Most cells exchange ions and small metabolites via gap junction channels. These channels are made of two hemichannels (connexons). each formed by the radial arrangement of six connexin (Cx) proteins. Connexins span the bilayer four times (M1-M4) and have both amino- and carboxy-termini (NT. https://www.roneverhart.com/William-Tuttle-Hair-White-Color-Foundation-6g/