P9.129 NOVEL AND ESTABLISHED  POTASSIUM CHANNEL OPENERS STIMULATE HAIR FOLLICLE GROWTH IN VITRO AND THEIR EFFECTS ARE OPPOSED BY INHIBITORS: IMPLICATIONS FOR THEIR MODES OF ACTION IN HAIR FOLLICLES.

Gareth C. Davies, M. Julie Thornton, Tracey J. Jenner, Y.C. Chen, John B Hansen^*, Richard D Carr^*, & Valerie A. Randall

Department of Biomedical Sciences, University of Bradford, Bradford, West Yorkshire, UK and *Novo Nordisk, Discovery Research, DK-2880 Bagsvaerd, Denmark. 

Objectives: Although ATP sensitive potassium (K_ATP) channel openers, e.g. minoxidil and diazoxide, can induce hair growth, the mechanisms involved are unclear. K_ATP channels involve the regulatory sulfonylurea receptor (SUR), with Sur1, Sur2A & 2B forms, and the inward rectifier, Kir6.1 or Kir6.2.  Which channels are involved in hair growth is unclear. While diazoxide activates both SUR1/Kir6.2 and SUR2B/Kir6.2, minoxidil has no significant effects on the SUR1/Kir6.2 channel suggesting that hair growth promoting effects operate via a SUR2 form. Therefore, the effects of established potassium channel openers and inhibitors, plus a novel, selective SUR1/Kir 6.2 opener, NNC 55-0118, were assessed on hair follicle growth in vitro. A bioassay was developed using the numerous, large follicles available from red deer (Cervus elaphus), animals bred and harvested for food.

Methods: Isolated anagen follicles from adult mature stags were cultured in serum-free William’s E medium without streptomycin, in various concentrations of potassium channel regulators. Follicle growth was measured every 24 h under the microscope.  Six follicles from each animal were incubated under each condition and at least 6 animals were used in each experiment.  Results were analysed using ANOVA.

Results: Growth was significantly increased by all concentrations of minoxidil (0.1 – 100 μM, p < 0.001) and NNC 55-0118 (1 mM p < 0.01; 0.1, 10, 100 μM p < 0.001), but only by 10 μM of diazoxide (p < 0.01). When potassium channel inhibitors were examined, tolbutamide (1 mM) significantly inhibited follicle growth (p < 0.001) alone and abolished the effect of 10 μM minoxidil, diazoxide or NNC 55-0118, while glibenclamide (10 μM) had no effect alone, but prevented stimulation by 10 μM minoxidil.

Conclusions: Therefore, deer follicles offer a useful, ethically advantageous in vitro bioassay for assessing new drugs which responds in vitro similarly to human follicles in vivo.  Since this range of potassium channel openers and inhibitors affected follicle growth in vitro, K_ATP channels appear to be involved in the direct regulation of follicle growth via at least two types of channel involving SUR 1 and SUR 2 sulphonylurea receptors.