Functional evidence of a role for two-pore domain potassium channels in rat mesenteric and pulmonary arteries

1 Experiments were performed to elucidate the mechanism by which alterations of extracellular pH (pH(o)) change membrane potential (E-M) in rat mesenteric and pulmonary arteries. 2 Changing pH(o) from 7.4 to 6.4 or 8.4 produced a depolarisation or hyperpolarisation, respectively, in mesenteric and pulmonary arteries. Anandamide (10 muM) or bupivacaine (100 muM) reversed the hyperpolarisation associated with alkaline pH(o), shifting the E-M of both vessels to levels comparable to that at pH 6.4. In pulmonary arteries, clofilium (100 muM) caused a significant reversal of hyperpolarisation seen at pH 8.4 but was without effect at pH 7.4. 3 K+ channel blockade by 4-aminopyridine (4-AP) (5 mM), tetraethylammonium (TEA) (10 mM), Ba2+ (30 muM) and glibenclamide (10 muM) depolarised the pulmonary artery. However, shifts in E-M with changes in pH(o) remained and were sensitive to anandamide (10 muM), bupivacaine (100 muM) or Z(2+) (200 muM). 4 Anandamide (0.3-60 muM) or bupivacaine (0.3-300 muM) caused aconcentration-dependent increase in basal tone in pulmonary arteries. 5 RT-PCR demonstrated the expression of TASK-1, TASK-2, THIK-1, TRAAK, TREK-1, TWIK-1 and TWIK-2 in mesenteric arteries and TASK-1, TASK-2, THIK-1, TREK-2 and TWIK-2 in pulmonary arteries. TASK-1, TASK-2, TREK-I and TWIK-2 protein was demonstrated in both arteries by immunostaining. 6 These experiments provide evidence for the presence of two-pore domain K+ channels in rat mesenteric and pulmonary arteries. Collectively, they strongly suggest that modulation of TASK-1 channels is most likely to have mediated the pH-induced changes in membrane potential observed in these vessels, and that blockade of these channels by anandamide or bupivacaine generates a small increase in pulmonary artery tone.