TASK is a member of the TWIK-related (two P-domain) K+channel familyidentified in human tissues []. It is widely distributed, being particularly abundant in the pancreas and placenta, but it is also found inthe brain, heart, lung and kidney. Its amino acid identity to TWIK-1 and TREK-1 is rather low, being about 25-28%. However, it is thought to share the same topology of four TM segments, with two P-domains. TASK is very sensitive to variations in extracellular pH in the physiological range, changing from fully-open to closed in approximately 0.5 pH units around pH 7.4. Thus, it may well be a biological sensor of external pH variations.Potassium channel subfamily K member 9 (KCNK9, also known as TASK3) is a pH-dependent, voltage-insensitive, background potassium channel protein [, ].
