Leptin and insulin modulate the excitability of hypothalamic glucose responsive (GR) neurones by activation of K_ATP channels (Spanswick et al. 1997, 2000). Activation of K_ATP channels is potentially important in mediating the physiological effects of these hormones. Thus, we have examined the effects of a novel weight-reducing agent, BVT.12777, on GR neurone K_ATP channels.

Sprague-Dawley rats were humanely killed by cervical dislocation prior to decapitation. Whole-cell current-clamp recordings from arcuate nucleus (ARC) neurones in coronal hypothalamic slices, and single channel recordings from acutely isolated ARC neurones were made, as previously described (Spanswick et al. 1997). For cell-attached recordings, electrodes contained a high (140 mM) K⁺ solution and neurones were bathed in 135 Na⁺-containing saline. Inside-out recordings were made in symmetrical K⁺ at -40 mV. Mean channel activity was determined as N_fP_o (where N_f is the number of functional channels and P_o the open state probability) over a 120 s period. Means ± S.E.M. are given. Statistical analysis used Student’s unpaired t test.

Bath application of BVT.12777 (200 µM) caused hyperpolarisation, cessation of firing and reduced input resistance of GR neurones recorded in slices (n = 5), effects reversed on bath application of tolbutamide (200 µM, n = 3). Cell-attached recordings from acutely dispersed neurones showed that BVT.12777 (100 µM), in the recording electrode or bath applied, increased K⁺ channel activity in 58 % of patches (n = 18/31). Mean N_fP_o, 1-2 min following patch formation was 0.09 ± 0.03 and was 0.47 ± 0.12 after 5-15 min (n = 10; P < 0.01). BVT.12777-induced channel activity was inhibited by tolbutamide (200 µM) from a mean value of 0.43 ± 0.05 to 0.25 ± 0.03 (n = 4; P < 0.05). However, in contrast to leptin and insulin, BVT.12777-induced K_ATP channel activity was not reversed by the PI 3-kinase inhibitor, wortmannin (10 nM, n = 4). Inside-out patches displayed K⁺ channel activity which was inhibited by 3 mM MgATP (n = 6) and consistent with the large conductance K_ATP channels. BVT.12777 (100 µM), in the presence of MgATP, increased mean channel activity from 0.09 ± 0.03 to 0.47 ± 0.03 (n = 6; P < 0.05) in inside-out patches.

Thus, BVT.12777 activates the large conductance K_ATP channel in hypothalamic GR neurones but, unlike leptin and insulin, this action is not driven by a membrane receptor-mediated process nor mediated by PI 3-kinase.

This work was supported by Biovitrum and the Wellcome Trust.