Responses of Cremasteric Arterioles of Spontaneously Hypertensive Rats to Changes in Extracellular K⁺ Concentration

OBJECTIVE: The goal of this study was to determine the effect of changes in extracellular K+ concentration ([K+]o) on active tone in cremasteric arterioles of spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto (WKY) and Wistar controls. METHODS: Diameters of third- and fourth-order arterioles were measured in the cremaster muscle of hypertensive and normotensive rats during abrupt changes in superfusate K+ concentration from 4.7 mM to 0 mM to 15 mM K+. RESULTS: Arterioles constricted in response to superfusion with 0 mM K+ and exhibited a large, transient dilation in response to an abrupt change from 0 mM to 15 mM [K+]o. Arteriolar dilation in response to 15 mM K+ was significantly larger in 12-15-week-old SHR than in WKY or Wistar controls. Arteriolar responses to 15 mM K+ were not significantly different in 4-6-week-old SHR and WKY. Dilator responses to 15 mM K+ were generally inhibited by 1 mM ouabain, although ouabain was less effective in inhibiting 15 mM K(+)-induced dilation in arterioles of SHR and WKY than in Wistar rats. CONCLUSIONS: Dilation of cremasteric arterioles in response to 15 mM [K+]o is mediated, at least in part, via stimulation of the electrogenic Na+/K+ pump, although Na+/K(+)-pump-independent components may also contribute to the response. Arterioles of SHR with established hypertension exhibit an altered response to elevated [K+]o which is not present in SHR in the early stage of hypertension.