Cardiac microvascular and aortic endothelial cells express different types of voltage-gated K⁺ currents

Significant functional differences have been documented between macrovascular and microvascular endothelial cells. However, except for ultrastructural features, few differential markers have ever been reported between the two cell types. Since voltage-gated K⁺ channels represent a large and diverse family of integral membrane proteins we studied the properties of these channels in macrovascular and microvascular endothelial cells using the whole-cell arrangement of the patch clamp technique. Rat cardiac microvascular endothelial cells (CMECs) were isolated through a series of procedures consisting of ventricular dissection, tissue enzyme digestion, and differential attachment Aortic endothelial cells (AECs) were obtained by expiant of aortic rings into matrigel-coated dishes. Voltage steps positive to -30 mV resulted in the activation of a time-dependent, delayed rectifier K⁺ current (I_K) in the CMECs I_K was completely blocked during external application of charybdotoxin (CTX) (50 nM) and TEA (100 mM). In contrast, the AECs expressed a transient outward K⁺ current that decayed with a time constant of 37 ± 5 ms and was insensitive to CTX and TEA. Thus, voltage-gated K⁺ channels expressed in macrovascular and microvascular cells have different biophysical and pharmacological properties.