Contribution of electromechanical coupling between KV and CaV1.2 channels to coronary dysfunction in obesity

Previous investigations indicate that diminished functional expression of voltage-dependent K ? (KV) channels impairs control of coronary blood flow in obesity/ metabolic syndrome. The goal of this investigation was to test the hypothesis that KV channels are electromechanically coupled to Ca(V)1.2 channels and that coronary microvascular dysfunction in obesity is related to subsequent increases in Ca(V)1.2 channel activity. Initial studies revealed that inhibition of KV channels with 4-aminopyridine (4AP, 0.3 mM) increased intracellular [Ca2+], contracted isolated coronary arterioles and decreased coronary reactive hyperemia. These effects were reversed by blockade of Ca(V)1.2 channels. Further studies in chronically instrumented Ossabaw swine showed that inhibition of Ca(V)1.2 channels with nifedipine (10 lg/kg, iv) had no effect on coronary blood flow at rest or during exercise in lean swine. However, inhibition of Ca(V)1.2 channels significantly increased coronary blood flow, conductance, and the balance between coronary flow and metabolism in obese swine (P < 0.05). These changes were associated with a similar to 50 % increase in inward Ca(V)1.2 current and elevations in expression of the pore-forming subunit (a1c) of Ca(V)1.2 channels in coronary smooth muscle cells from obese swine. Taken together, these findings indicate that electromechanical coupling between KV and Ca(V)1.2 channels is involved in the regulation of coronary vasomotor tone and that increases in Ca(V)1.2 channel activity contribute to coronary microvascular dysfunction in the setting of obesity.