Expression of Shaker‐Type Voltage‐gated K + Channels in Human Conduit and Resistance Arteries

The expression and function of voltage‐gated potassium (K V ) channels have been characterized in different vascular beds from a variety of animal species. Our recent studies indicate that 4‐aminopyridine (4‐AP)‐sensitive K V channels (especially shaker‐type K V 1 family) mediate vasodilator responses to hydrogen peroxide (H 2 O 2 ) in human coronary and adipose arterioles; however, the molecular identity of these K V channels remains unclear. The goal of this study was to identify α‐ (pore‐forming) and β‐ (accessory) subunit composition of K V 1 channels using molecular, immunological, and patch‐clamp techniques. Human conduit (>500 μm) and resistance (100–200 μm) arteries were freshly isolated from heart and adipose (subcutaneous and visceral) tissues obtained from unused donor hearts or discarded surgical specimens (n=12 and 15 for heart and adipose tissues, respectively). We first examined mRNA transcripts of K V 1α and β subunits using RT‐PCR. Of 9 subunits examined in coronary and adipose vascular tissues, four subunits were consistently detected including K V α1.5 and K V β1.1–1.3. Other K V 1 subunits (K V α1.1–1.4 and α1.6) were variably detected in some but not other tissues. As a positive control, the human brain tissue was found to express mRNAs of all the K V 1 subunits. Consistent with mRNA expression profile, K V α1.5 and β1.2 proteins were detected in both coronary and adipose vessels using Western blot. These same tissue samples also revealed protein expression of K V α1.3–1.4 and α1.6. Immunofluorescence assay of freshly dissociated vascular cells revealed that K V α1.5 proteins are abundantly expressed in vascular smooth muscle cells (VSMCs) whereas K V α1.4 and α1.6 seem to be mainly localized in endothelial cells (ECs). Finally, whole‐cell K + currents recorded from coronary and adipose VSMCs were markedly reduced by 4‐AP (5 mM; general K V blocker) and DPO‐1 (1 μM; K V 1.5 blocker). In conclusion, the expression of K V 1 channels is highly cell‐specific in human coronary and adipose vessels, with predominant localization of K V α1.5 in VSMCs but different K V 1 channels (e.g., K V α1.4 and α1.6) in ECs. How these specific K V 1 channels mediate vasodilator responses to H 2 O 2 or other vasoactive agents remains to be determined.