Potassium (BK_Ca) currents are reduced in microvascular smooth muscle cells from insulin-resistant rats

Abstract

Insulin resistance (IR) syndrome is associated with impaired vascular relaxation; however, the underlying pathophysiology is unknown. Potassium channel activation causes vascular smooth muscle hyperpolarization and relaxation. The present study determined whether a reduction in large conductance calcium- and voltage-activated potassium (BK(Ca)) channel activity contributes to impaired vascular relaxation in IR rats. BK(Ca) channels were characterized in mesenteric microvessels from IR and control rats. Macroscopic current density was reduced in myocytes from IR animals compared with controls. In addition, inhibition of BK(Ca) channels with tetraethylammonium (1 mM) or iberiotoxin (100 nM) was greater in myocytes from control (70%) compared with IR animals (approximately 20%). Furthermore, activation of BK(Ca) channels with NS-1619 was three times more effective at increasing outward current in cells from control versus IR animals. Single channel and Western blot analysis of BK(Ca) channels revealed similar conductance, amplitude, voltage sensitivity, Ca2+ sensitivity, and expression density between the two groups. These data provide the first direct evidence that microvascular potassium currents are reduced in IR and suggest a molecular mechanism that could account for impaired vascular relaxation in IR.

Cerebrovascular Dysfunction in Zucker Obese Rats Is Mediated by Oxidative Stress and Protein Kinase C

“…Using immunoblot analysis we found that levels of the BK Ca ␣, Kir6.1-6.2, and Kir2.1 proteins (the pore-forming subunits of the BK Ca , K ATP , and K ir -channels, respectively) are not detectably affected by IR. These findings are consistent with the results of a previous study (46) in which the expression of the BK Ca ␣ subunit in mesenteric arteries was found to be unaffected by IR, although the same channel subunit has been found to be upregulated in other vascular disease states (33).…”

cAMP activates BKCachannels in pulmonary arterial smooth muscle via cGMP-dependent protein kinase

“…Single-channel currentvoltage relationships yielded an average single-channel conductance of 142 Ϯ 5 pS (n ϭ 3; Fig. 2B), which agrees with other studies reporting BK Ca channel conductance in vascular smooth muscle (6,11). Furthermore, raising Ca 2ϩ concentration at the cytoplasmic face of the patch membrane increased channel gating dramatically (Figs.…”

“…Whole cell currents were measured from metabolically intact PASMC using the amphotericinperforated-patch technique (6,11). In contrast to standard whole cell techniques, perforated-patch recordings provide accurate current measurement with only minimal current decay or loss of soluble cytoplasmic components due to cellular dialysis.…”

“…Currents were filtered at 2 kHz and digitized at 10 kHz. Channel activity was quantified by calculating the single, open-channel probability (NPo) as described previously (11,42).…”

Protein kinase C inhibits BKCachannel activity in pulmonary arterial smooth muscle

“…All drugs were diluted into fresh bath solution (1 ml) and perfused into a 2-ml recording chamber (Warner Instruments). Channel activity was quantified by calculating the single channel open probability (NP o) over the duration of the entire data file, as described previously (10,12,39,40).…”