated with kidney damage.