Functional and Molecular Evidence for Impairment of Calcium-Activated Potassium Channels in Type-1 Diabetic Cerebral Artery Smooth Muscle Cells

Abstract

Cerebral vascular dysfunction and associated diseases often occur in type-1 diabetes, but the underlying mechanisms are largely unknown. In this study, we sought to determine whether big-conductance, Ca(2+)-activated K(+) (BK) channels were impaired in vascular (cerebral artery) smooth muscle cells (CASMCs) from streptozotocin-induced type-1 diabetic mice using patch clamp, molecular biologic, and genetic approaches. Our data indicate that the frequency and amplitude of spontaneous transient outward currents (STOCs) are significantly decreased, whereas the activity of spontaneous Ca(2+) sparks is increased, in diabetic CASMCs. The sensitivity of BK channels to voltage, Ca(2+), and the specific inhibitor iberiotoxin are all reduced in diabetic myocytes. Diabetic mice show increased myogenic tone and decreased contraction in response to iberiotoxin in cerebral arteries and elevated blood pressure. The expression of the BK channel beta1, but not alpha-subunit protein, is markedly decreased in diabetic cerebral arteries. Diabetic impairment of BK channel activity is lost in CASMCs from BK channel beta1-subunit gene deletion mice. In conclusion, the BK channel beta1-subunit is impaired in type-1 diabetic vascular SMCs, resulting in increased vasoconstriction and elevated blood pressure, thereby contributing to vascular diseases in type-1 diabetes.

Reduced Ca2+ Spark Activity after Subarachnoid Hemorrhage Disables BK Channel Control of Cerebral Artery Tone

“…Although altered frequency of Ca 2+ spark-induced transient BK currents has been reported in other cardiovascular diseases such as hypertension and hypovolemic shock, these phenomena have been attributed to altered BK channel function/expression. Enhanced constriction associated with hypertension and diabetes has been linked to decreased expression of the BK channel b 1 -subunit (Amberg and Santana, 2003;Brenner et al, 2000;Dong et al, 2008), whereas an acute upregulation of BK channel b 1 -subunit contributes to vasodilation and the decrease in peripheral resistance associated with hemorrhagic shock (Zhao et al, 2007). In the above-mentioned pathologies, Ca 2+ spark activity was unaltered.…”

“…Loss-of-and gain-of-function polymorphisms of KCNMA1 and KCNMB1 have been linked to asthma and blood pressure regulation in humans (Kelley-Hedgepeth et al, 2009;Tomas et al, 2008). Furthermore, decreased KCNMB1 expression causes reduced BK channel Ca 2+ and voltage sensitivity, and is linked to enhanced vasoconstriction, hypertension, and diabetes (Amberg and Santana, 2003;Brenner et al, 2000;Dong et al, 2008). These vascular pathologies have all been associated with a decrease in BK channel activity in response to Ca 2+ sparks, rather than with a reduction in Ca 2+ spark activity.…”

The Vascular Conducted Response in Cerebral Blood Flow Regulation

“…In hypertensive animals, cerebral artery BK Ca channels are upregulated, 65 whereas in diabetic mice and rats the b 1 -subunit of the BK Ca channel is downregulated, leading to impaired function of the channel. 66,67 Thus, it can be expected that the changes in BK Ca channel expression and function modifies the length constant of VCRs in these diseases. Having defined a key role of K þ channels for modulation of VCRs, it can be predicted that intracellular regulators of K þ channel activity, such as PKC, PKA, 20-HETE, epoxyeicosatrienoic acid (EETs), prostaglandins, and PIP 2 would be capable of regulating VCRs.…”

Functional Role of Canonical Transient Receptor Potential 1 and Canonical Transient Receptor Potential 3 in Normal and Asthmatic Airway Smooth Muscle Cells

“…The holding potential was routinely set at 250 mV. Currents were analyzed offline using Clampfit-9 software (Axon Instruments, Union City, CA) at 1 kHz and the 50% amplitude threshold method with excluding any events lasting for less than 0.664 ms (2 3 rise time), as reported previously (8,17). The open probability (NPo) was calculated using the equation: NPo 5 total open time of all channel levels in the patch/sample recording.…”

“…Single NSCC currents were recorded with an EPC-10 patch-clamp system (Heka Electronics, Lambrecht, Germany) at 10 kHz using the inside-out recording configuration of the patch clamp technique (8,17) at room temperature (z 228C). Patch pipettes had resistances of approximately 8 MV when filled with patch pipette solution.…”