Different expression of large-conductance calcium-activated K+ channels in human internal mammary and radial arteries

Aims In this study, we investigated and compared the electrophysiological and molecular properties of large-conductance Ca2+-activated K+ (BKCa) channels between human internal mammary arteries (IMA) and radial arteries (RA). Methods and results IMA and RA sections were obtained from 79 patients (including 9 females) undergoing coronary artery bypass graft surgery. We examined the effects of K+ channel blockers tetraethylammonium (TEA), iberiotoxin (IBTX), and 4-aminopyridine (4-AP) on isolated smooth muscle cells (SMCs) using patch clamping. Both TEA (1 mM) and IBTX (0.1 mu M) significantly decreased K+ currents in IMA SMCs and RA SMCs, while 4-AP (1 mM) only had a weak effect. IBTX had a greater K+-blocking effect on IMA SMCs than on RA SMCs. Consistently, TEA and IBTX evoked significant constriction of both intact vascular rings. IBTX had a greater constrictor effect on IMA rings (18.5 +/- 6.7%, n = 8) than on RA rings (10.6 +/- 3.1%, n = 8), P < 0.05. RT-PCR and western blot analysis demonstrated that gene and protein expression of the alpha-subunit of BKCa channels from IMA was greater than that from RA. Conclusion The density of BKCa channels is greater in human IMA than in RA resulting in greater BKCa currents in SMCs from IMA. This may partly explain the finding of less spasm in IMA grafts than in RA grafts. Our results may be of value in determining the best anti-spasm agent to use peri-operatively.