POTASSIUM CHANNEL CONDUCTANCE AS A CONTROL MECHANISM IN HAIR-FOLLICLES

The opening of intracellular potassium channels is a common mechanism of action for a set of anti-hypertensive drugs that includes the hair- growth - inducing agent minoxidil. Recent work suggests potassium chan nel openers (PCOs) also influence hair growth. Correlative studies dem onstrate that a series of PCOs including minoxidil, pinacidil, P-1075, an active pinacidil analog, RP-49,356, cromakalim, and nicorandil mai ntain hair growth in cultured vibrissa follicles. Studies using baldin g stumptail macaques verify that minoxidil, P-1075, and cromakalim but not RP-49,356 stimulate hair growth. The definition of potassium chan nels and documentation of drug effects on these channels is classicall y done using electrophysiologic techniques. Such studies require the i dentification and isolation of target cells. Both these are among the unsolved problems in the area of hair biology. Estimating K+ flux usin g Rb-86+ as a K+ tracer is an accepted method of assessing potassium c hannel conductance in other organ systems. Both pinacidil and RP-49,35 6 induce measurable Rb+ flux in isolated vibrissa follicles and a hair epithelial cell line whereas neither minoxidil nor minoxidil sulfate had measurable effects. Potassium channels have been studied successfu lly in other organ systems using specific pharmacologic blockers for t he various channel subtypes. Blockers including glyburide, tetraethyla mmonium, and procaine failed to inhibit minoxidil stimulation of cultu red follicles. The current explosion of knowledge on potassium channel biology, cloning of channels, and continued progress in hair biology promise to clarify the role of K+ ions in the control of hair follicle s.