Phosphorylation modulates the activity of the ATP-sensitive K⁺ channel in the ventromedial hypothalamic nucleus

Regulation of the ATP-sensitive K⁺ (K-ATP) channel was examined in cell-attached and inside-out membrane patches of freshly isolated neurons from the ventromedial hypothalamic nucleus (VMN) of 7-14 day old male Sprague-Dawley rats. When inside-out patches were exposed to symmetrical K⁺, the reversal potential was -2.85 ± 1.65 mV, the single channel conductance 46 pS, and the total conductance varied as a multiple of this value. Glucose (10 mM) reversibly inhibited channel activity in cell-attached preparations by 81%. In the presence of 0.1 mM ADP, 10, 5, and 1 mM ATP reversibly inhibited VMN K-ATP channels in inside-out patches by 88, 83, and 60%, respectively. This inhibition was not dependent on phosphorylation since 5 mM AMPPNP, the non-hydrolyzable analog of ATP, reversibly inhibited channel activity by 67%. Relatively high concentrations of glibenclamide (100 μM) also reversibly inhibited VMN K-ATP channel activity in cell attached and inside-out patches by 7 and 79%, respectively. Finally, the non-specific kinase inhibitor H7 (200 μM) decreased channel activity by 53% while the non-specific phosphatase inhibitor microcystin (250 mM) increased channel activity by 218%. These data suggest that while the inhibitory effect of ATP is not phosphorylation dependent, phosphorylation state is an important regulator of the VMN K-ATP channel.