Arteriolar myogenic vasoconstriction occurs when increased stretch or membrane tension leads to smooth muscle cell (SMC) depolarization and opening of voltage-gated Ca²⁺ channels. To prevent a positive feedback situation leading to excessive pressure-induced vasoconstriction, studies in cerebral artery smooth muscle have suggested that activation of the large conductance, Ca²⁺-activated, K⁺ channel (BK_Ca) provides an opposing hyperpolarizing influence to reduce Ca²⁺ channel activity. We have hypothesized that this mechanism may not, however, equally apply to all vascular beds. In particular, it is unlikely that BK_Ca plays a major role in arterioles of resting skeletal muscle where there is typically a high resistance to tissue blood flow. To establish the existence of such heterogeneity in vascular reactivity, studies were performed on cells dispersed from cremaster muscle arterioles and small cerebral arteries of rats. Whole cell K⁺ currents were determined at pipette [Ca²⁺] of 100 nM or 5 μM in the presence and absence of the specific BK_Ca inhibitor, iberiotoxin (IBTX; 0.1 μM). Similar total outward current densities were observed for the two cell preparations at the lower pipette Ca²⁺ levels. At 5 μM Ca²⁺, however, cremaster VSM showed a significantly (p < 0.05) lower current density compared to cerebral VSM (34.5 ± 1.9 vs 45.5 ± 1.7 pA pF-1 at +70mV). Studies with IBTX suggested that differences in K⁺ conductance between cremaster and cerebral cells at 5 μM intracellular [Ca²⁺] were largely due to activity of BK_Ca. 17β-Estradiol (E2), reported to potentiate BKCa current via the channel’s β-subunit, caused a significantly greater effect on whole cell K⁺ currents in cerebral vessel SMCs compared to those of cremaster muscle. In contrast, the alpha subunit-selective BK_Ca opener, NS-1619, exerted a similar effect in cremaster and cerebral cells. Spontaneously transient outward currents (STOCs) were more apparent (in terms of frequency and amplitude) and occurred at more negative membrane potentials in cerebral SMCs, compared to cremaster SMCs. Also consistent with decreased STOC activity in the cremaster SMCs was an absence of detectable Ca²⁺ sparks (0 out of 76 cells) compared to that in cerebral SMCs (76 out of 105 cells). Measurements based upon mRNA and protein detection indicated a higher ratio of BK_Ca β:α-subunit expression in cerebral vessel SMCs compared to that from cremaster muscle. The data thus support vascular heterogeneity with respect to the activity of BK_Ca. Specifically, in cremaster arteriole SMCs, BK_Ca appears to show a relative decrease in β-subunit regulation of the channel compared to that in cerebral SMCs. We hypothesize that this reduced BKCa activity contributes to the increased vascular tone and resistance observed in cremaster arterioles versus comparable arteries from the cerebral circulation.