Microsoft Word - Apoptos K 110921 Asif kommentar

K efflux is observed as an early event in the apoptotic process in various cell types. Loss of intracellular K and subsequent reduction in ionic strength is suggested to release the inhibition of proapoptotic caspases. In this work, a new K-specific microelectrode was used to study possible alterations in intracellular K in Xenopus laevis oocytes during chemically induced apoptosis. The accuracy of the microelectrode to detect changes in intracellular K was verified with parallel electrophysiological measurements. In concordance with previous studies on other cell types, apoptotic stimuli reduced the intracellular K concentration in Xenopus oocytes and increased caspase-3 activity. The reduction in intracellular K was prevented by dense expression of voltagegated K (Kv) channels. Despite this, the caspase-3 activity was increased similarly in Kv-channel expressing oocytes as in oocytes not expressing Kv channels. Thus, in Xenopus oocytes caspase-3 activity is not dependent on the intracellular concentration of K. For many biological systems including the nervous system and muscle tissue, K plays an important role in setting the resting membrane potential (1). The intracellular K concentration is also important in programmed cell death (apoptosis), where altered intracellular ionic concentrations and subsequent cell shrinkage are early events (2). In Jurkat cells (3, 4) and lymphocytes (5), K efflux and a reduced intracellular K concentration release caspase inhibition, resulting in DNA degradation and eventually cell death (5). The activation of caspases is prevented by high extracellular K concentrations preventing K efflux (3). However, although K efflux is an early apoptotic event in several cell types, an alteration in intracellular ionic strength rather than the specific loss of K ions is suggested to be important (6). We have previously designed a Kselective ZnO-nanorod-covered microelectrode and reported on its stability when measuring intracellular K concentrations (7). The significant physiological role of altered intracellular K, however, makes it important also to be able to detect changes in intracellular K. The physical dimensions, biocompatibility, short response times, sensitivity, and ease of use of the microelectrode configuration make it potentially useful to study intracellular K alterations. The first aim of this work was therefore to study the possibility of using the Kselective microelectrode to detect alterations in intracellular K concentrations in Xenopus oocytes following injection of various test solutions. Measurements were done in parallel [K+]i in apoptosis