Functional and molecular characterization of maxi K+-channels (BKCa) in buffalo myometrium

Large conductance potassium channels (BKCa channels) play a central role in maintaining myometrial tone, thus activation of these channels proved to have therapeutic potential in preterm labor. Present study aims to unravel the presence of BKCa (maxi-K) channels in buffalo myometrium. Tension experiments, mRNA and protein expression studies were done to characterize BKCa channels in buffalo myometrium. Isolated myometrial preparations exhibited rhythmic spontaneity with regular pattern of amplitude and frequency. Selective blockers of BKCa channels iberiotoxin (IbTx; 100 nM) and tetraethylammonium (TEA; 1 mM) produced excitatory effects as evidenced by increase in amplitude and frequency of myogenic activity. 1,3-Dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimi-dazol-2-one (NS-1619; 10−7–10−4 M), a BKCa channel opener, produced concentration-dependent relaxation of myometrium with pD2 of 5.02 ± 0.19 and Rmax of 31.35 ± 3.5% (n = 5). TEA significantly antagonized NS-1619-induced relaxation (pD2 of 4.72 ± 0.12 and Rmax of 22.72 ± 1.78%; n = 5). IbTx also significantly shifted the dose response curve of NS-1619 towards right (pD2 of 3.98 ± 0.16; n = 4) without significant change in the per cent maximal response. Further, RT-PCR study detected mRNA encoding BKCa α-subunit and Western blot analysis detected its protein expression in myometrium. Based on the results of the present investigation, it is suggested that BKCa channels are present in the buffalo myometrium and are open in the resting state. Thus, their activation by potassium channel opener/β2-adrenoceptor agonist (tocolytic drug) may lead to uterine relaxation in preterm labor.