sentence: Combined immunohistochemical and physiological investigations of chondrocytes have shown the expression of a number of membrane channels ,13 including aquaporin water channels14 16 as well as ENaC ,17 148 NMDA ,18 20 calcium ,21 24 chloride25 26 and sodium ion channels.27 28 The most widely reported ion channels of chondrocytes are , however , the potassium channels .