TASK-3 dominates the background potassium conductance in rat adrenal glomerulosa cells

In a preceding study we showed that the highly negative resting membrane potential of rat adrenal glomerulosa cells is related to background potassium channel(s), which belong to the two-pore domain channel family. TWIK-related acid-sensitive K+ channel (TASK-1) expression was found in glomerulosa tissue, and the currents elicited by injection of glomerulosa mRNA (I-glom) or TASK-1 cRNA (ITASK-1) showed remarkable similarity in Xenopus laevis oocytes. However, based on the different sensitivity of these currents to acidification, we concluded that TASK-1 may be responsible for a maximum of 25% of the weakly pH-dependent glomerulosa background K+ current. Here we demonstrate that TASK-3, a close relative of TASK-1, is expressed abundantly in glomerulosa cells. Northern blot detected TASK-3 message in adrenal glomerulosa, but not in other tissues. Quantitative RT-PCR experiments indicated even higher mRNA expression of TASK-3 than TASK-1 in glomerulosa tissue. Similarly to the glomerulosa background current, the current expressed by injection of TASK-3 cRNA (ITASK-3) was less acid-sensitive than ITASK-1. Ruthenium red in the micromolar range inhibited I-glom and ITASK-3. but not ITISK-1. Like ITASK-1, ITASK-3 was inhibited by stimulation of AT1a angiotensin 11 receptor coexpressed with the potassium channel. The high level of expression and its pharmacological properties suggest that TASK-3 dominates the resting potassium conductance of glomerulosa cells.