1. @entity1 large-conductance voltage- and @entity460 -sensitive K+ (maxi KCa) channels are composed of at least two subunits: the pore-forming subunit, alpha, and a modulatory subunit, beta. Expression of the beta subunit induces dramatic changes in alpha subunit function. It increases the apparent @entity141 sensitivity and it allows dehydrosoyasaponin I (DHS-I) to upregulate the channel. 2. The functional coupling of maxi KCa channel alpha and beta subunits in freshly dissociated @entity1 coronary smooth muscle cells was assessed. To distinguish maxi KCa currents modulated by the beta subunit, we examined (a) their apparent @entity141 sensitivity, as judged from the voltage necessary to half-activate the channel (V1/2), and (b) their activation by DHS-I. 3. In patches with unitary currents, the majority of channels were half-activated near -85 mV at 18 microM @entity141 , a value similar to that obtained when the @entity1 KCa channel alpha (HSLO) and beta (HKV, @entity1399 ) subunits are co-expressed. A small number of channels half-activated around 0 mV, suggesting the activity of the alpha subunit alone. 4. The properties of macroscopic currents were consistent with the view that most pore-forming alpha subunits were coupled to beta subunits, since the majority of currents had values for V1/2 near to -90 mV, and currents were potentiated by DHS-I. 5. We conclude that in @entity1 coronary artery smooth muscle cells, most maxi KCa channels are composed of alpha and beta subunits. The higher @entity141 sensitivity of maxi KCa channels, resulting from their coupling to beta subunits, suggests an important role of this channel in regulating coronary tone. Their massive activation by micromolar @entity141 concentrations may lead to a large hyperpolarization causing profound changes in coronary blood flow and cardiac function.

Molecular constituents of maxi KCa channels in XXXX coronary smooth muscle: predominant alpha + beta subunit complexes.

@entity1 :: ('9606', 'Species') :: ['human', 'Human'] @entity141 :: ('CHEBI:29108', 'Chemical') :: ['Ca2+'] @entity460 :: ('MESH:D002118', 'Chemical') :: ['calcium'] @entity1399 :: ('759', 'Gene') :: ['Ca beta']
@entity1 :: (9606,Species) :: ['human']
