336 Purinergic Signalling (2008) 4:331–338 Fig. 3 Double labelling of P2Y1 and P2Y2 receptors with markers for cellular proliferation, and double labelling of P2X5 receptors with markers for keratinocyte differentiation in anagen hair follicles. a Double labelling of P2Y1 receptors (red) with Ki-67, a nuclear marker for proliferating cells (green), to show that P2Y1 receptors are found in proliferating basal cells in the outer root sheath (ORS) and bulb region of the hair follicle in longitudinal section. Scale bar = 50 μm. b Transverse section: double labelling of P2Y1 receptors (red) with Ki- 67, a nuclear marker (green), to show that P2Y1 receptors are found in proliferating cells in the outer root sheath (ORS) of the hair follicle. Scale bar = 50 μm. c Longitudinal section of anagen hair follicle through the dermal papilla (DP): double labelling of P2Y2 receptors (red) with proliferating cell nuclear antigen (PCNA), a marker for proliferating cells (green), showed that P2Y2 receptors were found in the cortex (CTX) and at the edge of the medulla (M) but not in the central medulla. P2Y2 receptors were not found in the matrix (Ma), where cells were positive for PCNA. Scale bar = 75 μm. d Longitudinal section of anagen hair follicle: P2Y2 receptors were absent from the keratinised cuticle (Cu) of the hair shaft. PCNA was also found in cells of the outer root sheath (ORS). Scale bar = 75 μm. e Double labelling of P2X5 receptors (red-brown) with involucrin, a marker for differentiating cells (green). Involucrin was expressed both in the inner root sheath (IRS), cortex (CTX) and in the outermost edge of the medulla (M). P2X5 receptors were expressed in the inner (IRS) and outer root sheaths (ORS) and in the medulla (M) and matrix cells (Ma). There was yellow colocalisation with P2X5 receptors in the inner root sheath and in cells at the outermost edge of the medulla (arrow). The cortex only stained positive for involucrin, not P2X5 receptors. Scale bar=50 μm. f Transverse section: double labelling of P2X5 receptors (red) with involucrin (green). Involucrin was expressed in the inner root sheath (IRS) and cortex (CTX) and colocalised (yellow) with P2X5 receptor staining in the inner root sheath (IRS). Scale bar=50 μm