RECEPTOR-MEDIATED REGULATION OF ISK, A VERY SLOWLY ACTIVATING, VOLTAGE-DEPENDENT K+ CHANNEL IN XENOPUS OOCYTES

Expression of IsK in Xenopus oocytes has been obtained in 2 ways: (i) by injection of cardiac polyA+ RNA from neonatal mouse heart; (ii) by injection of a cRNA synthesized in vitro. It was observed that polyA+ RNA not only directs the expression of the IsK channel but also contains purinergic P2 and endothelin receptors. Stimulation of these receptors, that produce intracellular Ca2+ increase together with diacylglycerol production activating protein kinase C, increases IsK activity. The same type of results and the same conclusions were obtained by co-injecting cRNA's corresponding to the 5-HT2 receptor and the IsK channel into oocytes. This stimulatory effect was shown to be due to Ca2+ via a calmodulin-dependent kinase process. Conversely, activation of protein kinase C pathway alone by phorbol esters leads to inhibition of IsK activity. © 1992 Academic Press, Inc.