In the absence of streptomycin, minoxidil potentiates the mitogenic effects of fetal calf serum, insulin-like growth factor 1, and platelet-derived growth factor on NIH 3T3 fibroblasts in a K+ channel-dependent fashion.

There is considerable evidence to suggest that the opening of K+ channels plays an important role in stimulating mitogenesis. K+ channel blockers have been shown to inhibit mitogenesis in vitro, mitogens increase cytosolic membrane K+ channel permeability, K+ channel openers stimulate hair growth in vivo, and the Ras/Raf signal transduction pathway induces K+ channel activity. Paradoxically, however, K+ channel openers such as minoxidil have been reported in vitro not to modulate, or even to inhibit, mitogenesis in a range of cell types. Only untherapeutic concentrations have stimulated mitogenesis. These experiments, however, appear to have been carried out in the presence of aminoglycoside antibiotics, which inhibit potassium channel activity. We now report that in the absence of aminoglycoside antibiotics, minoxidil at 10 microg/ml (0.05 mM) causes a significant stimulation of proliferation of NIH 3T3 fibroblasts maintained over a 10-d period in 5% fetal calf serum-supplemented medium. Further, we show that in the presence of 100 microg streptomycin per ml, minoxidil at 10 microg/ml produces an initial inhibition of proliferation, which apparently confirms, in NIH 3T3 fibroblasts, that the inhibition of mitogenesis by minoxidil in the presence of streptomycin is an artifact. The potentiation of NIH 3T3 cell growth by minoxidil can be attributed to the opening of potassium channels, because the potassium channel blocker tolbutamide (5 mM) or combinations of the blockers tolbutamide (1 mM)/tetraethylammonium (2 mM) or glibenclamide (1 microM)/apamin (10 nM) block the minoxidil-induced stimulation of growth. We also demonstrate that minoxidil is able to significantly potentiate the mitogenic effects of both platelet-derived growth factor and insulin-like growth factor 1 on NIH 3T3 fibroblasts in the presence of CPSR-2 (a cytokine free serum substitute). Thus we have shown that minoxidil potentiates the mitogenic effects of fetal calf serum in vitro on NIH 3T3 fibroblasts by opening potassium channels and is also able to potentiate the mitogenic effects of the growth factors platelet-derived growth factor and insulin-like growth factor 1.

Modeling acne in vitro.

To help elucidate the factors responsible for the infundibular changes seen in acne, the human sebaceous pilosebaceous infundibulum was isolated by microdissection and maintained for 7 d in keratinocyte serum-free medium supplemented with 50 micrograms/ml bovine pituitary extract, 100 units/ml penicillin and streptomycin, 2.5 micrograms/ml amphotericin B and CaCl2(10H2O) to give a final Ca2+ concentration of 2 mM. Infundibular structure was maintained over 7 d in this medium; the pattern of cell division mimicked that in vivo. The rate of cell division was significantly higher than previously described for infundibula maintained in supplemented William's E medium, and moreover did not fall over 7 d. The addition of 1 ng/ml interleukin-1 alpha (IL-1 alpha) caused hypercornification of the infundibulum similar to that seen in comedones; this could be blocked by 1000 ng/ml interleukin-1 receptor antagonist (IL-1ra). In about 20% of subjects there was spontaneous hypercornification of the infundibulum that could be blocked by 1000 ng/ml IL-1ra, suggesting that the infundibulum is capable of synthesising IL-1 alpha. The addition of 5 ng/ml epidermal growth factor or 5 ng/ml transforming growth factor-alpha to the medium caused a disorganisation of the keratinocytes of the infundibulum that resulted in rupturing similar to that seen in the more severe, purulent grades of acne. The addition of 1 microM 13-cis retinoic acid caused a significant reduction in the rate of DNA synthesis and apparent parakeratosis. We are now, therefore, able to model histologically the major infundibular changes in acne.

The human hair follicle engages in glutaminolysis and aerobic glycolysis: implications for skin, splanchnic and neoplastic metabolism.

On maintenance in supplemented Williams E medium, human hair follicles grow at the normal rate, and retain their normal anagen morphology, for up to 10 days. This permits us to study their metabolism under near-physiological conditions. The ATP content of freshly isolated follicles was 124.4 +/- 10.6 pmol/follicle (mean +/- SEM; n = 50). The energy charge was 0.81 +/- 0.08 and the glycogen content 2.3 +/- 0.3 nmol/follicle. These did not alter significantly during any metabolic studies, which were performed for up to 6 h in supplemented Williams E medium. We found that the major fuel was glucose, which at physiological concentrations yields 5.47 +/- 0.77 nmol ATP/follicle/h, but 90% of the glucose was metabolised to lactate, and only 10% oxidised. Glutamine was also an important fuel, generating 2.16 +/- 0.33 nmol ATP/follicle/h, but this too was largely metabolised to lactate rather than oxidised. Lipid fuels such as palmitate or beta-hydroxybutyrate only yielded 0.72 +/- 0.15 and 0.72 +/- 0.14 nmol ATP/follicle/h, respectively, and their oxidation did not inhibit glucose utilisation. No glucose-fatty acid cycle operates in the hair follicle, therefore, but a glucose-glutamine cycle does, since the presence of glutamine will inhibit glucose utilisation.

Isolation and maintenance of the human pilosebaceous duct: 13-cis retinoic acid acts directly on the duct in vitro.

The human pilosebaceous duct was isolated and maintained for 7 days in defined medium, and defined medium supplemented with 1 microM 13-cis retinoic acid. Freshly isolated ducts retained their in vivo morphology, showing a stratified squamous keratinizing epithelium. On maintenance there was a loss of basic duct architecture, and a significant reduction in the rate of [methyl-3H] thymidine uptake. The addition of 1 microM 13-cis retinoic acid resulted in an improved duct architecture and caused a further significant reduction in the rate of [methyl-3H] thymidine uptake. [Methyl-3H] thymidine autoradiography showed that freshly isolated ducts maintained their in situ pattern of cell division. It was difficult to discern the region of cell division in ducts maintained for 7 days, but the degree of graining reflected the measured rates of [methyl-3H] thymidine uptake into PCA precipitable material. The pattern of keratin synthesis of the freshly isolated duct was similar to patterns previously described for the duct in situ. This study reports the successful isolation and maintenance of the human pilosebaceous duct, and demonstrates that 13-cis retinoic acid acts directly at the level of the duct.

An in vitro model for the study of human hair growth.

Human anagen hair follicles were isolated by microdissection from human scalp skin. Isolation of the hair follicles was achieved by cutting the follicle at the dermosubcutaneous fat interface using a scalpel blade. Intact hair follicles were then removed from the fat using watch makers' forceps. Isolated hair follicles maintained free floating in supplemented Williams E medium in individual wells of 24-well multiwell plates showed a significant increase in length over 4 days. The increase in length was seen to be attributed to the production of a keratinized hair shaft, and was not associated with the loss of hair follicle morphology. [Methyl-3H]thymidine autoradiography confirmed that in vitro the in vivo pattern of DNA synthesis was maintained; furthermore, [35S]methionine labeling of keratins showed that their patterns of synthesis did not change with maintenance. Serum was found to inhibit hair follicle growth in vitro; and when follicles were maintained in serum-free medium, they grew for up to 10 days, suggesting that in vitro the hair follicles are able to regulate their own growth, possibly by the production of relevant growth factors. This may prove useful in identifying the autocrine/paracrine mechanisms that operate in the hair follicle. The importance of this model to hair follicle biology is further demonstrated by the observations that TGF-beta 1 has a negative growth regulatory effect on hair follicles in vitro and that EGF and its other receptor ligand TGF-alpha mimic the in vivo depilatory effects of EGF that have been reported for sheep and mice.

Human hair growth in vitro.

We report for the first time the successful maintenance and growth of human hair follicles in vitro. Human anagen hair follicles were isolated by microdissection from human scalp skin. Isolation of the hair follicles was achieved by cutting the follicle at the dermo-subcutaneous fat interface using a scalpel blade. Intact hair follicles were then removed from the fat using watchmakers' forceps. Isolated hair follicles maintained free-floating in supplemented Williams E medium in individual wells of 24-well multiwell plates showed a significant increase in length over 4 days. The increase in length was seen to be attributed to the production of a keratinised hair shaft, and was not associated with the loss of hair follicle morphology. [methyl-3H]thymidine autoradiography confirmed that in vitro the in vivo pattern of DNA synthesis was maintained; furthermore, [35S]methionine labelling of keratins showed that their patterns of synthesis did not change with maintenance. The importance of this model to hair follicle biology is further demonstrated by the observations that TGF-beta 1 has a negative growth-regulatory effect on hair follicles in vitro and that EGF mimics the in vivo depilatory effects that have been reported in sheep and mice.

Organ maintenance of human sebaceous glands: in vitro effects of 13-cis retinoic acid and testosterone.

Human sebaceous glands were isolated by shearing, and maintained for 7 days either on defined medium, on medium supplemented with 3 microM-testosterone or on medium supplemented with both 3 microM-testosterone and 1 microM-13-cis retinoic acid. Freshly isolated glands retained their in vivo morphology. On maintenance, the glands retained their freshly isolated rates of cell division, but the sebocytes showed increased keratinization and there was multilayering of the peripheral undifferentiated cells. However, glands maintained in the presence of 1 microM-13-cis retinoic acid showed very little luminal keratinization and only a small degree of multilayering. On autoradiography, freshly isolated glands retained their in vivo pattern of [methyl-3H]thymidine incorporation. Similar patterns were seen when glands were maintained for 7 days with or without testosterone. However, in the presence of both testosterone and 13-cis retinoic acid there was only slight graining. Following 7 days maintenance the rate of lipogenesis fell significantly. This was partially reversed by testosterone, but further inhibited by 13-cis retinoic acid. The patterns of lipids that are synthesised after a week's maintenance are very similar to those seen in freshly isolated glands, except that the squalene:cholesterol ratio is reversibly regulated by 3 microM-testosterone and 1 microM-retinoic acid. Protein synthesis was maintained at the same rates as for freshly isolated glands under all conditions of maintenance. Whereas DNA synthetic rates were maintained in the presence of testosterone, they were significantly inhibited by 13-cis retinoic acid. Glandular wet weights were retained under all conditions of maintenance, except that they were significantly reduced by 13-cis retinoic acid. This study shows that human sebocytes continue to divide on organ maintenance, but that they do not differentiate fully. However, this provides the first demonstration that 13-cis retinoic acid acts on human sebaceous glands directly, reducing the rate of cell division and the rate of lipogenesis, which shows that the maintained human sebaceous gland might provide a useful model for studying the effect of 13-cis retinoic acid on human sebocytes.

Electrophysiological studies on isolated human eccrine sweat glands.

Human eccrine sweat glands were isolated by shearing and the potential differences across the basolateral membranes determined using bevelled micro-electrodes filled with 4 M potassium acetate. Stable resting potentials of up to -81 mV were recorded. Alterations in external potassium concentration from 1.2 to 100 mM caused the membrane potential to change over a 70 mV range in cells of high resting potential, indicating that the basolateral membrane is largely potassium permeable. Input impedance was determined by constant current injection and found to be in the range 4-80 M omega. On giving a bolus injection of acetylcholine to produce a final concentration of 10(-6)-10(-7) M, four types of response were observed: depolarization, in a proportion of cells with resting potentials of -66 to -80 mV (n = 19), hyperpolarization, in a group of cells with resting potentials of -47 to -70 mV (n = 22), no change, in some cells of -40 to -81 mV resting potential (n = 22) and micro-electrode dislodgement (n = 8). In cells depolarizing to acetylcholine, the depolarization was short-lived and in thirteen cases was followed by a 'rebound' hyperpolarization. Input impedance decreased during depolarization in one-third (n = 5) of the cells in which satisfactory measurement could be made and increased during the final phase of depolarization or during rebound hyperpolarization. In cells hyperpolarizing to acetylcholine, the hyperpolarization was usually accompanied by an increase in input impedance. In ten of the twenty-two cells which showed no change to a first dose of acetylcholine, the agonist was administered at least two more times. In two cells (resting potentials -62 mV, -64 mV) a hyperpolarization was observed whereas in three others (resting potentials -66 mV, -70 mV, -81 mV) depolarization occurred. The effects of acetylcholine, whether depolarizing or hyperpolarizing, were reversibly inhibited by atropine and irreversibly reduced by ouabain. Experiments performed on glands maintained for up to 30 h in supplemented RPMI 1640 tissue culture medium yielded essentially similar results to those performed on freshly isolated glands.